Your weekly research review

By Dr. Francisco Tavares
Last updated: March 15th, 2023
4 min read

Background & Objective

Day napping is a strategy frequently used by athletes to increase sleep duration and readiness to perform. Although, there seems to be little scientific evidence about the effects of naps aiding athletic performance and the effects of different napping durations on subsequent performance.

This study aimed to investigate whether or not different nap durations aided an athlete’s readiness to perform on the same day.

What They Did

Seventeen physically active men performed a shuttle test under four conditions with 72-h between each condition:
25-, 35- or 45-min nap opportunity (NAP25, NAP35, NAP45, respectively). No nap opportunity (CON).

The shuttle test consisted of six sets of 30 sec maximal shuttle sprints over 5-, 10-, 15- and 20 m with 35 sec between sets. Total distance over the 6 x 30 sec (TD), best distance (BD) and fatigue index (FI; FI (%)) were obtained. For specific information on how FI was calculated refer to the abstract link above.

What They Found

The main findings of this study were:

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Practical Takeaways

Reviewer’s Comments

“Although the participants of this study weren’t athletes, the conclusions from this study still provide us some guidance in terms of the effects of napping in performance. More precisely, this study demonstrates that napping during the day may provide benefits in terms of athletic performance.

In previous issues, I have talked about the importance of providing group (Performance Digest Issue #28) and individual education about sleep hygiene and strategies to enhance sleep time and sleep quality (Performance Digest Issue #32). Increasing total sleep duration by adding naps can be a powerful tool to be used in athletes revealing bad sleep duration and quality. These athletes can trial day napping and understand how it effects their fatigue levels and night sleep. Practitioners need to be aware that for some individual’s day napping may negatively impact on night sleep and, therefore, effect their overall sleep duration/quality.”

Want to learn more?
Then check these out…

Read this article
Listen to this podcast

The full study can be read here.

Want more research reviews like this?

Every coach understands the importance of staying up-to-date with the latest sports performance research like this, but none have the time, energy, or even enjoys spending hours upon hours searching through PubMed and other academic journals. Instead, your precious time is better-spent coaching, programming, and managing all the other more important aspects of your job.

The solution…

The Performance Digest
The Performance Digest is a monthly summary of the latest sports performance research reviewed by our team of hand-selected experts. We sift through the 1,000+ studies published in the realms of sports performance every, single month and review only those which are important to you. Each monthly issues contains 19 research reviews in all of the following disciplines:

This comprehensive topic base ensures you’re constantly expanding your knowledge and accelerating your career as quickly as humanly possible. The reviews are also hyper-focused, 1-page summaries, meaning there’s no jargon or wasted time. We cut right to the chase and tell you what you need to know so you can get back to coaching.

Join the thousands of other coaches who read it every, single month. Click here to grab your FREE copy…

[optin-monster-shortcode id=”nhpxak0baeqvjdeila6a”]

Dr. Francisco Tavares

Francisco is the Performance Coordinator for Sporting Lisbon and has previously worked as a S&C coach in elite rugby with the Chiefs Super Rugby franchise and the PRO14 team Glasgow Warriors. He holds a PhD from Waikato University and is a published author.

More content by Francisco

Do you advise your athletes and clients to take naps? If so then why, when and for how long?

The post Sleep extension through napping may effect performance appeared first on Science for Sport.

Your weekly research review

By Dr. Francisco Tavares
Last updated: March 2nd, 2023
4 min read

Background & Objective

Monitoring fatigue is important in order for practitioners to manage players training loads. However, questions about logistics and reliability are normally raised when deciding to include fatigue monitoring tests.

Therefore, it is important practitioners use tests that are easy to implement and interpret, as well as being reliable and sensitive enough to monitor fatigue. This study looked to quantify the reliability of potential measures of fatigue amongst elite youth soccer players.

What They Did

Seventeen youth soccer players competing in the English U18 Premier League participated in this study.

All players took part in regular, full training during the study (8.5 h of pitch training and 2 h of gym training per week). The group was tested twice with 7-days between testing days. The following measures were obtained:
⇒ Subjective wellness (see HERE).

⇒ Countermovement jump (CMJ), squat jump (SJ), and drop jump (DJ). For the DJ, contact time (DJ-CT), jump height (DJJH), and reactive strength index (DJ-RSI) were calculated.

⇒ PlayerLoad (PL) and individual planes of PL: anterior-posterior (PLAP), mediolateral (PLML), and vertical (PLV) were obtained from a 3, 4, or 5-min submaximal run.

What They Found

The main findings of this study were:
⇒ Subjective markers of fatigue did not meet the thresholds for acceptable reliability.

⇒ Apart from DJ-JH, all measures obtained from jump assessments met the threshold for acceptable reliability.

⇒ Apart from %PLAP, all other measures obtained from the accelerometer data obtained during the 3, 4, and 5-min submaximal run met the threshold for acceptable reliability.

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Practical Takeaways

⇒ All accelerometer variables from PL demonstrated a good test-retest reliability from 3 min of sub-maximal shuttle running, however, vertical displacements of the PL may be particularly interesting as previous research have demonstrated a relationship with a decrease in the PLV and fatigue. When using tests to monitor fatigue, practitioners need to choose not only the more reliable tests/measures, but also those that are more sensitive to monitor fatigue. This test can be a good option to monitor fatigue levels of a large group of players in a short amount of time
⇒ In addition to accelerometer variables, practitioners can also monitor heart responses during the submaximal run.

⇒ When time is not a constraint, practitioners can also rely on CMJ, SJ, DJ-RSI, and DJ-CT to monitor fatigue levels

Reviewer’s Comments

“This is an interesting study that looks at the reliability of some tests and measures that can potentially be used to monitor fatigue. Nevertheless, readers need to understand that the sensitivity of these measures to detect fatigue was not tested. Interestingly, the subjective measures did not appear to be a reliable tool to monitor fatigue, and as such, care is advised when applying these in practice, as the authors did not interpret the values based on the individual variations (see HERE).

In my experience, when accounting for the individual variations, subjective measures can be a powerful tool to help begin a dialogue between practitioners and the athlete. I have been implementing a selfmade questionnaire using questions based on sleep quality (Did you?: sleep well; sleep poorly; didn’t sleep), recovery state (1-10), soreness (What side and how much?), and pain (Where?). In addition to this, I recommend practitioners add some individual tests according to previous injuries or niggles (e.g. squeeze test, knee to wall, handgrip) in order to manage players for training.”

Want to learn more?
Then check these out…

Watch this video
Read this article
Read this article
Listen to this podcast

The full study can be read here.

Want more research reviews like this?

Every coach understands the importance of staying up-to-date with the latest sports performance research like this, but none have the time, energy, or even enjoys spending hours upon hours searching through PubMed and other academic journals. Instead, your precious time is better-spent coaching, programming, and managing all the other more important aspects of your job.

The solution…

The Performance Digest
The Performance Digest is a monthly summary of the latest sports performance research reviewed by our team of hand-selected experts. We sift through the 1,000+ studies published in the realms of sports performance every, single month and review only those which are important to you. Each monthly issues contains 19 research reviews in all of the following disciplines:

This comprehensive topic base ensures you’re constantly expanding your knowledge and accelerating your career as quickly as humanly possible. The reviews are also hyper-focused, 1-page summaries, meaning there’s no jargon or wasted time. We cut right to the chase and tell you what you need to know so you can get back to coaching.

Join the thousands of other coaches who read it every, single month. Click here to grab your FREE copy…

[optin-monster-shortcode id=”nhpxak0baeqvjdeila6a”]

Dr. Francisco Tavares

Francisco is the Performance Coordinator for Sporting Lisbon and has previously worked as a S&C coach in elite rugby with the Chiefs Super Rugby franchise and the PRO14 team Glasgow Warriors. He holds a PhD from Waikato University and is a published author.

More content by Francisco

The post Monitoring fatigue: Are subjective wellness, jumping performance, and submaximal running tests reliable? appeared first on Science for Sport.

Your weekly research review

By Dr. Francisco Tavares
Last updated: March 15th, 2023
4 min read

Background & Objective

The characterisation of physical performance in soccer matches using absolute parameters (e.g. distance covered) does not provide a comprehensive view of players load and performance.

Therefore, the authors aimed to develop and introduce a new index, known as ‘workload efficiency’, based on internal and external workload ratios. Additionally, they studied how this index was influenced by the training loads during the five days before the match.

What They Did

Fourteen players were monitored with global positioning system and heart rate sensors during forty-four on-field training sessions and sixteen competitive matches. Training loads were classified into five categories based on the number of days before game day (D-1 to D-5).

Match workload efficiency was calculated as the ratio between the equivalent distance (a measure of metabolic power; see HERE) and the modified training impulse (TRIMPmod; see HERE). External load was characterised by duration, total distance, equivalent distance, high speed (>14.4 km. h -1 ), very high speed (>19.8 km. h -1 ), sprinting (>25.2 km. h -1 ), running distances, as well as the number of medium (2.00–2.99 m. s²) and high (>3.0 m. s²) accelerations and the number of medium (-2.00– -2.99 m. s²) and high (<-3.0 m. s²) decelerations.

What They Found

The main findings of this study were:

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Practical Takeaways

Reviewer’s Comments

“This study suggested a new workload efficiency index, where the external load consisted of the equivalent distance and a modified training impulse. As the authors described, the equivalent distance “represents the distance that a player would have covered theoretically at a steady pace on grass using the total energy spent over the match or training”.

After calculating the match workload efficiency index, the authors analysed how different locomotive measures affected this index. Personally, I think that care must be taken when utilising such models, as they don’t account for possible heart rate responses to psychological factors (e.g. match-related stress, environmental factors (e.g. air temperature, humidity and height above sea level) or nutritional strategies (e.g. caffeine intake). Furthermore, the analysis used in this study provided a team average based model, neglecting important non-training related factors, such as playing position or player’s age.

As a practitioner, I always like to understand what is interesting, important, or a determinant for an athlete’s or team’s success. I believe this index is interesting, but still far off to being used in a way that will affect any athlete or team’s training schedule.”

Want to learn more?
Then check these out…

Watch this video
Read this article
Read this article
Listen to this podcast

The full study can be read here.

Want more research reviews like this?

Every coach understands the importance of staying up-to-date with the latest sports performance research like this, but none have the time, energy, or even enjoys spending hours upon hours searching through PubMed and other academic journals. Instead, your precious time is better-spent coaching, programming, and managing all the other more important aspects of your job.

The solution…

The Performance Digest
The Performance Digest is a monthly summary of the latest sports performance research reviewed by our team of hand-selected experts. We sift through the 1,000+ studies published in the realms of sports performance every, single month and review only those which are important to you. Each monthly issues contains 19 research reviews in all of the following disciplines:

This comprehensive topic base ensures you’re constantly expanding your knowledge and accelerating your career as quickly as humanly possible. The reviews are also hyper-focused, 1-page summaries, meaning there’s no jargon or wasted time. We cut right to the chase and tell you what you need to know so you can get back to coaching.

Join the thousands of other coaches who read it every, single month. Click here to grab your FREE copy…

[optin-monster-shortcode id=”nhpxak0baeqvjdeila6a”]

Dr. Francisco Tavares

Francisco is the Performance Coordinator for Sporting Lisbon and has previously worked as a S&C coach in elite rugby with the Chiefs Super Rugby franchise and the PRO14 team Glasgow Warriors. He holds a PhD from Waikato University and is a published author.

More content by Francisco

The post Workload efficiency: a new index for external and internal workload? appeared first on Science for Sport.

By Dr. Francisco Tavares
Last updated: February 18th, 2024
4 min read

Contents of Research Review

1. Background & Objective
2. What They Did
3. What They Found
4. Practical Takeaways
5. Reviewer’s Comments
6. About the Reviewer
7. Comments

Background & Objective

In many sports, a strong association has been demonstrated to exist between training load and injury occurrence, however, no study has investigated if workloads and recovery state have an influence on injuries in volleyball. As a result, in this study, the authors investigated the relationship between workloads and the athlete’s state of recovery from injuries during a 27-week elite volleyball season.

What They Did

Training loads, perceived recovery, and injury occurrence were tracked in 14 elite male volleyball players during a 27-week season period. The following measures were obtained:

• Game and training session rate of perceived exertion (RPE)
• Week workload (sum of each week session RPE)
• Weekly load monotony (average weekly workload / SD of weekly workload) Þ Weekly load strain (monotony / weekly workload)
• Weekly acute: chronic workload (A:C; Week workload / 4-week rolling workload average)
• Recovery status obtained from Total Quality Recovery (TQR; rating of recovery on a 6-10 scale [see the article link below])
• Injury occurrence was categorised according to training/game time loss: slight (no absence), minimal (1–3 days), mild (4–7 days), moderate (8–28 days), and severe (more than 28 days)

Three groups were created according to injury occurrence: 1) healthy, 2) traumatic injury, and 3) overuse injury. The analysis included the number of injuries per 1000 training/game hours which were compared to weekly workloads and A:C, differentiating pre-season and in-season periods.

What They Found

64 injuries occurred during the 27 weeks, with 53 of them being related to overuse. 46 of the injuries did not result in any time loss. The amount of injuries resulted in an occurrence rate of 14 injuries per 1000 hours of training/game.

Weekly training loads, A:C workloads, and injury occurrence during the pre-season were significantly higher than loads during the in-season. Players who had injuries (overuse and/or traumatic) had significantly higher A:C workloads and lower TQR in comparison to uninjured players. A:C workloads and TQR were found to be both a risk and a protective factor towards injury occurrence. In addition to this, the odds of athletes getting injured appear to increase by more than 3 times for players who had higher A:C workloads.

Practical Takeaways

Given that the A:C workload (read more HERE) and TQR were found to be related to injury occurrence, monitoring these variables is highly recommended to reduce the likelihood of injury.

Practitioners should pay special attention during the preseason phase when training loads and spikes in training loads are substantially increased. Although achieving “functional overreaching” is often seen as the goal of preseason periods, logical and well-structured periodisation of this phase of the season should be a focus for the coaching and medical staff. This includes not only the management of daily and weekly training loads but also the progression in training loads from week to week. The design of the training schedule should also be carefully considered to allow players to optimally recover between training sessions and match days. Furthermore, strategies such as nutrition (e.g. have snacks available for athletes to refuel between training sessions) and recovery modalities (e.g. cold water immersion) should be implemented to speed up recovery.

Reviewer’s Comments

A growing body of research has investigated the effects of training load spikes on injury occurrence. Typically, the load of a training session or a training week is compared to the mean of previous training weeks.

In this study, the weekly training load was compared to the 4-week rolling workload average, with the authors reporting that a higher A:C workload increased the odds of injury by more than 3 times. Moreover, lower TQR scores were also associated with injury occurrence. These findings reinforce 1) the need to monitor not only absolute training loads but also A:C workloads; 2) to interpret training load data in combination with recovery (objective and/or subjective) measures.

As I mentioned in the practical takeaways, pre-season training loads are typically higher in comparison to the in-season. Due to the limited duration of pre-season periods, sharp progressions in training loads are often observed which results in higher A:C workloads and an increased likelihood of injury. These findings reinforce the importance of training periodisation to gain significant adaptations and injury prevention. To avoid spikes in training loads and injuries during the pre-season, practitioners can adopt some of the following strategies with their players. These include:

• Educate the players to allocate some time to exercise during the off-season;
• Start the first week with a half-week followed by two recovery days;
• On long pre-seasons (e.g. 10 weeks), allocate one unloading week (e.g. week 4) and a taper week (e.g. week 10). On shorter pre-seasons (e.g. 4-5 weeks), allocate a week of tapering before the competitive season;
• Use individual/position-specific progressions on workloads. rather than generalising the same load volume for the entire squad.

Want to learn more?
Then check these out…

Watch this video
Read this article
Read this article
Listen to this podcast

The full study can be read here.

The post Is there a relationship between workload, the athlete’s state of recovery, and injury? appeared first on Science for Sport.

Your weekly research review

By Dr. Francisco Tavares
Last updated: March 15th, 2023
5 min read

Background & Objective

Cold water immersion (CWI) is frequently implemented by athletes to speed-up recovery. It has previously been identified that an athlete’s characteristics such as body composition influence the effects of CWI. This study compared the effects of a customized CWI (CWIc) protocol, a standard CWI (CWIs) protocol and an active recovery (AR) protocol on different measures of fatigue.

What They Did

Across three consecutive weeks, ten physical active male participants performed a fatiguing protocol (60 squat jumps and a 2 min and 30s all-out cycling time-trial). After the fatiguing protocol, the participants were exposed to the CWIc protocol (12°C, 10-17 min), CWIs protocol (15°C, 10 min), or the AR protocol (60 W, 10 min). During the CWIc, participants were exposed to a fixed temperature of 12°C with a variable immersion duration for each participant. The individual durations were calculated using the ProCcare software which is designed to predict the responses of an individual’s body temperature to CWI.

Measures of fatigue were obtained on the day prior to the fatiguing protocol, as well as 0 and 24 h after the fatiguing protocol was completed. The measures of fatigue obtained included:

What They Found

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Practical Takeaways

The findings from this study suggest that a customized CWI protocol may enhance acute recovery in comparison to a standard CWI and AR. Typically, customizing a CWI protocol is conducted by increasing exposure time, water temperature or a combination of both. This though can sometimes be challenging as due to individualised body composition characteristics such as fat mass and body weight) athletes may be exposed to varying levels of CWI intensity. By using this model, practitioners can customize CWI protocols to each athlete, therefore increasing the effectiveness of the recovery intervention.

Reviewer’s Comments

“The authors found that CWIc can have a beneficial effect on HRVr and MP in comparison to CWIs. Although, no differences were observed on the HRV post-exercise between CWI groups, suggesting that CWI may have a limited effect on HRV. Interestingly, no differences were observed for MP between CWIs or CWIc and AR. Changes in muscle temperature are associated to differences in the environmental temperature (i.e. water) and duration of exposure. As individuals using the CWIc protocol in comparison to the CWIs protocol were exposed to lower temperatures (12°C vs 15°C, respectively) and longer durations (13.0 ± 2.7 min vs 10 min, respectively), it is expected that muscle temperatures were also decreased to a greater extent. Nevertheless, if objective measures of muscle temperature were collected, it would aid to understand the observed beneficial effects of CWIc in comparison to CWIs in MP.

Although the observed effects on CWIc are a consequence of the lower temperatures and longer durations, it would be interesting if one of the CWI variables, such as temperature or duration was controlled between CWI groups. Furthermore, understanding the effects of CWIc on greater levels of fatigue (i.e. rugby match) would likely lead to a more pronounced effect of the customisation of CWI protocol.

From a personal perspective, I had the chance to try the software used to individualise the CWI protocols (ProCcare) and itis great as it offers the possibility to generate an individualise a CWI protocol by entering basic body composition measures such as body weight, height and fat mass, but also allows you to enter more complex measures such as skin area.

As mentioned in the Performance Digest issue #15, from an applied stand point, a coach or practitioner can divide the squad in two or more groups, e.g. a high and a lowfat group, and create different CWI protocols, e.g. 8 min in the CWI bin for the low-fat group and 12 min in the bin for the high-fat group. This allows for a more individualised approach to the recovery process.”

Want to learn more?
Then check these out…

Watch this video
Read this article
Read this article
Listen to this podcast

The full study can be read here.

Want more research reviews like this?

Every coach understands the importance of staying up-to-date with the latest sports performance research like this, but none have the time, energy, or even enjoys spending hours upon hours searching through PubMed and other academic journals. Instead, your precious time is better-spent coaching, programming, and managing all the other more important aspects of your job.

The solution…

The Performance Digest
The Performance Digest is a monthly summary of the latest sports performance research reviewed by our team of hand-selected experts. We sift through the 1,000+ studies published in the realms of sports performance every, single month and review only those which are important to you. Each monthly issues contains 19 research reviews in all of the following disciplines:

This comprehensive topic base ensures you’re constantly expanding your knowledge and accelerating your career as quickly as humanly possible. The reviews are also hyper-focused, 1-page summaries, meaning there’s no jargon or wasted time. We cut right to the chase and tell you what you need to know so you can get back to coaching.

Join the thousands of other coaches who read it every, single month. Click here to grab your FREE copy…

[optin-monster-shortcode id=”nhpxak0baeqvjdeila6a”]

Dr. Francisco Tavares

Francisco is the Performance Coordinator for Sporting Lisbon and has previously worked as a S&C coach in elite rugby with the Chiefs Super Rugby franchise and the PRO14 team Glasgow Warriors. He holds a PhD from Waikato University and is a published author.

More content by Francisco

The post Cold water immersion, does one-size-fit-all? appeared first on Science for Sport.

By Dr. Francisco Tavares
Last updated: June 2nd, 2024
5 min read

Contents

1. Background & Objective
2. What They Did
3. What They Found
4. Practical Takeaways
5. Reviewer’s Comments
6. About the Reviewer
7. Comments

Background & Objective

A lot of research has been conducted on different tests and methods to monitor fatigue in football. However, the practicality, reliability, and sensitivity of different methods still remains uncertain. Therefore, the objective of ‘Turning Up the Heat: An Evaluation of the Evidence for Heating to Promote Exercise Recovery, Muscle Rehabilitation and Adaptation’ by McGorm et al (2018) is to review the different methods utilised to monitor fatigue and their applicability to a real-world football environment.

What They Did

The authors reviewed a series of papers on fatigue monitoring in football and:

• Debated if monitoring fatigue after matches is needed;
• Raised critiques of the real-world relevance of the current research literature on fatigue monitoring;
• Discussed the applicability of different tests and methods, and the data they can provide to the real-world scenario;
• Proposed future research perspectives.

What They Found

In order to make it easier for the reader, I decided to present the authors’ findings point by point, using the four points presented above.

1) From a performance perspective, the authors questioned the importance of using post-match fatigue monitoring tools. Nevertheless, higher fatigue levels have been demonstrated to be related to non-contact injury, therefore, from an injury perspective, it may be useful to monitor fatigue.

2) The authors mentioned that research vulgarly interprets results independently of the players’ standard/level. Moreover, research is typically based on a single dataset. Using a single dataset may provide erroneous findings due to numerous factors such as match-to-match physiological variation, effects of training, period of the season, individual minutes of a match during the season, etc.

3) The time points used in research to analyse fatigue after matches are either too short (i.e. up to 24h post-match) or conflict with other team activities. Furthermore, research is dependent on a variety of factors that may make the data found in research non-representative of another population. The complex, expensive, and time-demanding measures used in research can rarely be implemented in everyday football environments. Although time motion measures (e.g. GPS) are collected by most teams, practitioners need to be aware of the methodological limitations. Despite being easy to apply and almost cost-free, self-reports are dependent on the players’ honesty and several other factors.

4) Suggestions were made for research to focus on the effects of neuromuscular-related fatigue on mechanical workload metrics. In order to investigate mental fatigue, mentally fatiguing tasks with high ecological validity for soccer need to be created. Researchers should also be focusing on collecting a combination of training and match-derived data

Practical Takeaways

In order to detect an individual athlete’s response to exercise, fatigue markers should be collected over a long period of time, whenever possible.

In addition, instead of collecting just a single measure of fatigue, the researchers recommend practitioners collect at least 2-3 different measures. These measures need to be appropriate to the reality of each club and training schedule. Common laboratory measures typically utilised in research (e.g. measures including nerve stimulation, electromyography, and biochemical analysis) are not practical for the real-world environment. On the other hand, practitioners must be cautious when using field tests that induce further fatigue (e.g. repeated sprints, maximal sprints, etc.).

Sub-maximal tests that can be implemented during the warm-up may be a worthwhile option. Maximal actions that do not involve extensive eccentric actions (e.g. countermovement jump) can also be a useful option. Care must be taken when selecting the measures to use, ultimately, practitioners should aim to utilise measures that are derived from training to monitor fatigue/readiness.

Lastly, practitioners should be aware of the limitations when interpreting published data and utilising methods implemented in the scientific world as they may provide little information to the real-world scenario.

Reviewer’s Comments

“My first comment is aimed at a statement made by the authors in this study. The authors suggested that even when a player is not fully recovered, they can still perform at a similar level as they can when they’re fully recovered. This comment demonstrates the limited importance of monitoring fatigue.

In my experience, self-reported tools (e.g. wellness questionnaires) still provide the most meaningful information on how a player feels. Importantly, education is a key component of these tools in order to produce valid data. From an injury prevention perspective, these self-reported tools can be combined with measures of muscular and joint health (e.g. knee-to-wall test, Lasègue’s test, etc.). Some of these tests should be implemented for the entire squad, whilst others should be individualised according to the individual’s injury history and playing position.

In order to monitor the athlete’s levels of neuromuscular fatigue, practitioners can select 1-2 tests that are commonly involved in their training programmes (e.g. 10 m sprint, CMJ, squat mean velocity, etc.). In order to have a more comprehensive indicator of fatigue, these performance results should be combined with the self-reported measures.

Fatigue monitoring measures should only be obtained when there is an actual possibility that practitioners will make changes to the programme based on the data. These changes can include a reduction in training load (e.g. decrease in the number of high-intensity meters performed, an increase in the number of reps in the tank on the gym session, etc.), a reduction in the number of sessions (e.g. 1 instead of 2 field sessions), a delay on the start of the day (e.g. if the fatigue is associated with poor/reduced sleep), or an increase in the recovery modalities and focus on recovery. It’s also worth understanding that if the athletes feel the test data is not being used for anything meaningful, they will often lose motivation to perform the test maximally, thus harming the data. So, make sure the data you collect is meaningful.”

Want to learn more?

Then check these out…

Watch this video
Read this Infographic

The full study can be read here.

Dr. Francisco Tavares

Francisco is the Performance Coordinator for Sporting Lisbon and has previously worked as a S&C coach in elite rugby with the Chiefs Super Rugby franchise and the PRO14 team Glasgow Warriors. He holds a PhD from Waikato University and is a published author.

More content by Francisco

The post Fatigue monitoring: Which metrics should we be tracking? appeared first on Science for Sport.

By Dr. Francisco Tavares
Last updated: May 31st, 2024
3 min read

Contents

1. Background & Objective
2. What They Did
3. What They Found
4. Practical Takeaways
5. Reviewer’s Comments
6. About the Reviewer
7. Comments

Background & Objective

Sleep deprivation and sleep restriction both increase fatigue and decrease readiness for training. At present, there is limited knowledge surrounding the effects of inadequate sleep on strength performance. Therefore, the aim of this systematic review is to understand the effect of sleep deprivation and sleep restriction on resistance training performance and to explore the effects of inadequate sleep on hormonal responses and markers of anabolism.

What They Did

The authors performed a systematic review which included studies based on three combined concepts: 1) inadequate sleep, 2) resistance exercise, and 3) performance and physiological outcomes.

What They Found

With regards to acute sleep deprivation (e.g. one night with no sleep), there seems to be no significant detrimental effect on muscle strength. Moreover, there also seems to be no alterations in the cortisol-testosterone profiles following acute sleep deprivation. However, studies investigating chronic sleep deprivation (i.e. 30-64 hours of no sleep) found mixed results. For example, two studies observed a reduction in strength, and one study reported no differences in strength in comparison to a control group.

Practical Takeaways

Acute sleep deprivation (e.g. one night with no sleep) appears to have no detrimental effect on strength; though there is limited research on this topic. On the other hand, extended sleep deprivation does seem to have a harmful effect on strength, with consecutive nights of reduced sleep affecting multi-joint strength.

Napping before resistance training sessions and changes in training schedule (e.g. late starts) can be effective strategies for minimising the impact of sleep deprivation on performance during periods of inadequate sleep. Lastly, group training and caffeine consumption can increase resistance training performance; however, care must be taken with caffeine intake if athletes are training late in the day (i.e. mid-afternoon onwards) as caffeine can negatively impact sleep.

Reviewer’s Comments

The authors of this study highlight a particular scenario in which athletes are likely to be subject to sleep deprivation – the birth of a new child. I can relate to this scenario as a lot of my athletes have had to deal with sleep restriction/deprivation as a result of newly-born babies. Some other scenarios that may lead to inadequate sleep include important competitions, especially for novice players, school and work-related stress, jet lag, and higher than usual training load. Practitioners must be able to identify these types of scenarios (e.g. inadequate sleep) and implement counteractive strategies such as:

• Adjust resistance-training loads
• Adjust the training schedule (e.g. late starts or
  inclusion of napping opportunities)
• Implement competition within training sessions
  (e.g. competition in some exercises)
• Pre-training nutritional strategies (e.g. caffeine
  intake)
• Training in groups

Although research is limited regarding the hormonal responses to sleep deprivation, it seems that chronic sleep restriction may lead to an inappropriate hormonal environment for adaptations to resistance training. Further research is needed to better understand the effects of inappropriate sleep on anabolic responses. Moreover, it would be interesting to explore the effects of inadequate sleep on muscle activation.

Want to learn more?

Then check these out…

Watch ‘Swans TV – Pre-season Training: Snoozeboxes‘

The full study can be read here.

Dr. Francisco Tavares

Francisco is the Performance Coordinator for Sporting Lisbon and has previously worked as a S&C coach in elite rugby with the Chiefs Super Rugby franchise and the PRO14 team Glasgow Warriors. He holds a PhD from Waikato University and is a published author.

More content by Francisco

The post How sleep impacts strength gains and what we can do about it appeared first on Science for Sport.

Contents of Research Review

1. Background & Objective
2. What They Did
3. What They Found
4. Practical Takeaways
5. Reviewer’s Comments
6. About the Reviewer
7. Comments

Background & Objective

The goal of this study was to compare the effects of cold water immersion (CWI) in football linemen (i.e. small body surface area (BSA) to body mass (BM) ratio [BSA:BM]) and cross-country athletes (i.e. large body surface area to mass ratio [BSA:BM]) performed after a heating protocol.

What They Did

The athletes were exposed to a heating protocol that consisted of 10 minutes of sitting in a heating chamber at a temperature of ~ 39 ºC and relative humidity of ~ 40 ºC followed by 20 minutes of exercise until the core temperature (Tc) reach 39.5 ºC or volitional exhaustion was achieved. After that, athletes were immersed in cold water tubs at a temperature of 10 ºC until the Tc achieved 37.5 ºC. Core temperature was measured every minute during the cold water immersion (CWI) and was obtained from a temperature sensor that was ingested by the athletes. The analysis was performed once the athletes’ had reached a Tc of 37.5 ºC, which in this case, was after 7 minutes. Therefore, the first athlete was removed from the CWI tub after 7 minutes (e.g. achieved Tc of 37.5 ºC after 7 minutes).

What They Found

Differences between the groups were found for the cooling time to achieve the Tc of 37.5 ºC (target Tc / time) and slope of lines of the Tc / time. The football linemen (FB) required significantly more time to reduce Tc to 37.5 ºC (~ 11 minutes) than the cross-country (CC) athletes (~ 8 minutes). As expected, the Tc / time was significantly lower in the FB (~ 0.156 ºC per minute) in comparison to CC (~ 0.255 ºC per minute). Strong correlations were found between the rate of cooling and body mass, total BSA, BSA/mass, lean body mass/mass and % of body fat.

Practical Takeaways

The main takeaway message from this study is that body composition affects the decrease in Tc when athletes are exposed to CWI. In particular higher measures of body mass, total BSA, BSA/ mass, lean body mass/ mass and % of body fat are associated with a decrease in the rate of cooling of Tc.

Another important finding from this study is that cooling rates vary considerably between subjects, reinforcing the need to monitor individual rectal temperature during CWI. Lastly, a CWI protocol of 11 minutes at a temperature of 10ºC seems to be ideal for large athletes such as football linemen or other athletes such as rugby first rows.

Reviewer’s Comments

The findings from this study demonstrate that decreases in Tc from CWI are highly correlated with different measures of body composition. Subjects with lower BSA:BM should be exposed to more severe cold protocols in comparison to smaller BSA:BM when reductions in the Tc are desirable.

While it can be difficult to have cold baths with different temperatures within the same environment, by increasing the duration of the protocol one can increase the intensity of the modality when individualisation is desirable. Given that strong correlations were observed between the rate of cooling and % of body fat, coaching staff can use % of body fat as a reference to individualise CWI interventions.

Although I have never used the BSA:BM to individualise CWI interventions, I have provided some individualisation based on two factors: 1) perceived effectiveness and belief in CWI as a recovery modality; and 2) the percentage of fat mass. In order to respond to these two factors, I use cold tubs at different intensities, categorising them as severe (~ 10 ºC) or less severe (~ 15 ºC) and using different immersion times (e.g. 8 or 10 minutes). With this, I can have a combination of 4 different intensities:

Low: 8 minutes at 15 ºC;
Moderate – Low: 10 minutes at 15 ºC;
Moderate – High: 8 minutes at 10 ºC
High: 10 minutes at 10 ºC

Want to learn more?
Then check these out…

Read ‘Cold-Water Immersion for Athletic Recovery: One Size Does Not Fit All‘.
Read ‘Influence of body composition on physiological responses to post-exercise hydrotherapy‘.

The full study can be read here.

Dr. Francisco Tavares

Francisco is the Performance Coordinator for Sporting Lisbon and has previously worked as a S&C coach in elite rugby with the Chiefs Super Rugby franchise and the PRO14 team Glasgow Warriors. He holds a PhD from Waikato University and is a published author.

More content by Francisco

The post Should we be individualising ice baths? The influence of body size and immersion time appeared first on Science for Sport.

1. Objective
2. What the researchers did
3. What the researchers found
4. Practical Takeaways
5. Author’s comments
6. References
7. About the author

Objective

Team ball sports, such as football and rugby, are extremely demanding and can, therefore, lead to a remarkable level of fatigue. While different sports have been investigated, no previous research has systematically reviewed the differences in sports and markers of fatigue. Therefore, the goal of this study was to investigate post-match recovery of different performance and biochemical markers typically used to monitor fatigue/ readiness in team ball sports.

What the researchers did

Twenty-eight studies were included for analysis. The most common performance measures used were the countermovement jump (CMJ) and sprint tests, while creatine kinase (CK), cortisol (C), and testosterone (T) were the most frequently used biochemical markers, respectively.

What the researchers found

The CMJ was mostly affected for up to 12 and 24 hours after a match. In comparison to other sports, basketball appears to affect CMJ performance for a longer period of time. Sprint performance is mostly affected on the first measure after a match and also affected to a greater extent after a soccer match in comparison to other ball team sports.

Although in most cases these performance markers (i.e. CMJ and sprint performance) seem to return to baseline within 48 hours, longer periods were observed for CMJ (i.e. 72 hours) and sprint performance (i.e. 96 hours) after a match. Importantly, the time needed for these performance measures to return to baseline seems to be dependent on the competition level of the athlete, with lower competition level athletes demonstrating longer recovery periods in comparison to higher competition levels (e.g. amateur vs professional).

In some of the studies covered in this systematic review, CK did not return to baseline within the times of measurement, while in other studies, CK returned to baseline 42, 48, 72 or 120 hours after a match. Peak CK after exercise and time-to-return to baseline appears to be greater in football and rugby in comparison to other team ball sports. This is likely to due to the greater number of high-intensity efforts performed during a match, such as accelerations/decelerations, sprints, collisions, and total running volume.

Cortisol seems to peak immediately after a match and return to baseline in different time periods (i.e. 14-72 hours). For the same reasons as CK, the recovery times of cortisol are also longer in rugby and football. Different findings can be found in testosterone changes after a match. There seems to be a trend for testosterone to decrease after a match and then increase in the longer periods of recovery (i.e. 24-48 hours post-match).

Practical Takeaways

The results from this study demonstrate that it takes approximately 48 hours after a match for an athlete to recover from a performance standpoint and up to 72 hours for certain biochemical markers to recover (e.g. CK). These findings are important because they demonstrate that although athletes can regain performance (e.g. CMJ and sprint speed) 48 hours after a match, it does not mean that athletes are fully recovered from a muscle damage standpoint, for example.

Therefore, at certain periods within the season, athletes should be allowed to fully recover, or at the very least, strategies should be implemented to speed up recovery in order to avoid accumulative fatigue. In addition, when working with sports where athletes are exposed to higher volumes during matches, such as rugby (i.e. 80 minutes) and football (i.e. 90 minutes), practitioners must be fully aware that the time needed to recover is longer, including how long it takes to fully recover.

Author’s Comments

“This study aimed to investigate the recovery time of different markers of fatigue in different team-sports. However, it is important to mention that from the 28 studies used for analysis, only five did not refer to football and rugby. Further research investigating the effects in other team ball sports are therefore warranted.

When working with team-sport athletes, after a match, I normally allow 36-48 hours for recovery and start the training week with a low-volume and low-intensity field session (see my second study review in this issue of the Performance Digest for an example). Supporting the findings that athletes can still perform close to their maximum without being fully recovered (e.g. increased biochemical markers), I believe that athletes should have a full recovery time-period frequently (e.g. 48-72 hours every 4-6 weeks).

However, these decisions will be highly dependent on the competition schedule. Some good options can be to rest an athlete for a game (e.g. full weekend off), a training week, or part of the training week (e.g. weekend and beginning of the week). These practices are very common in professional sports and can be applied across the board to various levels of competition.

Lastly, it is important to understand that fluctuations in training loads are needed to ensure periods where athletes are given the opportunity to recover and adapt. During these periods, when the total training load (i.e. combination of field, gym, meetings, etc.) is lower than what the athletes are used to, practitioners can expect a reduction in accumulative fatigue (e.g. biochemical markers) and therefore an increase in recovery and ‘freshness’.”

The post How long does it take to fully recover after a competitive match? appeared first on Science for Sport.

By Dr. Francisco Tavares
Last updated: April 3rd, 2024
1 min read

You can view the original study and source of the information here.

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1. Summary
2. What is the Dynamic Strength Index?
3. Why is the Dynamic Strength Index important?
4. How do you calculate the Dynamic Strength Index?
5. Is the Dynamic Strength Index valid and reliable?
6. How should the Dynamic Strength Index guide your training program?
7. References
8. About the Author

Summary

The Dynamic Strength Index, often referred to as the dynamic strength deficit, measures the difference between an athlete’s maximal and explosive strength capacity. However, the term “index” is preferred over “deficit”, as it’s an index of the athlete’s current performance ability. The dynamic strength index can be used to identify whether the athlete may require maximal strength training, ballistic strength training, or concurrent training (i.e. a combination) as a stimulus in their programme. It can also be used to reliably measure the performance capabilities in both the lower- and upper body and in recreational, university, and elite athletes.

What is the Dynamic Strength Index?

The Dynamic Strength Index (DSI), otherwise known as the Dynamic Strength Deficit (1) or the Explosive Strength Deficit (2-4), is simply a ratio between an athlete’s ballistic peak force and their dynamic or isometric peak force (5). In another sense, it may be viewed as a “strength potential” test.

An example of ballistic peak force would be an athlete’s maximal force production during a countermovement jump (CMJ) – as this is a ballistic movement. On the other hand, dynamic peak force may be measured using a 1 repetition maximum (1RM) back squat, whilst an isometric mid-thigh pull (IMTP) may be used to measure their peak force production during an isometric test. It is very common for practitioners to use a CMJ or squat jump (ballistic tests) and an IMTP (isometric test) to calculate an athlete’s DSI (3, 5, 6). Put simply, the DSI measures the difference between an athlete’s ability to produce force during a dynamic or isometric test, versus their ability to produce force during a ballistic exercise. This allows the strength and conditioning coach to identify the athlete’s “strength potential” and how much of that potential they can use during a high-speed ballistic movement.

Calculating the DSI allows the strength and conditioning coach to do two things:

1. Determine the maximal amount of force an athlete can produce (e.g. using the IMTP test).
2. How much of that total force can they produce in a high-speed movement with a short time frame – i.e. 400 milliseconds (ms) is the time it takes to achieve peak force during the CMJ (7).

Just to clarify, the IMTP or 1RM dynamic back squat is used to measure an athlete’s maximal force capabilities (i.e. maximal strength), whilst the CMJ, which is a ballistic movement, is used to determine how much of their total force capability can they produce in a very short timeframe.

Why is the Dynamic Strength Index important?

The DSI provides the strength and conditioning coach with valuable information regarding how forceful (i.e. strong) the athlete is, and how much of that strength they can use during fast movements. This information allows the coach to design a more specific training programme focussed on developing an athlete’s strength and/or power capacities (6).

The Importance of Maximal Strength
High muscular strength is considered a vital element of athletic performance. Greater muscular strength has been shown to enhance the ability to perform general sports skills such as jumping, sprinting, and change of direction tasks, improve overall performance, allow athletes to potentiate earlier and to a greater extent, and even reduce the risk of injury (8).

To add to this, maximal strength is strongly related to power output (r = 0.77-0.94 [9]) for both the lower- (10-13) and upper body (10, 14-17). Therefore, an athlete’s ability to produce power is largely dependent on their maximal force capacity (i.e. strength) (18-20). As a result, the “first box to be checked” so to speak when performing a strength diagnosis, is perhaps an athlete’s maximal strength.

The importance of being able to produce high force in a short time frame, Kawamori et al. (2006) (7) observed that it took approximately 260 ms to achieve peak force during the IMTP and 400 ms during the CMJ. Other research has shown time to peak force during the CMJ to take approximately 240 ms (21). So whilst the time to achieve peak force during the IMTP (260 ms) can be somewhat similar to the CMJ (240-400 ms), it is in fact how ‘much’ force is developed that separates the two exercises.

Table 1 provides a clear example of how the peak force differs between the IMTP and the CMJ. Thus, the important factor is to determine how much force an athlete can produce under no time constraints (e.g. IMTP) versus how much force they can produce under short time constraints (e.g. CMJ).

Below are some examples of common ground contact times during particular sporting movements:

• Basketball lay-up shot = 218 ms (22)
• Sprinting = 80-90 ms (23)
• Long Jump = 140-170 ms (24)

As many sporting movements, such as those above, happen in a very short time frame and are all ballistic in nature, it is vital to analyse the athlete’s ballistic force production capabilities under short time constraints.

How do you calculate the Dynamic Strength Index?

The equation below is used to calculate an athlete’s DSI. And although it is referred to as a “ratio”, it is not displayed as a one and is instead a simple division between ballistic and dynamic or isometric peak forces.

Dynamic Strength Index (DSI) = Ballistic Peak Force / Dynamic or Isometric Peak Force
Example:
Using the data from Table 1.

Dynamic Strength Index (DSI) = CMJ peak force (N) / IMTP peak force (N)
DSI = 1450 / 3178
DSI = 0.46

Is the Dynamic Strength Index valid and reliable?

The DSI has been proven to be both a valid and reliable measure of maximal and explosive strength capacity in recreational (6), university (5), and elite athletes (25). Furthermore, the following combination of exercises have been proven to be reliable when measuring DSI:

• CMJ and IMTP (3)
• Static SJ and IMTP (5, 6)
• Ballistic Bench Throw and Isometric Bench Press (26)

It has also been verified as a sensitive and useful tool to evaluate and monitor performance changes over the course of a training programme (26).

How should the Dynamic Strength Index guide your training program?

Once the athlete’s DSI has been calculated, the strength and conditioning coach needs to know what that score tells them, and therefore how to design the training programme based on that score. Table 2 provides some simple examples of various DSI scores.

The DSI reflects the percentage of maximal strength “potential” which is not being used within a given motor task (e.g. jump) (27). In other words, it demonstrates the athlete’s ability to use their full “force potential” during a ballistic exercise such as a CMJ. So theoretically speaking, if an athlete can express a DSI score of 1 (i.e. Athlete C in Table 2), they are capable of using their full “force potential’. This means the higher the athlete’s DSI, the more capable they are at utilising their “force potential” during a ballistic exercise.

In contrast, the lower the athlete’s DSI, the less capable they are at utilising their “force potential” during a ballistic exercise. A higher DSI means more time should be spent on developing maximal strength (i.e. force production). A smaller DSI means more time should be spent developing RFD using ballistic strength training methods (Table 3) (6).

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