RESEARCH: Studies from 12 to 18 May 25
Sharing research and insights from coaches, scientists and athletes to help us improve endurance performance.
This week’s quick summary:
Muscle reoxygenation after higher intensity and in different muscle sites
Low-glycemic load diets and thyroid function
Training intensity distribution of a 7-day HIIT shock microcycle
Sports diet and oral health in athletes
Whole-body cryotherapy and post-match recovery
PHYSIOLOGY: Muscle reoxygenation is slower after higher cycling intensity, and is faster and more reliable in locomotor than in accessory muscle sites
Near-infrared spectroscopy (NIRS) provides a non-invasive method to monitor muscle oxygenation during dynamic exercise. Prior studies have established that reoxygenation kinetics post-exercise can reflect muscle recovery and cardiovascular function. In this study, the authors sought to “determine how exercise intensity and muscle location influence post-exercise reoxygenation and its measurement reliability”.
STUDY DETAILS
21 trained cyclists completed two incremental cycling trials with 5-min work stages and 1-min rests.
NIRS measured reoxygenation in four muscles: vastus lateralis (VL), rectus femoris (RF), lumbar paraspinal (PS), and lateral deltoid (DL).
Reoxygenation was assessed using half-recovery time (HRT) after each workload (50%, 75%, and 100% peak power).
HRT increased (slower reoxygenation) with higher workloads in VL, RF, and PS, but not in DL.
VL showed the fastest and most reliable reoxygenation across intensities; DL was slowest and least reliable.
PRACTICAL TAKEAWAY
This study showed that NIRS reoxygenation metrics are most reliable when measured in the vastus lateralis during cycling and that locomotor muscles provide more consistent data than accessory sites. I find NIRS to be an interesting, yet complex means of assessing physiology in athletes. This study shows that knowledge of where to place the sensors is important. My recommendation for coaches or athletes intending to use NIRS is to find a sports scientist with good knowledge of the specifics of measurement and who understands how to interpret the data effectively. I’ve learnt a lot from Jem Arnold so if you want to explore this topic in more detail then I recommend following him.
RELATED RESEARCH
NUTRITION: Low-glycemic load diets and thyroid function
Previous research suggests that nutrition and calorie intake can subtly influence thyroid function. Factors like iodine deficiency and extreme caloric shifts, such as those seen during starvation or overfeeding, may disrupt thyroid hormone levels. Additionally, macronutrient and micronutrient composition appears to modulate thyroid function. Low-glycaemic load (LGL) diets have recently gained popularity for their effectiveness in managing various conditions, including diabetes, obesity, and cardiovascular disease. In this review, the authors set out to "assess the relationship between low-glycemic load diets and thyroid function in healthy individuals and those with thyroid disorders".
REVIEW DETAILS
Participants across studies included both healthy individuals and patients with thyroid-related conditions, though demographic details and sample sizes varied widely.
The intervention involved LGL diets characterised by reduced carbohydrate intake and lower postprandial glucose and insulin responses.
The duration of interventions ranged from a few weeks to several months, depending on the individual study design.
Thyroid function was assessed using serum measurements of TSH, free T3, and free T4, alongside clinical assessments of thyroid status.
Results were inconsistent across studies—some reported improved thyroid hormone profiles with LGL diets, while others showed no significant changes or mixed effects.
PRACTICAL TAKEAWAY
This review showed that while LGL diets have known metabolic benefits, their effect on thyroid function is inconclusive. My recommendation for athletes who are concerned that they may have low thyroid levels (the symptoms can be fatigue, changes in resting heart rate, and mood changes), is to seek out professional help. Firstly, the diagnosis itself is challenging, and secondly, an intervention like the low-glycaemic diet in this review is not effective. A good diagnosis and proper intervention are required.
RELATED RESEARCH
TRAINING: Training intensity distribution of a 7-day HIIT shock microcycle: Is time in the "red zone" crucial for maximising endurance performance?
Research has established that different intensity measures influence training intensity distribution assessments. Existing studies using mesocycles and macrocycles have not addressed HIIT shock microcycles. In this study, the authors sought to “compare various intensity measures during a 7-day HIIT shock microcycle to evaluate endurance performance changes".
STUDY DETAILS
29 endurance-trained individuals were allocated into three groups.
Participants underwent a HIIT shock microcycle of ten high-intensity interval sessions.
One group performed additional low-intensity training while others did not.
Measurements included training intensity distribution via running velocity, power, heart rate, and oxygen uptake.
Results revealed polarised patterns for running metrics and a pyramidal pattern for heart rate, with running velocity most closely linked to performance improvements.
PRACTICAL TAKEAWAY
This study showed that relying solely on heart rate may underestimate true intensity during HIIT sessions. I think most coaches and athletes already know that heart rate is not a good indicator for prescribing and analysing the intensity of short intervals. This study showed that running speed was the most effective metric to help measure intensity during these types of sessions. My recommendation for athletes completing intervals shorter than 3 minutes, is to use running speed or RPE as the metric for intensity.
RELATED RESEARCH
GENERAL: Sports diet and oral health in athletes
Athletes often rely on high-carbohydrate and frequent nutrient intake to support performance, but this can contribute to oral health problems such as dental caries and periodontal disease. Previous research has shown a high prevalence of such conditions among elite athletes, with dietary patterns, oxidative stress, and oral hygiene practices being key contributing factors. In this review, the authors aimed to “clarify nutritional influences on oral health”.
REVIEW DETAILS
The review focused on elite athletes, citing studies showing caries in 20–84%, erosion in 42–59%, gingivitis in 58–77%, and periodontal disease in 15–41%.
Frequent intake of sugars and carbohydrates during training and competition was identified as a major contributor to oral diseases.
Polyunsaturated fats and insufficient protein intake were also discussed as dietary risk factors affecting oral health.
Oxidative stress from high training loads may increase vulnerability to oral inflammation and periodontal conditions.
The review emphasised the need for nutrition strategies aligned with oral hygiene to support both performance and dental health.
PRACTICAL TAKEAWAY
This review showed that frequent carbohydrate intake, particularly sugars, common in sports diets can significantly raise the risk of dental caries and periodontal disease in athletes. My recommendation for athletes is to always have water with them to rinse their mouth after ingesting sports drinks, gels, or bars. It also may be worth brushing teeth after sessions where high volumes of sugar have been ingested.
RECOVERY: Chill without thrill - a crossover study on whole-body cryotherapy and postmatch recovery in high-level youth basketball players
Whole-body cryotherapy (WBC) is widely used in sport to accelerate post-exercise recovery. Prior research has focused on adult athletes and has shown mixed results, particularly for objective markers of performance and recovery. In this study, the authors aimed to “assess the effect of whole-body cryotherapy (WBC) on postmatch recovery in youth basketball players”.
STUDY DETAILS
17 high-level male youth basketball players (age 16.2y) completed two simulated matches in a randomised crossover design.
After each match, players underwent either WBC (4min at −75 to −85°C) or a placebo control recovery.
Performance (jump, sprint, agility), heart rate variability, perceived recovery, and muscle soreness were assessed at four time points: prematch, postmatch, postrecovery, and 24h postmatch.
WBC led to higher perceived recovery scores than control immediately after treatment, but this may have been influenced by baseline differences.
No differences were observed between interventions in objective performance metrics or recovery markers at any time point.
PRACTICAL TAKEAWAY
This study showed that whole-body cryotherapy had minimal impact on objective recovery measures in youth basketball players. While it slightly improved subjective perceptions of recovery, these effects may not reflect real physiological benefits. My recommendation is to stay away from cold-water immersion, cryotherapy, or any other cold-based recovery strategies. There is now plenty of evidence to show that these strategies are most likely detrimental rather than beneficial.
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Quick summary from last week’s paid newsletter
Paid subscribers receive a newsletter every week and have full access to all newsletters listed in the archives (635 studies and practical takeaways). Last week, the newsletter covered studies on the following topics:
Dynamic stretching during warm-up improves running economy
Residual effects of same day lower extremity strength training
Morning versus nocturnal heart rate and heart rate variability
Carbohydrate and energy expenditure during endurance exercise
The effect of water dousing on heat strain and performance
