RESEARCH: studies reviewed this month - April 2020

DETRAINING: Two Weeks of Reduced Activity Decreases Leg Lean Mass and Induces "Anabolic Resistance" of Myofibrillar Protein Synthesis in Healthy Elderly

During the period of quarantine in 2020 I was investigating the rate of detraining and the impact of reduced training load. This study looked at age-related muscle atrophy with the hypothesis that "during periods of muscle disuse, muscle protein synthesis is blunted, and muscle atrophy occurs in young and old". In particular the authors investigated "the impact of a short reduction in physical activity on muscle protein metabolism in older adults".

The methodology involved a 14-day period of reduced daily steps hoping to determine the impact on either a fasted and fed-state rate of myofibrillar protein synthesis (MPS). The results showed that:

Leg fat-free mass was reduced by approximately 3.9%. Postabsorptive insulin resistance was increased by approximately 12%, and postprandial insulin sensitivity was reduced by approximately 43% after step reduction. Postprandial rates of MPS were reduced by approximately 26% after the intervention, with no difference in postabsorptive rates.

14 days of reduced steps in older adults induces small but measurable reductions in muscle mass that appear to be underpinned by reductions in postprandial MPS and are accompanied by impairments in insulin sensitivity and systemic inflammatory markers and postprandial MPS.

PRACTICAL TAKE AWAY - as little as 14 days of reduced activity has an impact on older adults. Therefore it would be valuable to include some exercise and training even in a post-season break rather than having a period of complete rest.

NUTRITION: Effects of caffeine on neuromuscular function in a non‐fatigued state and during fatiguing exercise

This study aimed to identify the mechanisms of caffeine with a particular emphasis on the neuromuscular function. Subjects in the caffeine group took a 6 mg·kg−1 dose of caffeine one hour before testing. This is on the higher end of caffeine doses as typical sports specific doses are recommended in the 3-6mg·kg-1 doses. The authors found that there were significant benefits to taking caffeine:

Caffeine enhanced drop jump height and decreased the transcranial magnetic stimulation (SP) in a non‐fatigued state.

A caffeine‐related decrease in SP and short‐interval intracortical inhibition before the fatiguing activity was associated with an increased time to task failure.

The participants who benefitted from an improved performance on the caffeine day reported a significantly lower sense of effort during exercise and had an accelerated postexercise recovery of M‐wave amplitude.

Caffeine modulates inhibitory mechanisms of the CNS, recovery of M‐wave amplitude and perception of effort.

PRACTICAL TAKE AWAY - caffeine can improve performance through neuromuscular functions in both non-fatigued and fatigued states. The recommended dose is 6mg·kg-1 taken one hour before exercise.

HEAT: Wearing a Cap, Thermoregulation, and Thermal Sensation During Running in a Hot Environment

This study is useful for anyone who has wondered whether using a cap is beneficial for heat or if the added sensation of heat on the forehead is actually detrimental. The study tested runners in a 31C condition during a one hour run. The results showed that:

There were no significant differences in rectal temperature, skin temperature or whole-body sweat loss between conditions in CAP of NOCAP conditions.

There were no differences in heart rate or rating of perceived exertion between conditions.

PRACTICAL TAKE AWAY - while it seems that there are no negative consequences from a thermoregulation perspective to wearing a cap, there aren't necessarily any benefits. Therefore choosing to wear a cap is a personal choice and should be based on what feels best to the athlete.

HEAT: Cooling the Neck Region During Exercise in the Heat

Using a scarf or bandana of ice around the neck is a common strategy during hot events. This study set out to find out if cooling the neck could improve the ability to exercise in hot environments. The participants either used a placebo or cooling neck collar (CC) during exercise in an environmental chamber. The results showed that:

Time to volitional exhaustion was increased by 13.5%. Participants terminated exercise at identical levels of perceived exertion, thermal sensation, and feeling scale, but the CC enabled participants to tolerate higher rectal temperatures and heart rates at the point of termination.

PRACTICAL TAKE AWAY - cooling the neck may improve performance in the heat through lowering the perceived levels of thermal strain.

TRAINING: Physiological profile of adult male long-distance trail runners

What are the key features that distinguish the level of competitiveness of trail runners? This study set out to "describe and identify the importance of different indicators of the aerobic and anaerobic fitness of male ultra-trail runners according to their level of participation (regional or national)". Th key differences between athletes at the different levels were:

Differences were uniquely significant for the second ventilatory threshold.

When aerobic fitness was expressed per unit of body mass, differences were significant for the second ventilatory threshold and also maximum volume of oxygen.

PRACTICAL TAKE AWAY - as the second ventilatory threshold was the significant indicator of level, it would seem that training to develop this capacity would be critical to improve performance.

SLEEP: Influence of a 30-Day Slow-Paced Breathing Intervention Compared to Social Media Use on Subjective Sleep Quality and Cardiac Vagal Activity

This study is particularly relevant now with wide-spread mobile phone and tablet use by all athletes. The study set out "to investigate the influence of a 30-day slow-paced breathing intervention compared to social media use on subjective sleep quality and cardiac vagal activity". The slow-breathing group did 15' of a breathing exercise in place of using social media before sleeping. The results showed that:

In comparison to the use of social media, the slow-paced breathing technique improved subjective sleep quality and increased overnight CVA.

PRACTICAL TAKE AWAY - at the least, stop using social media before bed. If possible, substitute it for slow-breathing (or biofeedback).

TRAINING: Multidisciplinary Analysis of Differences Between Finisher and Non-finisher Ultra-Endurance Mountain Athletes

I have shared a couple of studies which predict the level of performance of ultramarathon athletes: this study showed that maximal aerobic speed and leg strength are important, while this study found that preparing for the specific demands of the race are vital. In this study the authors set out out:

  • to analyze differences in selected psychophysiological parameters between finisher and non-finisher ultra-endurance mountain athletes;
  • to analyze modifications in psychophysiological parameters before and after an ultra-endurance mountain event.

The authors found that:

  1. An ultra-endurance mountain race produced dehydration, a decrease in systolic blood pressure, weight and leg strength muscle values, as well as an increase in heart rate and rate of perceived exertion values.
  2. Finishers presented lower systolic blood pressure, weight, body mass index, half marathon time and fluid intake before competition day compared to non-finishers.
  3. Body mass index, pre-race hydration, and performance in lower distance races were predictors of performance in these ultra-endurance mountain races.

PRACTICAL TAKE AWAY - general fitness (lower weight, experience in shorter races) were significant indicators of ultramarathon performance. In addition, hydration status both before and after the event was a differentiator indicating the importance of hydration during these events.

NUTRITION: Effects of an Exogenous Ketone Supplement on Five-Kilometer Running Performance

Previously I shared a study showing that ketone ingestion impaired time trial performance. This study set out to determine if ketone ingestion (oral β-hydroxybutyrate-salt + Medium Chain Triglyceride) would induce ketosis and whether this would improve a 5km running time trial performance. The results showed that:

Plasma R-βHB (endogenous isomer) was elevated from baseline and throughout the entire protocol under the βHB-salt+MCT condition.

No significant difference was observed between the βHB-salt+MCT supplement and the placebo in time to complete the 5KTT.

PRACTICAL TAKE AWAY - ketone supplementation does not improve 5km running performance.

HEAT: Humid heat acclimation does not elicit a preferential sweat redistribution toward the limbs

This study set out to better understand how the body acclimates to heat in a hot environment. The authors found that:

Our data render untenable the hypothesis that heat adaptation is universally accompanied by a trunk-to-limb sweat redistribution.

Our observations are consistent with the hypothesis that postacclimation changes in the sweat threshold may be more sensitive to the absolute change in body temperature encountered during a heat exposure, particularly that of the core, rather than to the attainment of some predetermined body temperature.

PRACTICAL TAKE AWAY - the details of the study suggest that after just 8 days there was an acclimation to heat and at 22 days the rate of acclimation was even greater but not as significant a jump as the first period. A heat adaptation protocol of 8 days is a good starting point for preparing for hot races.

HEAT: Heat alleviation strategies for athletic performance: A review and practitioner guidelines

"This review provides a focused perspective of the relevant literature describing how practitioners can structure male and female athlete preparations for performance in hot, humid conditions". There is a large amount of detailed information on bith chronic and acute interventions included in this review. It is detailed and extensive and worth reading further to understand more than just these summary points:

  • HA provides a robust opportunity to improve thermoregulatory and performance physiology, alongside thermal perception, for athletes who are likely to be impacted by the predicted climate.
  • Athletes may utilize a singular or combined method HA strategy that includes exercise-heat stress and/or post-exercise heat stress e.g. hot water/sauna, to fit individual needs and circumstances.
  • Once- or twice-daily HA sessions of 30–90 min may be used to optimize the magnitudes of adaptation in a manner that compliments training.
  • Athletes should “prepare for the worst” by preparing to perform in environments equal too or greater than maximum anticipated climatic conditions including radiative (solar) heat.
  • Structured HA may be performed weeks prior to the competition, with subsequent “top-up” sessions implemented closer to individual events.
  • Athletes should rehydrate post HA and will benefit from carbohydrate and protein consumption to aid recovery and adaptation.
  • Acute heat alleviation such as pre- and mid-event cooling should compliment chronic HA strategies.
  • Acute strategies should be individualized, and well rehearsed prior to competition to optimize responses.

PRACTICAL TAKE AWAY - preparing for a hot and humid event is possible, but it will take time and resources to do effectively.

TRAINING: Physiological adaptations to interval training and the role of exercise intensity

"This brief review considers the role of exercise intensity in mediating physiological adaptations to training, with a focus on the capacity for aerobic energy metabolism". The review compares high-intensity interval training (HIIT), sprint-intensity training (SIT) and moderate-intensity continuous training (MICT). The authors showed that:

It is well established that SIT increases mitochondrial content to a similar extent to MICT despite a reduced exercise volume.

At the whole‐body level, VO2Max is generally increased more by HIIT than MICT for a given training volume, whereas SIT and MICT similarly improve VO2Max despite differences in training volume.

There is less evidence available regarding the role of exercise intensity in mediating changes in skeletal muscle capillary density, maximum stroke volume and cardiac output, and blood volume.

In summary, interval training is a powerful stimulus to elicit improvements in mitochondrial content, however, we know relatively little regarding the influences of exercise intensity, duration, and frequency on other components of the integrative physiological response to interval training.

PRACTICAL TAKE AWAY - while interval training is clearly beneficial, there remains work to understand how best to structure training sessions for maximal benefit.

DETRAINING: One Week of Step Reduction Lowers Myofibrillar Protein Synthesis Rates in Young Men

Similar to the first study on this page, this study set out to determine "the impact of reduced physical activity and increased sedentary time on daily myofibrillar protein synthesis rates in healthy young men". The study reduced the activity of the participants by 91% in the second week (after a monitored control week) finding that:

Daily myofibrillar protein synthesis decreased by approximately 27%, muscle atrophy F-box and myostatin mRNA expression were upregulated, whereas mechanistic target of rapamycin, p53, and PDK4 mRNA expression were downregulated after step reduction.

PRACTICAL TAKE AWAY - just one week of sedentary lifestyle substantially lowered daily myofibrillar protein synthesis rates.

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