RESEARCH: Studies reviewed this week: 04 October 2021 to 10 October 2021

NUTRITION: Beneficial metabolic adaptations due to endurance exercise training in the fasted state

Training in a low-CHO state can have its benefits, however, it is important to make sure you don't do it too frequently (see this study). Nevertheless there are some benefits to this training protocol as investigated by this study; the authors investigated "the effect of consistent training in the fasted state, vs training in the fed state, on muscle metabolism and substrate selection during fasted exercise". The protocol they used was:

Twenty young male volunteers participated in a 6-wk endurance training program (1–1.5 h cycling at 70% V˙ O2max, 4 days/wk) while receiving isocaloric carbohydrate-rich diets. Half of the subjects trained in the fasted state (F), while the others ingested ample carbohydrates before (160 g) and during (1 g·kg body wt1 ·h1 ) the training sessions.

The results showed that:

Consistent exercise training in the fasted state markedly stimulates the contribution of IMCL to energy provision during fasting endurance exercise. Fasting training also increases muscular oxidative capacity more than a similar intensity and duration of exercise with ample exogenous carbohydrate supply.
Regular fasted training is a useful strategy to stimulate physiological adaptations in muscle that may eventually contribute to improve endurance exercise performance.

PRACTICAL TAKEAWAY - there are benefits to training in a fasted state (be careful how frequently you apply this protocol).

HRV: Heart Rate Variability-Guided Training for Enhancing Cardiac-Vagal Modulation, Aerobic Fitness, and Endurance Performance

In this review and meta analysis of HRV-guided training the authors found that:

HRV-guided training was superior for enhancing vagal-related HRV indices, but not resting HR.
Consistently small but non-significant SMDs in favor of HRV-guided training were observed for enhancing maximal aerobic capacity, aerobic capacity at second ventilatory threshold, and endurance performance.

This led the authors to conclude:

HRV-guided training may be more effective than predefined training for maintaining and improving vagal-mediated HRV, with less likelihood of negative responses. However, if HRV-guided training is superior to predefined training for producing group-level improvements in fitness and performance, current data suggest it is only by a small margin.

PRACTICAL TAKEAWAY - HRV-guided training can provide small improvements and benefits for training optimisation.

LOAD: Peer Presence Increases Session Ratings of Perceived Exertion

RPE is a fantastic metric to track as it's free and always available. I've shared many different studies about using RPE (see resources page) and they're all positive. However, understanding the nuances of measurement is important and in this study the authors chose to test "the effect of peer presence on session rating of perceived exertion (RPE) responses". They found that:

Session-RPE was voted higher when collected in the group’s presence compared with when written.
Session-RPE was not different between the group and verbal, or verbal and written collection contexts.

The authors conclude that:

This study suggests that contextual psychosocial inputs influence session-RPE and highlights the importance of session-RPE users controlling the measurement environment when collecting votes.

PRACTICAL TAKEAWAY - make sure to measure RPE in a consistent manner while being mindful of other factors such as peer pressure that can lead to inconsistent values.

NUTRITION: Nitrate-rich beetroot juice ingestion reduces skeletal muscle O2 uptake and blood flow during exercise in sedentary men

This study set out to extend the research on nitrate supplementation from current state of understanding around pulmonary O2 uptake and exercise performance to muscle O2 uptake. The authors set out to determine "the effects of nitrate supplementation on local metabolic and hemodynamic regulation in contracting human skeletal muscle". The findings show positive results in terms of muscle O2 demand:

By using leg exercise engaging a small muscle mass, we show that O2 uptake and blood flow are similarly reduced in contracting skeletal muscle of humans during exercise.
Nitrate and nitrite concentrations are reduced across the exercising leg, suggesting that these ions are extracted from the arterial blood by contracting skeletal muscle.

However, this change in uptake of O2 in the muscles did not show performance benefits:

Nitrate supplementation does not enhance muscle VO2 kinetics during exercise, nor does it improve time to exhaustion when exercising with a small muscle mass.

PRACTICAL TAKEAWAY - there are definitely changes in muscle O2 demand when nitrate supplementation is used, but it doesn't appear to improve performance at this stage.

PHYSIOLOGY: The effect of elevated muscle pain on neuromuscular fatigue during exercise

This fascinating study set out to understand the mechanisms that cause fatigue due to muscle pain. The authors explain what they're trying to understand quite clearly:

Previous work has found that in combination with traditional physiological parameters (e.g. lactate threshold), pain tolerance (i.e. the maximum level of perceived pain someone can tolerate) can partially predict cycling time-trial performance and that reducing muscle pain through the ingestion of acetaminophen results in an improvement in endurance performance. Conversely, elevating muscle pain through the intramuscular injection of hypertonic saline has been shown to reduce isometric TTF performance and maximum muscle strength. The mechanisms which underpin these changes are suggested to be centrally mediated but the fatiguing effect of pain during exercise is unclear.

The study showed significant decreases in both endurance and strength when additional muscle pain was enduced:

Time-to-task failure (TTF) was reduced in the participants with additional enduced muscle pain compared to the control group...and...maximum voluntary force was 12% lower at minute 1 and 11% lower at minute 2 compared to the control group.

The authors conclude that:

Muscle pain reduces exercise performance through the excacerbation of neuromuscular fatigue that is central in origin. This appears to be from inhibitory feedback from group III/IV nociceptors which acts to reduce central motor output.

PRACTICAL TAKEAWAY - muscle pain leads to additional fatigue and poorer performance. In situations where training can prepare an athlete in a way that reduces pain during performance (eg downhill training for a mountainous trail race) there is likely to be a significant performance benefit.

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