RESEARCH: studies I shared this week: 31 October to 6 November 2022

All of the studies I've shared (~500 studies) are available on the RESOURCES PAGE.

HEAT: Heat suit training increases hemoglobin mass in elite cross‐country skiers

STUDY DETAILS -

1. Twenty-five male XC skiers were divided into a group that added 5x50 min weekly heat suit training sessions to their regular training or to a control group matched for training volume and intensity distribution.
2. HEAT led to 30 g greater Hbmass and 157 mL greater red blood cell volume post-intervention, compared to CON when adjusted for baseline values.
3. In contrast, no group differences were observed for changes in work economy, running velocity, and fractional utilization of maximal oxygen uptake (V̇O2max ) at 4 mmol·L-1 blood lactate, V̇O2max or 15-min running distance performance trial during the intervention.

PRACTICAL TAKEAWAY - heat-suit training improved physiological markers, but didn't appear to improve performance.

HRV: a biomarker to study the influence of nutrition on physiological and psychological health?

STUDY DETAILS -

1. Reduced HRV is associated with the development of numerous conditions for example, diabetes, cardiovascular disease, inflammation, obesity and psychiatric disorders.
2. In a healthy sample, Meule et al. (2012b) found that restrained eating, which is the intentional restriction of food intake to prevent weight gain or to promote weight loss, was associated with low cardiac vagal control.
3. In a further study, Meule et al. (2012a) qualified this finding by considering successful versus unsuccessful dieters: success was associated positively with HF-HRV.
4. These associations between eating behaviour and HRV offer the possibility of examining the association between the ability of different types of food to influence HRV and their ability to reduce or prevent pathological eating behaviours.
5. An increasing number of studies report that particular foods, nutrients and dietary styles influence HRV, supporting its future use when examining the impact of what we eat.

PRACTICAL TAKEAWAY - HRV may be a useful variable for studying dietary interventions.

HEAT: Exertional heat stroke in sport and the military

STUDY DETAILS -

1. Exertional heat illness occurs along a continuum, developing from the relatively mild condition of muscle cramps, to heat exhaustion, and in some cases to the life-threatening condition of heat stroke.
2. The development of exertional heat stroke (EHS) is associated with an increase in core temperature stemming from inadequate heat dissipation to offset the rate of metabolically generated heat.
3. In athletes, individual susceptibility to EHS is dependent on several intrinsic and extrinsic factors, including environmental, individual and organisational factors, health conditions, medication and drug use, and behavioural responses.
4. EHS is the second most common cause of non-traumatic death in competitive athletes.
5. Along with the prevailing environmental conditions, the prevalence of EHS is related to the demands of the sport (i.e., individual or team), such as exercise duration, intensity, clothing, and rules and regulations (e.g., rest and hydration breaks).
6. Heat acclimation and acclimatisation, which refer to periods of repeated heat exposure in artificial (i.e., laboratory) and natural (i.e., outdoor) settings, respectively, lead to physiological and molecular adaptations that reduce the deleterious effects of heat stress and reduce exertional heat illness susceptibility.
7. It is also recommended to ensure euhydration before exercise and replace a portion of sweat losses during exercise if possible, to mitigate the compounding effects of hyperthermia and dehydration.
8. Other mitigation strategies include pre- and per-cooling, and ensuring adequate sleep.

PRACTICAL TAKEAWAY - if you are planning to race in a hot environment, acclimate before hand and then ensure you hydrate well, sleep well before the event, and if possible follow cooling practices.

PHYSIOLOGY: Slow postmeal walking reduces postprandial glycemia in middle-aged women

STUDY DETAILS -

1. Postprandial blood glucose concentration is a risk factor for the development of cardiovascular diseases and diabetes, even at states well below hyperglycemic levels.
2. The objective of the present study was to examine whether even postmeal slow walking would have a similar effect.
3. We conclude that even slow postmeal walking can reduce the blood glucose response to a carbohydrate-rich meal. The magnitude of this effect seems to be related to the duration of walking and to the magnitude of the postprandial blood glucose response when resting after a carbohydrate-rich meal.

PRACTICAL TAKEAWAY - going for a walk, even very slowly, can help reduce the blood glucose response to a CHO-rich meal.

NUTRITION: Patterns of energy availability of free-living athletes display day-to-day variability that is not reflected in laboratory-based protocols

STUDY DETAILS -

1. The physiological effects of low energy availability (EA) have been studied using a homogenous daily EA pattern in laboratory settings. However, whether this daily EA pattern represents those of free-living athletes and is therefore ecologically valid is unknown.
2. we assessed daily exercise energy expenditure, energy intake and EA in 10 free-living elite male road cyclists during 7 consecutive days of late pre-season training.
3. Within-participants correlation between daily energy intake and exercise energy expenditure was .62, and .60 between carbohydrate intake and exercise energy expenditure.
4. However, energy intake only partially compensated for exercise energy expenditure, increasing 210 kcal · day−1 per 1000 kcal · day−1 increase in expenditure.

PRACTICAL TAKEAWAY - periodized nutrition is important to avoid low energy availability on big days.

We had a good discussion on Twitter about this and what time frame to measure to understand EA balance.

TRAINING: Effects of high-intensity interval training with hyperbaric oxygen

STUDY DETAILS -

1. Hyperbaric Oxygen (HBO2) has been proposed as a pre-conditioning method to enhance exercise performance.
2. We hypothesized that HBO2 could enhance aerobic capacity by inducing mitochondrial biogenesis via redox signaling in skeletal muscle.
3. HBO2 was administered in combination with high-intensity interval training (HIIT), a potent redox stimulus known to induce mitochondrial biogenesis.
4. Each completed 6 HIIT sessions over 2 weeks randomized to breathing normobaric air, "HIIT+Air" (PiO2 = 0.21 ATM) or HBO2 (PiO2 = 1.4 ATM) during training, "HIIT+HBO2" group.
5. When combined with HIIT, short-term modest HBO2 (1.4 ATA) has does not increase whole-body V̇O2peak during acute hypobaric hypoxia

PRACTICAL TAKEAWAY - using hypobaric oxygen does not appear to enhance the benefits of HIIT training.