Integrating Heat Training in the Rehabilitation Toolbox for the Injured Athlete

Resistance Training in the Heat: Mechanisms of Hypertrophy and Performance Enhancement

ABSTRACT

Pryor, JL, Sweet, D, Rosbrook, P, Qiao, J, Hess, HW, and Looney, DP. Resistance training in the heat: Mechanisms of hypertrophy and performance enhancement. J Strength Cond Res 38(7): 1350-1357, 2024-The addition of heat stress to resistance exercise or heated resistance exercise (HRE) is growing in popularity as emerging evidence indicates altered neuromuscular function and an amplification of several mechanistic targets of protein synthesis. Studies demonstrating increased protein synthesis activity have shown temperature-dependent mammalian target of rapamycin phosphorylation, supplemental calcium release, augmented heat shock protein expression, and altered immune and hormone activity. These intriguing observations have largely stemmed from myotube, isolated muscle fiber, or rodent models using passive heating alone or in combination with immobilization or injury models. A growing number of translational studies in humans show comparable results employing local tissue or whole-body heat with and without resistance exercise. While few, these translational studies are immensely valuable as they are most applicable to sport and exercise. As such, this brief narrative review aims to discuss evidence primarily from human HRE studies detailing the neuromuscular, hormonal, and molecular responses to HRE and subsequent strength and hypertrophy adaptations. Much remains unknown in this exciting new area of inquiry from both a mechanistic and functional perspective warranting continued research.

Exercise responses to heart rate clamped cycling with graded blood flow restriction

OBJECTIVES

To quantify the acute effects of graded blood flow restriction on the interaction between changes in mechanical output, muscle oxygenation trends and perceptual responses to heart rate clamped cycling.

DESIGN

Repeated measures.

METHODS

Twenty-five adults (21 men) performed six, 6-min cycling bouts (24 min of recovery) at a clamped heart rate corresponding to their first ventilatory threshold at 0 % (unrestricted), 15 %, 30 %, 45 %, 60 % and 75 % of arterial occlusion pressure with the cuffs inflated bilaterally from the fourth to the sixth minute. Power output, arterial oxygen saturation (pulse oximetry) and vastus lateralis muscle oxygenation (near-infrared spectroscopy) were monitored during the final 3 min of pedalling, whilst perceptual responses (modified Borg CR10 scales) were obtained immediately after exercise.

RESULTS

Compared to unrestricted cycling, average power output for minutes 4-6 decreased exponentially for cuff pressures ranging 45-75 % of arterial occlusion pressure (P < 0.001). Peripheral oxygen saturation averaged ∼96 % across all cuff pressures (P = 0.318). Deoxyhemoglobin changes were larger at 45-75 % versus 0 % of arterial occlusion pressure (P < 0.05), whereas higher total haemoglobin values occurred at 60-75 % of arterial occlusion pressure (P < 0.05). Sense of effort, ratings of perceived exertion, pain from cuff pressure, and limb discomfort were exaggerated at 60-75 % versus 0 % of arterial occlusion pressure (P < 0.001).

CONCLUSIONS

Blood flow restriction of at least 45 % of arterial occlusion pressure is required to reduce mechanical output during heart rate clamped cycling at the first ventilatory threshold. Whilst power decreases non-linearly above this pressure threshold, higher occlusion levels ranging 60-75 % of arterial occlusion pressure also accentuate muscle deoxygenation and exercise-related sensations.

Skeletal muscle oxidative adaptations following localized heat therapy

Repeated heat treatment has been shown to induce oxidative adaptations in cell cultures and rodents, but similar work within human models is scarce. This study investigated the effects of 6 weeks of localized heat therapy on near-infrared spectroscopy-(NIRS) derived indices of muscle oxidative and microvascular function. Twelve physically active participants (8 males and 4 females, age: 34.9 ± 5.9 years, stature: 175 ± 7 cm, body mass: 76.7 ± 13.3 kg) undertook a 6-week intervention, where adhesive heat pads were applied for 8 h/day, 5 days/week, on one calf of each participant, while the contralateral leg acted as control. Prior to and following the intervention, the microvascular function was assessed using NIRS-based methods, where 5 min of popliteal artery occlusion was applied, and the reperfusion (i.e., re-saturation rate, re-saturation amplitude, and hyperemic response) was monitored for 2 min upon release. Participants also performed a 1-min isometric contraction of the plantar flexors (30% maximal voluntary contraction), following which a further 2 min interval was undertaken for the assessment of recovery kinetics. A 20-min time interval was allowed before the assessment protocol was repeated on the contralateral leg. Repeated localized heating of the gastrocnemius did not influence any of the NIRS-derive indices of microvascular or oxidative function (p > 0.05) following 6 weeks of treatment. Our findings indicate that localized heating via the use of adhesive heat pads may not be a potent stimulus for muscle adaptations in physically active humans.

Effect of heat acclimation on metabolic adaptations induced by endurance training in soleus rat muscle

Aerobic training leads to well‐known systemic metabolic and muscular alterations. Heat acclimation may also increase mitochondrial muscle mass. We studied the effects of heat acclimation combined with endurance training on metabolic adaptations of skeletal muscle. Thirty‐two rats were divided into four groups: control (C), trained (T), heat‐acclimated (H), and trained with heat acclimation (H+T) for 6 weeks. Soleus muscle metabolism was studied, notably by the in situ measurement of mitochondrial respiration with pyruvate (Pyr) or palmitoyl‐coenzyme A (PCoA), under phosphorylating conditions (V˙max) or not (V˙0). Aerobic performance increased, and retroperitoneal fat mass decreased with training, independently of heat exposure (p < 0.001 and p < 0.001, respectively). Citrate synthase and hydroxyl‐acyl‐dehydrogenase activity increased with endurance training (p < 0.001 and p < 0.01, respectively), without any effect of heat acclimation. Training induced an increase of the V˙0 and V˙max for PCoA (p < .001 and p < .01, respectively), without interference with heat acclimation. The training‐induced increase of V˙0 (p < 0.01) for pyruvate oxidation was limited when combined with heat acclimation (−23%, p < 0.01). Training and heat acclimation independently increased the V˙max for pyruvate (+60% p < 0.001 and +50% p = 0.01, respectively), without an additive effect of the combination. Heat acclimation doubled the training effect on muscle glycogen storage (p < 0.001). Heat acclimation did not improve mitochondrial adaptations induced by endurance training in the soleus muscle, possibly limiting the alteration of carbohydrate oxidation while not facilitating fatty‐acid utilization. Furthermore, the increase in glycogen storage observed after HA combined with endurance training, without the improvement of pyruvate oxidation, appears to be a hypoxic metabolic phenotype.

The Use of Recovery Strategies in Professional Soccer: A Worldwide Survey

PURPOSE

To survey soccer practitioners' recovery strategy: (1) use, (2) perceived effectiveness, and (3) factors influencing their implementation in professional soccer.

METHODS

A cross-sectional convenience sample of professional soccer club/confederation practitioners completed a web-based survey (April to July 2020). Pearson chi-square and Fisher exact tests with Cramer V (φ - c) assessed relationships and their strength, respectively, between the perceived effectiveness and frequency of strategy use.

RESULTS

A total of 80 soccer practitioners (13 countries) completed the survey. The 3 most important recovery objectives were "alleviating muscle damage/fatigue," "minimizing injury risk," and "performance optimization." The most frequently used strategies were active recovery, structured recovery day, extra rest day, massage, cold-water therapy, and carbohydrate provision (predominantly on match day and match day + 1). Relationships were identified between perceived effectiveness and frequency of strategy use for sleep medication (P < .001, φ - c = 0.48), carbohydrate provision (P = .007, φ - c = 0.60), protein provision (P = .007, φ - c = 0.63), an extra rest day (P < .001, φ - c = 0.56), and a structured recovery day (P = .049, φ - c = 0.50).

CONCLUSIONS

The study demonstrates that professional soccer practitioners have a range of objectives geared toward enhancing player recovery. A disconnect is apparent between the perceived effectiveness of many recovery strategies and their frequency of use in an applied setting. Novel data indicate that strategies are most frequently employed around match day. Challenges to strategy adoption are mainly competing disciplinary interests and resource limitations. Researchers and practitioners should liaise to ensure that the complexities involved with operating in an applied environment are elucidated and apposite study designs are adopted, in turn, facilitating the use of practically effective and compatible recovery modalities.

The influence of environmental and core temperature on cyclooxygenase and PGE2 in healthy humans

Whether cyclooxygenase (COX)/prostaglandin E2 (PGE2) thermoregulatory pathways, observed in rodents, present in humans? Participants (n = 9) were exposed to three environments; cold (20 °C), thermoneutral (30 °C) and hot (40 °C) for 120 min. Core (Tc)/skin temperature and thermal perception were recorded every 15 min, with COX/PGE2 concentrations determined at baseline, 60 and 120 min. Linear mixed models identified differences between and within subjects/conditions. Random coefficient models determined relationships between Tc and COX/PGE2. Tc [mean (range)] increased in hot [+ 0.8 (0.4-1.2) °C; p < 0.0001; effect size (ES): 2.9], decreased in cold [- 0.5 (- 0.8 to - 0.2) °C; p < 0.0001; ES 2.6] and was unchanged in thermoneutral [+ 0.1 (- 0.2 to 0.4) °C; p = 0.3502]. A relationship between COX2/PGE2 in cold (p = 0.0012) and cold/thermoneutral [collapsed, condition and time (p = 0.0243)] was seen, with higher PGE2 associated with higher Tc. A within condition relationship between Tc/PGE2 was observed in thermoneutral (p = 0.0202) and cold/thermoneutral [collapsed, condition and time (p = 0.0079)] but not cold (p = 0.0631). The data suggests a thermogenic response of the COX/PGE2 pathway insufficient to defend Tc in cold. Further human in vivo research which manipulates COX/PGE2 bioavailability and participant acclimation/acclimatization are warranted to elucidate the influence of COX/PGE2 on Tc.