Friday, March 8, 2013

Applied Physiology: what's new?

Girard et al (2013). Hot conditions improve power output during repeated cycling sprints without modifying neuromuscular fatigue characteristics. Eur J Appl Physiol 113(2): 359-369
ASPETAR, Qatar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
This study investigated the effect of hot conditions on repeated sprint cycling performance and post-exercise alterations in isometric knee extension function. Twelve physically active participants performed 10 × 6-s "all-out" sprints on a cycle ergometer (recovery = 30 s), followed 6 min later by 5 × 6-s sprints (recovery = 30 s) in either a neutral (24 °C/30 %rH) or a hot (35 °C/40 %rH) environment. Neuromuscular tests including voluntary and electrically evoked isometric contractions of the knee extensors were performed before and after exercise. Average core temperature during exercise was higher (38.0 ± 0.1 vs. 37.7 ± 0.1 °C, respectively; P < 0.05) in hot versus neutral environments. Peak power output decreased (-17.9 % from sprint 1 to sprint 10 and -17.0 % from sprint 11 to sprint 15; P < 0.001) across repetitions. Average peak power output during the first ten sprints was higher (+3.1 %; P < 0.01) in the hot ambient temperature condition. Maximal strength (-12 %) and rate of force development (-15 to -26 %, 30-200 ms from the onset of contraction) decreased (P < 0.001) during brief contractions after exercise, irrespectively of the ambient temperature. During brief maximal contractions, changes in voluntary activation (~80 %) were not affected by exercise or temperature. Voluntary activation declined (P < 0.01) during the sustained contraction, with these reductions being more pronounced (P < 0.05) after exercise but not affected by the ambient temperature. Resting twitch amplitude declined (P < 0.001) by ~42 %, independently of the ambient temperature.

Heat exposure has no effect on the pattern and the extent of isometric knee extensor fatigue following repeated cycling sprints in the absence of hyperthermia.
Nybo et al (2012). Markers of muscle damage and performance recovery following exercise in the heat. Med Sci Sports Exerc Dec 14 [Epub ahead of print]

Department of Exercise and Sport Sciences,  University of Copenhagen, Denmark.
ASPETAR, Qatar Orthopaedic and Sports Medicine Hospital, Qatar
Aspire Academy for Sports Excellence, Qatar.

Plasma creatine kinase, serum myoglobin, muscle glycogen and performance parameters (sprint, endurance and neuromuscular testing) were evaluated in 17 semiprofessional soccer players before, immediately after and during 48 h of recovery from a match played in 43°C (HOT) and compared to a control match (21°C with similar turf and set-up). Muscle temperature was ~ 1°C higher (P<0.001) following the game in HOT compared to control, and reached individual values between 39.9 and 41.1°C. Serum myoglobin levels increased by more than 3 fold following the matches (P<0.01), but values were not different in HOT compared to control and they were similar to baseline values following 24 h of recovery. Creatine kinase was significantly elevated both immediately and 24 h after the matches, but the response following HOT was reduced compared to control. Muscle glycogen responses were similar across trials and remained depressed for more than 48 h following both matches. Sprint performance and voluntary muscle activation were impaired to a similar extend following the matches (sprint by ~ 2% and voluntary activation by ~ 1.5%; P<0.05). Both of these performance parameters as well as intermittent endurance capacity (estimated by a Yo-Yo IR1 test) were fully recovered 48 h after both matches.

Environmental heat stress does not aggravate the recovery response from competitive intermittent exercise associated with elevated muscle temperatures and markers of muscle damage, delayed resynthesis of muscle glycogen and impaired post-match performance.
Areta et al. (2013). Timing and distribution of protein ingestion during prolonged recovery from resistamce exercise alters myofibrillar protein synthesis. J Physiol March 4 [Epub ahead of print]
RMIT University, Australian Institute of Sport, McMaster University & Nestle Research Center

Quantity and timing of protein ingestion are major factors regulating myofibrillar protein synthesis (MPS). However, the effect of specific ingestion patterns on MPS throughout a 12 h period is unknown. We determined how different distribution of protein feeding during 12 h recovery after resistance exercise affects anabolic responses in skeletal muscle. 24 healthy trained males were assigned to three groups (n=8/group) and undertook a bout of resistance exercise followed by ingestion of 80 g of whey protein throughout 12 h recovery as either: 8x10 g every 1.5 h (PULSE); 4x20 g every 3 h (intermediate: INT); or 2x40 g every 6 h (BOLUS). Muscle biopsies were obtained at rest and after 1, 4, 6, 7 and 12 h post-exercise. Resting and post-exercise MPS (L-[ring-13C6] phenylalanine), and muscle mRNA abundance and cell signalling were assessed. All ingestion protocols increased MPS above rest throughout 1-12 h recovery (88-148%, P<0.02), but INT elicited greater MPS than PULSE and BOLUS (31-48%, P<0.02). In general signalling showed a BOLUS>INT>PULSE hierarchy in magnitude of phosphorylation. MuRF-1 and SLC38A2 mRNA were differentially expressed with BOLUS.  

20 g of whey protein consumed every 3 h was superior to either PULSE or BOLUS feeding patterns for stimulating myofibrillar protein synthesis throughout the day.  

Pruscino et al (2013). Effects of compression garments on recovery following intermittent exercise. Eur J Appl Physiol Jan 12 [Epub ahead of print]
Department of Physiology, University of Melbourne, Melbourne, Australia,
The objective of the study was to examine the effects of wearing compression garments for 24 h post-exercise on the biochemical, physical and perceived recovery of highly trained athletes. Eight field hockey players completed a match simulation exercise protocol on two occasions separated by 4 weeks after which lower-limb compression garments (CG) or loose pants (CON) were worn for 24 h. Blood was collected pre-exercise and 1, 24 and 48 h post-exercise for IL-6, IL-1β, TNF-α, CRP and CK. Blood lactate was monitored throughout exercise and for 30 min after. A 5 counter-movement jump (5CMJ) and squat jump were performed and perceived soreness rated at pre-exercise and 1, 24 and 48 h post-exercise. Perceived recovery was assessed post-exercise using a questionnaire related to exercise readiness. Repeated measures ANOVA was used to assess changes in blood, perceptual and physical responses to recovery. CK and CRP were significantly elevated 24 h post-exercise in both conditions (p < 0.05). No significant differences were observed for TNF-α, IL1-β, IL-6 between treatments (p > 0.05). Power and force production in the 5CMJ was reduced and perceived soreness was highest at 1 h post-exercise (p < 0.05). Perceived recovery was lowest at 1 h post-exercise in both conditions (p < 0.01), whilst overall, perceived recovery was greater when CG were worn (p < 0.005).

None of the blood or physical markers of recovery indicates any benefit of wearing compression garments post-exercise. However, muscle soreness and perceived recovery indicators suggest a psychological benefit may exist.

Beaven et al (2012). Intermittent lower-limb occlusion enhances recovery after strenuous exercise. Appl Physiol Nutr Metab, 37(6): 1132-9
United Kingdom Sports Council, London, UK.

Repeated cycles of vascular occlusion followed by reperfusion initiate a protective mechanism that acts to mitigate future cell injury. Such ischemic episodes are known to improve vasodilation, oxygen utilization, muscle function, and have been demonstrated to enhance exercise performance. Thus, the use of occlusion cuffs represents a novel intervention that may improve subsequent exercise performance. Fourteen participants performed an exercise protocol that involved lower-body strength and power tests followed by repeated sprints. Occlusion cuffs were then applied unilaterally (2 × 3-min per leg) with a pressure of either 220 (intervention) or 15 mm Hg (control). Participants immediately repeated the exercise protocol, and then again 24 h later. The intervention elicited delayed beneficial effects (24 h post-intervention) in the countermovement jump test with concentric (effect size (ES) = 0.36) and eccentric (ES = 0.26) velocity recovering more rapidly compared with the control. There were also small beneficial effects on 10- and 40-m sprint times. In the squat jump test there were delayed beneficial effects of occlusion on eccentric power (ES = 1.38), acceleration (ES = 1.24), and an immediate positive effect on jump height (ES = 0.61).

Specific beneficial effects on recovery of power production and sprint performance were observed both immediately and 24 h after intermittent unilateral occlusion was applied to each leg.

Samuels (2012) Jet lag and travel fatigue: a comprehensive management plan for sport medicine physicians and high-performance support teams. Clin J Sport Med 22(3): 268-273

Centre for Sleep and Human Performance, Calgary, Canada.

The impact of transcontinental travel and high-volume travel on athletes can result in physiologic disturbances and a complicated set of physical symptoms. Jet lag and travel fatigue have been identified by athletes, athletic trainers, coaches, and physicians as important but challenging problems that could benefit from practical solutions. Currently, there is a culture of disregard and lack of knowledge regarding the negative effects of jet lag and travel fatigue on the athlete's well-being and performance. In addition, the key physiologic metric (determination of the human circadian phase) that guides jet lag treatment interventions is elusive and thus limits evidence-based therapeutic advice. A better understanding of preflight, in-flight, and postflight management options, such as use of melatonin or the judicious application of sedatives, is important for the sports clinician to help athletes limit fatigue symptoms and maintain optimal performance. The purpose of this article was to provide a practical applied method of implementing a travel management program for athletic teams.

American Journal of Physiology
Applied Physiology Nutrition and Metabolism
Clinical Sports Medicine
European Journal of Applied Physiology
Journal of Physiology
Medicine & Science in Sport & Exercise

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