Warm-up practices in elite snowboard athletes.

PURPOSE: The purpose of this project was to observe current warm-up practices in snowboard athletes and evaluate their physiological impact before competition. METHODS: An observational design was used to monitor 4 athletes (2 female) at an Open National Snowboard Cross Championships. Activity patterns, core temperature, heart rate (HR), and time between warm-up and competition were measured. Athlete ratings of thermal comfort (TC) and thermal sensation (TS) were recorded before competition. RESULTS: Significant barriers and challenges to an optimal warm-up included delays, environment, and logistics. Time gaps between structured warm-up and competition start time were in excess of 1 h (median=68.8 min). Median average HR for 10 min (HR10) did not exceed 120 beats/min in the hour preceding competition, suggesting a suboptimal warm-up intensity. Athletes rated their TC between comfortable and slightly uncomfortable and TS as neutral to slightly warm before the start of qualifications and finals. CONCLUSIONS: The observations of this project suggest significant gaps in current warm-up strategies used in snowboarding. These include inadequate general aerobic warm-up (based on intensity and duration), excessive time between warm-up and competition, and lack of a consistent and structured warm-up protocol. Future work is needed to evaluate the effectiveness of different warm-up strategies on muscle temperature and performance while determining the optimal length of time between warm-up and competition.

Prefrontal cortex oxygenation is preserved and does not contribute to impaired neuromuscular activation during passive hyperthermia.

We investigated the role of passive hyperthermia upon motor unit activation and prefrontal cortex oxygenation. Six healthy males were passively heated, using a liquid conditioning garment in a hot environment (35 degrees C, 50% relative humidity). Maximal force output and voluntary activation were examined during a 10 s maximal isometric knee extension. Of the initial 6 subjects, 1 experienced syncope at a rectal temperature (Tre) of 38.0 degrees C and was removed from the study. The remaining 5 subjects completed heating and testing to a Tre of 38.5 degrees C (n = 1), 39.0 degrees C (n = 3), or 39.5 degrees C (n = 1), and then were cooled back to baseline. Force production decreased from 553 +/- 133 to 430 +/- 176 N (p < 0.01) with passive heating, as did voluntary activation (from 90 +/- 5% to 84 +/- 7%). Percent heart rate reserve increased from 8 +/- 5% to 59 +/- 3% before returning to 4 +/- 8% (p < 0.001). Although mean arterial pressure remained unchanged, there were significant decreases in diastolic blood pressure with heating (80 +/- 3 to 63 +/- 8 mm Hg). Passive heating did not alter prefrontal cortex oxygenation, but cooling back to baseline core temperature attenuated cerebral oxygenated and total hemoglobin levels (p < 0.05). Passive heating to the point of voluntary exhaustion elevated cardiovascular and thermal strain and subjective perceptions of thermal discomfort. However, while this resulted in a marked decrement in maximal isometric force production and central voluntary activation, no concomitant changes in cerebral oxygenation were observed, suggesting that overall cerebrovascular regulation was maintained.

Hypervolemia and blood alkalinity: effect on physiological strain in a warm environment.

PURPOSE: To evaluate the influence of acute hypervolemia, achieved through the ingestion of a sodium citrate-rich beverage, on cardiovascular strain and thermoregulatory function, during moderate-intensity aerobic exercise in a warm environment. Sodium citrate's ability to increase buffering capacity was also assessed. METHODS: Twelve endurance-trained athletes completed two blind randomized treatment trials, separated by a minimum of seven days, on a cycle ergometer under heat stress (30.9 degrees C, 64% RH). The subjects ingested 12 mL.kg(-1) of (1) Gatorade, the control (CNT), or (2) sodium-citrate plus Gatorade (NaCIT: 170 mmol Na+L(-1)) before cycling at 15% below ventilatory threshold (VT) for 62 minutes. Core and skin temperature, expired gas samples, heart rate, and perceived exertion were measured throughout exercise. Blood samples were taken before drinking each beverage, before commencing exercise, and throughout the exercise bout. RESULTS: Plasma volume (PV) was significantly expanded in the NaCIT trial (3.6+/-5.5%) and remained significantly higher throughout exercise in the NaCIT trial compared with the CNT trial (P

Effects of varying post-warm-up recovery time on 200-m time-trial swim performance.

CONTEXT: Warm-up before athletic competition might enhance performance by affecting various physiological parameters. There are few quantitative data available on physiological responses to the warm-up, and the data that have been reported are inconclusive. Similarly, it has been suggested that varying the recovery period after a standardized warm-up might affect subsequent performance. PURPOSE: To determine the effects of varying post-warm-up recovery time on a subsequent 200-m swimming time trial. METHODS: Ten national-caliber swimmers (5 male, 5 female) each swam a 1500-m warm-up and performed a 200-m time trial of their specialty stroke after either 10 or 45 min of passive recovery. Subjects completed 1 time trial in each condition separated by 1 wk in a counterbalanced order. Blood lactate and heart rate were measured immediately after warm-up and 3 min before, immediately after, and 3 min after the time trial. Rating of perceived exertion was measured immediately after the warm-up and time trial. RESULTS: Time-trial performance was significantly improved after 10 min as opposed to 45 min recovery (136.80 +/- 20.38 s vs 138.69 +/- 20.32 s, P < .05). There were no significant differences between conditions for heart rate and blood lactate after the warm-up. Pre-time-trial heart rate, however, was higher in the 10-min than in the 45-min rest condition (109 +/- 14 beats/min vs 94 +/- 21 beats/min, P < .05). CONCLUSIONS: A post-warm-up recovery time of 10 min rather than 45 min is more beneficial to 200-m swimming time-trial performance.

Using microtechnology to monitor thermal strain and enhance performance in the field.

Wireless microtechnologies are rapidly emerging as useful tools for sport scientists to move their work out of the laboratory and into the field. The purpose of this report is to describe some of the practical aspects of using ingestible radiotelemetric temperature sensors in sport physiology. Information is also presented to demonstrate the utility of this technology in understanding individual differences in coping with environmental stress, optimizing heat adaptation, and fine-tuning competition strategy (pacing). Wireless core-temperature technology has already revolutionized field monitoring of elite athletes training and competing in extreme environments. These technologies are valuable tools for sport scientists to better understand the interaction between the physiology of exercise and the environment.

Aerobic influence on neuromuscular function and tolerance during passive hyperthermia.

PURPOSE: To determine the role of aerobic fitness on central neuromuscular activation and maximal voluntary contractile force during hyperthermia. METHODS: Thirty-seven healthy males in three distinct groups based on aerobic fitness and training history were passively heated using a liquid conditioning garment in a hot (35 degrees C, 50% RH) environment with the intention of testing neuromuscular function with whole-body hyperthermia. Of these initial participants, 11 of the 13 highly fit (HF; VO2max = 71.2 +/- 5.9 mL x kg(-1) x min(-1), body fat = 5.6 +/- 1.9%), 11 of the 13 moderately fit (MF; 57.2 +/- 4.2 mL x kg(-1) x min(-1), 11 +/- 3.4%), and 4 of the 11 lower-fit (LF; 49.6 +/- 1.1 mL x kg(-1) x min(-1), 19.4 +/- 2.6%) individuals tolerated heating to 39.0 degrees C, with the remainder terminating the experimental protocol early. Maximal force output and voluntary activation were examined during a 10-s maximal isometric knee extension. RESULTS: Passive heating attenuated force production (-61.7 +/- 69.6 N change from initial values) and decreased voluntary activation (8.6 (12.6), 18.1 (12.4), and 6.1 (3.1)% for HF, MF, and LF training groups, respectively). Cardiovascular strain moderately increased to 60 +/- 14% (P < 0.001), whereas HF and MF had significantly higher MAP than LF at the end of heating (98 +/- 15, 99 +/- 7, and 79 +/- 5 mm Hg for HF, MF, and LF, respectively; P < 0.05). However, the ability to tolerate passive heating to 39.0 degrees C (and above) differed between the HF and MF compared with LF, despite no difference in their psychophysical rankings of thermal sensations and/or (dis)comfort. CONCLUSION: Low aerobic fitness and activity level are associated with a decreased tolerance to passive hyperthermia. However, at high body temperatures, maximum force production and voluntary activation were impaired to an equal level regardless of training status.

Central and peripheral factors in thermal, neuromuscular, and perceptual adaptation of the hand to repeated cold exposures.

We investigated the role of central and peripheral factors in repeated cold exposure of the hand and their effects on temperature response, neuromuscular function, and subjective thermal sensation. Eleven subjects immersed their left hand repeatedly in 8 degrees C cold water for 30 min, 5 d/week, for 2 weeks. Before and following the 2 weeks of exposure, neuromuscular function, blood markers, thermal sensation, and temperature responses of both acclimated (left) and control (right) hands were tested. Minimum index finger temperature pre-acclimation was 10.9 +/- 3.4 degrees C and 10.0 +/- 2.0 degrees C in the left and right hand, respectively, and did not change significantly post-acclimation (left, 12.8 +/- 4.2 degrees C; right, 10.2 +/- 1.1 degrees C). Neuromuscular function was impaired with cooling, but this was significantly different neither between the hands nor over time. Central factors, measured by catecholamines and changes in temperature and cardiovascular response over time, did not change and there were no differences in responses between the exposed and non-exposed hand over time (peripheral adaptation) nor were there any differences in local factors endothelial-1 and nitric oxide. Subjective thermal comfort was improved and the discrepancy that was found between the change in actual and perceived temperature may increase the risk of cold injury in partially acclimatized individuals, owing to an adjustment in behavioural thermoregulation.

Voluntary muscle activation is impaired by core temperature rather than local muscle temperature.

Fatigue during hyperthermia may be due in part to a failure of the central nervous system to fully activate the working muscles. We investigated the effects of passive hyperthermia on maximal plantar flexor isometric torque (maximal isometric voluntary contraction) and voluntary activation to determine the roles of local skin temperature, core temperature, and peripheral muscle temperature in fatigue. Nine healthy subjects were passively heated from 37.2 to 39.5 degrees C (core temperature) and then cooled back down to 37.9 degrees C using a liquid-conditioning garment, with the right leg kept at a thermoneutral temperature throughout the protocol, whereas the left leg was allowed to heat and cool. Passive heating resulted in significant decreases in torque from [mean (SD)] 172 N x m (SD 39) to 160 N x m (SD 44) and in voluntary activation from 96% (SD 2) to 91% (SD 5) in the heated leg, and maximal isometric voluntary contraction decreased similarly from 178 N xm (SD 37) to 165 N x m (SD 38) and voluntary activation from 97% (SD 2) to 94% (SD 5) in the thermoneutral leg. The initiation of cooling, which produced a rapid decrease in skin temperature and cardiovascular strain [heart rate reserve decreased from 58% (SD 12) to 31% (SD 12)], did not immediately restore either torque or voluntary activation. However, when core temperature was lowered back to normal, torque and voluntary activation were restored to baseline values. It was concluded that an increase in core temperature is a factor responsible for reducing voluntary activation during brief voluntary isometric contractions and that temperature-induced changes in the contractile properties of muscle and local thermal afferent input from the skin do not contribute significantly to the decrement in torque.

Local cold acclimation during exercise and its effect on neuromuscular function of the hand.

Most acclimation research is performed on resting individuals, whereas in real life, cold exposure is often accompanied by physical activity. We examined the effects of 2 weeks of repeated cold exposure of the hand with or without an elevated core temperature from exercise on neuromuscular function of the first dorsal interosseus (FDI) muscle and manual performance of the hand. The experimental group (4 female, 6 male; age, 25.1 +/- 6.9 y) cooled their hands in 8 degrees C water for 30 min daily while cycling (50% of heart rate reserve); the control group (4 female, 4 male; age, 25.1 +/- 5.7 y) remained still. Manual function testing consisted of tactile sensitivity, grip strength, manual dexterity, and evoked twitch force in a custom-made myograph. Thermal sensation, skin temperature of index finger (Tif) and hand (Tfdi), as well as rectal temperature (Tre), were recorded daily. Tre increased significantly during bicycling, by 0.6 +/- 0.2 degrees C. Minimal Tif and Tfdi of the groups combined increased significantly during exposure days from 8.7 +/- 0.7 degrees C and 12.4 +/- 2.8 degrees C to 10.1 +/- 1.3 degrees C and 15.0 +/- 3.0 degrees C, respectively (p=0.04), with no significant difference between groups. Thermal ratings improved significantly on exposure days. Manual function was impaired with cooling, but with no significant difference between groups or across time. Deterioration of twitch characteristics with cooling did not change with repeated cold exposure. Although the increasing core temperature during cold water immersion changed the acute temperature response and thermal ratings, it had no effect on local cold acclimation or manual function.

Effect of cold-induced vasodilatation in the index finger on temperature and contractile characteristics of the first dorsal interosseus muscle during cold-water immersion.

We investigated whether cyclic elevations in index finger temperature (cold-induced vasodilatation, CIVD) during prolonged cold exposure correlated with hand temperature and neuromuscular function. Evoked twitch force of the first dorsal interosseus (FDI) muscle was measured every minute in eight males and four females [age 25.4 (5.7) years, mean (SD)] during cooling of the hand for 30 min in 9 degrees C water, and in thermoneutral 30 degrees C water. During cooling, index finger temperature increased from 9.4 (0.9) degrees C at the nadir to 13.3 (2.4) degrees C (P<0.01) at the apex of the CIVD. However, the minimum skin temperature above the FDI muscle was 14.2 (2.1) degrees C, with no CIVD detected in any of the subjects. Peak twitch force was 2.5 (0.7) N at the nadir of the finger CIVD and 2.0 (0.8) N at the apex (P=0.07), time-to-peak increased from 189 (18) ms to 227 (26) ms (P<0.01), and half relaxation time increased from 135 (14) ms to 183 (32) ms (P<0.01). We conclude that CIVD is a local phenomenon isolated to the fingers, and that it does not have beneficial effects on either temperature or neuromuscular function of the FDI muscle during cold exposure.

Monitoring individual erector spinae fatigue responses using electromyography and near infrared spectroscopy.

This study examined the utility of electromyography and near-infrared spectroscopy (NIRS) in assessing m. erector spinae activity during the Biering-Sorensen Back Muscle Endurance (BSME) test. Six men and four women (27.0 +/- 7.1 years of age) performed the BSME test (time = 131.5 +/- 43.5 s). EMG was used to quantify neuromuscular activity of the right and left side at the L3 level, and root mean square was scaled for maximum value at the start of the exercise. NIRS was used to evaluate blood volume (BV) and oxygenation (OX) simultaneous with EMG bilaterally at the L3 level. There was a decrease to 49+/- 8% of initial median frequency (mean= 83 Hz) on both right and left sides when the exercise was 90% complete, and the slope of the median frequency/time relationship was significantly related to BSME time (r = 0.82). Group means for BV increased during back exercise while OX decreased and was significantly different between right and left sides of the lower back. However, large OX response differences among individuals and between right and left sides were noted. OX and median frequency were moderately related (r = 0.27-0.38). It appears that NIRS combined with EMG is a promising tool for assessing localized metabolic and neuromuscular activity during static contractions of the lower back.

Multiple triggers for hyperthermic fatigue and exhaustion.

It has been proposed that a critical body temperature exists at which muscle activation is impaired through a direct effect of high brain temperature decreasing the central drive to exercise, but other factors may also inhibit performance in the heat. An integrative physiological model is presented to stimulate research into mechanisms of hyperthermic fatigue and exhaustion.

Lowering of skin temperature decreases isokinetic maximal force production independent of core temperature.

Based on studies using maximal isometric contractions, it is suggested that fatigue may be elicited due to hyperthermia-induced impairments in central neuromuscular activation. We investigated the effects of passive hyperthermia on isokinetic maximal force production. Twenty young healthy males [peak oxygen uptake 52.9 (6.8) ml x kg(-1) min(-1), body fat 11 (5)%] were passively warmed in a hot (42 degrees C) water bath to rectal temperature ( T(re)) of 39.5 degrees C and then cooled back to 38.0 degrees C. At 0.5 degrees C intervals, they performed two maximal voluntary knee extensions each at 60, 120, and 240 s(-1). Peak torques at 37.5 degrees C were 168 (34), 145 (29), and 112 (17) N m for 60, 120, and 240 s(-1) contraction speeds, respectively, and 166 (38), 150 (31), and 119 (17) N m at T(re) of 39.5 degrees C. No significant differences in peak torque at any of the three contraction speeds were observed over the range 37.5-39.5 degrees C. Skin cooling, even with a warm core of 39.5 degrees C, immediately decreased peak torque [159 (42), 133 (34), 107 (22) N m at 60, 120, and 240 s(-1), respectively). We conclude that lowered skin temperature can impair isokinetic force production independent of core temperature.

Passive hyperthermia reduces voluntary activation and isometric force production.

It has been suggested that a critically high body core temperature may impair central neuromuscular activation and cause fatigue. We investigated the effects of passive hyperthermia on maximal isometric force production (MVC) and voluntary activation (VA) to determine the relative roles of skin (T(sk)) and body core temperature ( T(c)) on these factors. Twenty-two males [VO(2max)=64.2 (8.9) ml x kg(-1) min(-1), body fat=8.2 (3.9)%] were seated in a knee-extension myograph, then passively heated from 37.4 to 39.4 degrees C rectal temperature (T(re)) and then cooled back to 37.4(o)C using a liquid conditioning garment. Voluntary strength and VA (interpolated twitch) were examined during an isometric 10-s MVC at 0.5 degrees C intervals during both heating and cooling. Passive heating to a T(c) of 39.4(o)C reduced VA by 11 (11)% and MVC by 13 (18)% (P<0.05), but rapid skin cooling, with a concomitant reduction in cardiovascular strain [percentage heart rate reserve decreased from 64 (11)% to 29 (11)%] and psychophysical strain did not restore either of these measures to baseline. Only when cooling lowered T(c) back to normal did VA and MVC return to baseline (P<0.05). We conclude that an elevated T(c) reduces VA during isometric MVC, and neither T(sk) nor cardiovascular or psychophysical strain modulates this response. Results are given as mean (SD) unless otherwise stated.

Temperature effects on the contractile characteristics and sub-maximal voluntary isometric force production of the first dorsal interosseus muscle.

Cooling of a muscle has a detrimental effect on its force, power and contraction velocity, but may improve force control during precision movements by reducing physiological tremor. We investigated if the contractile characteristics of the first dorsal interosseus muscle (FDI) were linked to voluntary force control in warm and hypothermic conditions. Evoked peak twitch force, force at repetitive stimulation of 10 and 20 Hz, and submaximal force control at 25 and 50% maximal voluntary contraction (MVC) of the FDI were measured with cooled [mean (SD); 17.7 (1.3) degrees C] and warm [27.9 (2.3) degrees C] local skin temperatures in six males and four females. With evoked twitches, the time to peak tension was increased after cooling from 161 (38) ms to 219 (34) ms ( P=0.001) and half-relaxation time increased from 94 (24) ms to 157 (46) ms ( P=0.013). Peak force evoked from the repetitive stimulation contraction (10 Hz) increased significantly after cooling from 13.1 (10.2) N to 19.9 (12.1) N ( P=0.026). The coefficient of variation (CV)-representative of the degree of fusion-for evoked repetitive stimulation force (10 Hz) was significantly higher in the warm [3.6 (2.7)%] versus hypothermic condition [2.2 (3.6)%] ( P<0.05). At 25% and 50% MVC, there were no differences in the CV between warm and hypothermic conditions. FDI contractile characteristics change with local cooling, but have little effect upon voluntary submaximal isometric force control. Results are given as mean (SD).

The relationship between maximal jump-squat power and sprint acceleration in athletes.

This study investigated the relationship between sprint start performance (5-m time) and strength and power variables. Thirty male athletes [height: 183.8 (6.8) cm, and mass: 90.6 (9.3) kg; mean (SD)] each completed six 10-m sprints from a standing start. Sprint times were recorded using a tethered running system and the force-time characteristics of the first ground contact were recorded using a recessed force plate. Three to six days later subjects completed three concentric jump squats, using a traditional and split technique, at a range of external loads from 30-70% of one repetition maximum (1RM). Mean (SD) braking impulse during acceleration was negligible [0.009 (0.007) N/s/kg) and showed no relationship with 5 m time; however, propulsive impulse was substantial [0.928 (0.102) N/s/kg] and significantly related to 5-m time ( r=-0.64, P<0.001). Average and peak power were similar during the split squat [7.32 (1.34) and 17.10 (3.15) W/kg] and the traditional squat [7.07 (1.25) and 17.58 (2.85) W/kg], and both were significantly related to 5-m time ( r=-0.64 to -0.68, P<0.001). Average power was maximal at all loads between 30% and 60% of 1RM for both squats. Split squat peak power was also maximal between 30% and 60% of 1RM; however, traditional squat peak power was maximal between 50% and 70% of 1RM. Concentric force development is critical to sprint start performance and accordingly maximal concentric jump power is related to sprint acceleration.

The effects of deer antler velvet extract or powder supplementation on aerobic power, erythropoiesis, and muscular strength and endurance characteristics.

To determine the effects of deer antler velvet on maximal aerobic performance and the trainability of muscular strength and endurance, 38 active males were randomly assigned in a double-blind fashion to either deer antler velvet extract (n = 12), powder (n = 13), or placebo groups (n = 13). Subjects were tested prior to beginning supplementation and a 10-week strength program, and immediately post-training. All subjects were measured for circulating levels of testosterone, insulin-like growth factor, erythropoietin, red cell mass, plasma volume, and total blood volume. Additionally, muscular strength, endurance, and VO2max were determined. All groups improved 6 RM strength equivalently (41 +/- 26%, p < .001), but there was a greater increase in isokinetic knee extensor strength (30 +/- 21% vs. 13 +/- 15%, p = .04) and endurance (21 +/- 19% vs. 7 +/- 12%, p = .02) in the powder compared to placebo group. There were no endocrine, red cell mass or VO2max changes in any group. These findings do not support an erythropoetic or aerobic ergogenic effect of deer antler velvet. Further, the inconsistent findings regarding the effects of deer antler velvet powder supplementation on the development of strength suggests that further work is required to test the robustness of the observation that this supplement enhances the strength training response and to ensure this observation is not a type I error.

Responsiveness of thermal sensors to nonuniform thermal environments and exercise.

BACKGROUND: We investigated the utility of finger temperature, hand heat flux, and mean skin temperature as indices of overall thermal balance during nonuniform thermal manipulations combined with exercise, with a view to identifying useful feedback sites for input into personal thermal control systems. METHODS: There were 16 subjects who performed 4 x 30 s of 120% VO2peak cycling with a 4-min recovery. During recovery, subjects either received no cooling (CON), upper-body cooling (UC), or upper-body cooling combined with leg heating (UCLH) using a multi-zone liquid conditioning garment. Heat loss during recovery was approximately equal to heat production during exercise. Skin temperature was measured on the mid-medial phalanx of the fourth finger. Heat flux was measured on the dorsum of the hand. RESULTS: Neither hand heat flux or finger temperature distinguished between the two cooling conditions during any of the recovery periods, though hand heat flux was very sensitive to the onset and cessation of exercise. Mean skin temperature was significantly different (p < 0.05) during CON (34.0 +/- 0.1 degrees C), UC (32.5 +/- 0.2 degrees C), and UCLH (33.0 +/- 0.2 degrees C). CONCLUSION: Mean skin temperature may serve as a good indicator of overall heat exchange in the body, even when exposed to nonuniform thermal environments. As hand heat flux was very sensitive to the onset and cessation of exercise, it may be useful as a supplemental thermal feedback to modulate heat exchange in microclimate thermal control systems.