Effects of temperature on the maximal instantaneous muscle power of humans

Energetic responses of head-out water immersion at different temperatures during post-exercise recovery and its consequence on anaerobic mechanical power

PURPOSE

While exercise recovery may be beneficial from a physiological point of view, it may be detrimental to subsequent anaerobic performance. To investigate the energetic responses of water immersion at different temperatures during post-exercise recovery and its consequences on subsequent anaerobic performance, a randomized and controlled crossover experimental design was performed with 21 trained cyclists.

METHOD

Participants were assigned to receive three passive recovery strategies during 10 min after a Wingate Anaerobic Test (WAnT): control (CON: non-immersed condition), cold water immersion (CWI: 20 ℃), and hot water immersion (HWI: 40 ℃). Blood lactate, cardiorespiratory, and mechanical outcomes were measured during the WAnT and its recovery. Time constant (τ), asymptotic value, and area under the curve (AUC) were quantified for each physiologic parameter during recovery. After that, a second WAnT test and 10-min recovery were realized in the same session.

RESULTS

Regardless the water immersion temperature, water immersion increased [Formula: see text] (+ 18%), asymptote ([Formula: see text]+ 16%, [Formula: see text] + 13%, [Formula: see text] + 17%, HR + 16%) and AUC ([Formula: see text]+ 27%, [Formula: see text] + 18%, [Formula: see text] + 20%, HR + 25%), while decreased [Formula: see text] (- 33%). There was no influence of water immersion on blood lactate parameters. HWI improved the mean power output during the second WAnT (2.2%), while the CWI decreased 2.4% (P < 0.01).

CONCLUSION

Independent of temperature, water immersion enhanced aerobic energy recovery without modifying blood lactate recovery. However, subsequent anaerobic performance was increased only during HWI and decreased during CWI. Despite higher than in other studies, 20 °C effectively triggered physiological and performance responses. Water immersion-induced physiological changes did not predict subsequent anaerobic performance.

More than energy cost: multiple benefits of the long Achilles tendon in human walking and running

Elastic strain energy that is stored and released from long, distal tendons such as the Achilles during locomotion allows for muscle power amplification as well as for reduction of the locomotor energy cost: as distal tendons perform mechanical work during recoil, plantar flexor muscle fibres can work over smaller length ranges, at slower shortening speeds, and at lower activation levels. Scant evidence exists that long distal tendons evolved in humans (or were retained from our more distant Hominoidea ancestors) primarily to allow high muscle-tendon power outputs, and indeed we remain relatively powerless compared to many other species. Instead, the majority of evidence suggests that such tendons evolved to reduce total locomotor energy cost. However, numerous additional, often unrecognised, advantages of long tendons may speculatively be of greater evolutionary advantage, including the reduced limb inertia afforded by shorter and lighter muscles (reducing proximal muscle force requirement), reduced energy dissipation during the foot-ground collisions, capacity to store and reuse the muscle work done to dampen the vibrations triggered by foot-ground collisions, reduced muscle heat production (and thus core temperature), and attenuation of work-induced muscle damage. Cumulatively, these effects should reduce both neuromotor fatigue and sense of locomotor effort, allowing humans to choose to move at faster speeds for longer. As these benefits are greater at faster locomotor speeds, they are consistent with the hypothesis that running gaits used by our ancestors may have exerted substantial evolutionary pressure on Achilles tendon length. The long Achilles tendon may therefore be a singular adaptation that provided numerous physiological, biomechanical, and psychological benefits and thus influenced behaviour across multiple tasks, both including and additional to locomotion. While energy cost may be a variable of interest in locomotor studies, future research should consider the broader range of factors influencing our movement capacity, including our decision to move over given distances at specific speeds, in order to understand more fully the effects of Achilles tendon function as well as changes in this function in response to physical activity, inactivity, disuse and disease, on movement performance.

Passive Heating Increases Bench-Pull Power Output in Highly Trained Swimmers

PURPOSE

Determine the effects of skin temperature change on bench-pull power following a passive warm-up intervention with highly trained swimmers using multiple heated clothing garments.

METHODS

Using a crossover design, 8 high-performance swimmers (mean [SD]; age, 22.4 [4.4] y; body mass, 74.9 [8.1] kg; height, 1.79 [0.09] m; world record ratio, 107.3% [5.1%]) completed a pool-based warm-up followed by a 35-minute transition phase before completing 3 repetitions at 50% of 1-repetition maximum of the bench-pull exercise. During transition, swimmers wore either a warm (control) or a heated (heat) clothing condition.

RESULTS

Following heating, mean skin temperature was 0.7 °C higher in heat (P = .011), though no change was seen in tympanic temperature. Bench-pull mean and peak power improved by 4.5% and 4.7% following heating, respectively. A large repeated-measures correlation was observed between skin temperature and mean (r [90% CI] = .94 [.65 to .99], P < .01) and peak (r [90% CI] = .89 [.45 to .98], P < .01) power output. Thermal sensation and comfort at all regions were higher with heating (P ≤ .02).

CONCLUSION

Combined upper- and lower-limb passive heating can increase whole-body skin temperature and improve short-duration upper-limb power output during the bench-pull exercise. Improvements in power output were directly related to the skin temperature increase facilitated by the heated clothing.

The effect of cold-water immersion on physical performance

Cold modalities are widely used after athletic injuries, with known physiological effects. The aim of this study was to determine the effects of cold-water immersion on physical performance. Thirty healthy volunteers (average age of 19-23 years) took part in this pre-post interventional study. First, participants performed two tasks: a 40-yard dash run (to measure speed) and a vertical jump (to measure lower limb power). Then, both legs were immersed in a water bath at 5 °C for 15 min. Following cold-water immersion, the measurements were repeated after 2, 5, 10, 15, 20, 25 and 30 min. Immediately (2 min) after cold-water immersion, there was a decline in both the vertical jump and 40-yard dash tests compared to pre-intervention scores. While this effect lasted up to 20 min after cryotherapy for the 40-yard dash test, for the jump test, the effect only remained up to 10 min. The results showed a decrease in physical performance immediately and 20 min after immersion in cold water (p < 0.05). In addition, there was a gradual increase in the level of physical function over time. Therefore, before returning athletes to activity after the use of cold modalities, care should be taken.

Experimental validation of the 3-parameter critical power model in cycling

PURPOSE

The three-parameter model of critical power (3-p) implies that in the severe exercise intensity domain time to exhaustion (T_lim) decreases hyperbolically with power output starting from the power asymptote (critical power, ẇ_cr) and reaching 0 s at a finite power limit (ẇ₀) thanks to a negative time asymptote (k). We aimed to validate 3-p for short T_lim and to test the hypothesis that ẇ₀ represents the maximal instantaneous muscular power.

METHODS

Ten subjects performed an incremental test and nine constant-power trials to exhaustion on an electronically braked cycle ergometer. All trials were fitted to 3-p by means of non-linear regression, and those with T_lim greater than 2 min also to the 2-parameter model (2-p), obtained constraining k to 0 s. Five vertical squat jumps on a force platform were also performed to determine the single-leg (i.e., halved) maximal instantaneous power.

RESULTS

T_lim ranged from 26 ± 4 s to 15.7 ± 4.9 min. In 3-p, with respect to 2-p, ẇ_cr was identical (177 ± 26 W), while curvature constant W' was higher (17.0 ± 4.3 vs 15.9 ± 4.2 kJ, p < 0.01). 3-p-derived ẇ₀ was lower than single-leg maximal instantaneous power (1184 ± 265 vs 1554 ± 235 W, p < 0.01).

CONCLUSIONS

3-p is a good descriptor of the work capacity above ẇ_cr up to T_lim as short as 20 s. However, since there is a discrepancy between estimated ẇ₀ and measured maximal instantaneous power, a modification of the model has been proposed.

Restoration of thermoregulation after exercise

Performing exercise, especially in hot conditions, can heat the body, causing significant increases in internal body temperature. To offset this increase, powerful and highly developed autonomic thermoregulatory responses (i.e., skin blood flow and sweating) are activated to enhance whole body heat loss; a response mediated by temperature-sensitive receptors in both the skin and the internal core regions of the body. Independent of thermal control of heat loss, nonthermal factors can have profound consequences on the body's ability to dissipate heat during exercise. These include the activation of the body's sensory receptors (i.e., baroreceptors, metaboreceptors, mechanoreceptors, etc.) as well as phenotypic factors such as age, sex, acclimation, fitness, and chronic diseases (e.g., diabetes). The influence of these factors extends into recovery such that marked impairments in thermoregulatory function occur, leading to prolonged and sustained elevations in body core temperature. Irrespective of the level of hyperthermia, there is a time-dependent suppression of the body's physiological ability to dissipate heat. This delay in the restoration of postexercise thermoregulation has been associated with disturbances in cardiovascular function which manifest most commonly as postexercise hypotension. This review examines the current knowledge regarding the restoration of thermoregulation postexercise. In addition, the factors that are thought to accelerate or delay the return of body core temperature to resting levels are highlighted with a particular emphasis on strategies to manage heat stress in athletic and/or occupational settings.

Cold Stress Effects on Exposure Tolerance and Exercise Performance

Cold weather can have deleterious effects on health, tolerance, and performance. This paper will review the physiological responses and external factors that impact cold tolerance and physical performance. Tolerance is defined as the ability to withstand cold stress with minimal changes in physiological strain. Physiological and pathophysiological responses to short-term (cold shock) and long-term cold water and air exposure are presented. Factors (habituation, anthropometry, sex, race, and fitness) that influence cold tolerance are also reviewed. The impact of cold exposure on physical performance, especially aerobic performance, has not been thoroughly studied. The few studies that have been done suggest that aerobic performance is degraded in cold environments. Potential physiological mechanisms (decreases in deep body and muscle temperature, cardiovascular, and metabolism) are discussed. Likewise, strength and power are also degraded during cold exposure, primarily through a decline in muscle temperature. The review also discusses the concept of thermoregulatory fatigue, a reduction in the thermal effector responses of shivering and vasoconstriction, as a result of multistressor factors, including exhaustive exercise.

Effect of run training and cold-water immersion on subsequent cycle training quality in high-performance triathletes

The purpose of the study was to investigate the effect of cold-water immersion (CWI) on physiological, psychological, and biochemical markers of recovery and subsequent cycling performance after intensive run training. Seven high-performance male triathletes (age: 28.6 ± 7.1 years; cycling VO2peak: 73.4 ± 10.2 ml · kg(-1) · min(-1)) completed 2 trials in a randomized crossover design consisting of 7 × 5-minute running intervals at 105% of individual anaerobic threshold followed by either CWI (10 ± 0.5° C) or thermoneutral water immersion (TNI; 34 ± 0.5° C). Subjects immersed their legs in water 5 times for 60 seconds with 60-second passive rest between each immersion. Nine hours after immersion, inflammatory and muscle damage markers, and perceived recovery measures were obtained before the subjects completed a 5-minute maximal cycling test followed by a high-quality cycling interval training set (6 × 5-minute intervals). Power output, heart rate, blood lactate (La), and rating of perceived exertion (RPE) were also recorded during the cycling time-trial and interval set. Performance was enhanced (change, ± 90% confidence limits) in the CWI condition during the cycling interval training set (power output [W · kg(-1)], 2.1 ± 1.7%, La [mmol · L(-1)], 18 ± 18.1%, La:RPE, 19.8 ± 17.5%). However, there was an unclear effect of CWI on 5-minute maximal cycling time-trial performance, and there was no significant influence on perceptual measures of fatigue/recovery, despite small to moderate effects. The effect of CWI on the biochemical markers was mostly unclear, however, there was a substantial effect for interleukin-10 (20 ± 13.4%). These results suggest that compared with TNI, CWI may be effective for enhancing cycling interval training performance after intensive interval-running training.

Precooling leg muscle improves intermittent sprint exercise performance in hot, humid conditions

We used three techniques of precooling to test the hypothesis that heat strain would be alleviated, muscle temperature (Tmu) would be reduced, and as a result there would be delayed decrements in peak power output (PPO) during exercise in hot, humid conditions. Twelve male team-sport players completed four cycling intermittent sprint protocols (CISP). Each CISP consisted of twenty 2-min periods, each including 10 s of passive rest, 5 s of maximal sprint against a resistance of 7.5% body mass, and 105 s of active recovery. The CISP, preceded by 20 min of no cooling (Control), precooling via an ice vest (Vest), cold water immersion (Water), and ice packs covering the upper legs (Packs), was performed in hot, humid conditions (mean +/- SE; 33.7 +/- 0.3 degrees C, 51.6 +/- 2.2% relative humidity) in a randomized order. The rate of heat strain increase during the CISP was faster in Control than Water and Packs (P < 0.01), but it was similar to Vest. Packs and Water blunted the rise of Tmu until minute 16 and for the duration of the CISP (40 min), respectively (P < 0.01). Reductions in PPO occurred from minute 32 onward in Control, and an increase in PPO by approximately 4% due to Packs was observed (main effect; P < 0.05). The method of precooling determined the extent to which heat strain was reduced during intermittent sprint cycling, with leg precooling offering the greater ergogenic effect on PPO than either upper body or whole body cooling.

Lower Leg Cold Immersion Does Not Impair Dynamic Stability in Healthy Women

Context:

Previous studies have suggested that cryotherapy affects neuromuscu-lar function and therefore might impair dynamic stability. If cryotherapy affects dynamic stability, clinicians might alter their decisions regarding returning athletes to play immediately after treatment.

Objective:

To assess the effects of lower leg cold immersion on muscle activity and dynamic stability of the lower extremity.

Design:

Within-subject time-series design with 1 pretest and 2 posttests.

Setting:

A climate-controlled biomechanics laboratory.

Participants:

17 healthy women.

Interventions:

20-minute cold-water immersion.

Main Outcome Measures:

Preparatory and reactive electromyographic activity of the tibialis anterior and peroneus longus and time to stabilization after a jump landing.

Results:

Preparatory activity of the tibialis anterior increased after treatment, whereas preparatory and reactive peroneus longus activity decreased. Both returned to baseline after a 5-minute recovery. Time to stabilization did not change.

Conclusions:

Lower leg cold-immersion therapy does not impair dynamic stability in healthy women during a jump-landing task. Return to participation after a cryotherapy treatment is not contraindicated for healthy athletes.

Local tissue temperature effects on peak torque and muscular endurance during isometric knee extension

The aim of the study was to investigate the relationship between local tissue temperature, peak torque and time to fatigue during isometric knee extensions. Nine males performed maximum voluntary contractions (MVCs) and isometric knee extensions at 70% MVC to exhaustion after 30 min of hot [H, 47.7 (1.3) degrees C; mean (SD)], warm [W, 34.6 (0.4) degrees C], temperate [T, 24.5 (1.3) degrees C], and cold [C, -11.9 (1.8) degrees C] localized temperature applications. Isometric peak torque was not significantly affected by temperature. Time to fatigue was strongly and negatively correlated ( r=-0.98) to temperature, with endurance after H [46.99 (4.98) s] and W [54.36 (9.18) s] significantly shorter than after C [73.27 (13.43) s]. We conclude that local tissue temperature does not impair peak force production but may change muscular endurance through local factors.

Local temperature changes and human skeletal muscle metabolism

The aim of this review is to describe the effects induced by local temperature changes on human skeletal muscle metabolism. More specifically, we will consider the influence of temperature on the mechanical properties of muscle contraction, on aerobic metabolism, anaerobic metabolism and on the Lohmann reaction. The text has been voluntarily organized on the basis of a simple bioenergetic model describing the different energy fluxes appearing in the muscle system. This approach should better highlight some of the points that still need to be investigated. Although it was not always possible to restrict the discussion to human muscle, the references report mainly data obtained directly on humans or on isolated human fibres. A short comment on skeletal muscle temperature measurement techniques, on humans, is also included.

Maximal instantaneous muscular power after prolonged bed rest in humans

A reduction in lower limb cross-sectional area (CSA) occurs after bed rest (BR). This should lead to an equivalent reduction in maximal instantaneous muscular power (W(p)) if the body segments' lengths remain unchanged. W(p) was determined during maximal jumps off both feet on a force platform before and on days 2, 6, 10, 32, and 48 after a 42-day duration BR. CSA of thigh muscles was measured by magnetic resonance imaging before and on day 5 after BR. Before BR, W(p) was 3.63 +/- 0.43 kW or 48.6 +/- 3.3 W/kg. On days 2 and 6 after BR, W(p) was reduced by 23.7 +/- 6.9 and 22.7 +/- 5.4% (P < 0.01), respectively. Thigh extensors CSA (CSAEXT) was 16.7 +/- 4.7% (P < 0.01) lower than before. When normalized per CSAEXT, W(p) was reduced by only 4.8 +/- 4.5% (P < 0.05). By day 48 of recovery, W(p) had returned to baseline values. Therefore, if W(p) is appropriately normalized for CSA of the extensor muscles, the reduction in CSAEXT explains most of the decrease in W(p) decrease after BR. Other factors such as a deficit in neural activation or a decrease in fiber-specific tension may account for only 5% of the W(p) loss after BR.

Effects of external loading on power output in a squat jump on a force platform: a comparison between strength and power athletes and sedentary individuals

The aim of this study was to determine the effects of external loading on power output during a squat jump on a force platform in athletes specializing in strength and power events (6 elite weight-lifters and 16 volleyball players) and in 20 sedentary individuals. Instantaneous power was computed from time-force curves during vertical jumps with and without an external load (0, 5 or 10 kg worn in a special vest). The jumps were performed from a squat position, without lower limb counter-movement or an arm swing. Peak instantaneous power corresponded to the highest value of instantaneous power during jumping. Average power throughout the push phase of the jump was also calculated. A two-way analysis of variance showed significant interactions between the load and group effects for peak instantaneous power (P< 0.01) and average power (P< 0.001). Peak instantaneous power decreased significantly in sedentary individuals when moderate external loads were added. The peak instantaneous power at 0 kg was greater than that at 5 and 10 kg in the sedentary individuals. In contrast, peak instantaneous power was independent of load in the strength and power athletes. Mean power at 0 kg was significantly lower than at 5 kg in the athletes; at 0 kg it was significantly higher than at 10 kg in the sedentary males and at 5 and 10 kg in the sedentary females. In all groups, the force corresponding to peak instantaneous power increased and the velocity corresponding to peak instantaneous power decreased with external loading. The present results suggest that the effects of external loading on peak instantaneous power are not significant in strength and power athletes provided that the loads do not prevent peak velocity from being higher than the velocity that is optimal for maximal power output.

The Effects of Cryotherapy on Ground-Reaction Forces Produced during a Functional Task

Objective:

To determine whether a standard 20-min ice-bath (10°C) immersion of the leg alters vertical ground-reaction-force components during a 1 -legged vertical jump.

Design:

A 1 × 5 factorial repeated-measures model was used.

Setting:

The Applied Biomechanics Laboratory at The University of Mississippi.

Participants:

Fifteen healthy and physically active subjects (age = 22.3 ± 2.1 years, height = 177.3 ± 12.2 cm, mass = 76.3 ± 19.1 kg) participated.

Intervention:

Subjects performed 25 one-legged vertical jumps with their preferred extremity before (5 jumps) and after (20 jumps) a 20-min cold whirlpool to the leg. The 25 jumps were reduced into 5 sets of average trials.

Main Outcome Measures:

Normalized peak and average vertical ground-reaction forces, as well as vertical impulse obtained using an instrumented force platform.

Results:

Immediately after cryotherapy (sets 2 and 3), vertical impulse decreased (P= .01); peak vertical ground-reaction force increased (set 2) but then decreased toward baseline measures (P= .02). Average vertical ground-reaction force remained unchanged (P>.05).

Conclusions:

The authors advocate waiting approximately 15 min before engaging in activities that require the production of weight-bearing explosive strength or power.

Determinants of peak muscle power: effects of age and physical conditioning

The relationships between absolute peak muscle power (Wpeak), muscle cross sectional area (CSAtot, i.e. the sum of both thigh and calf CSA) and muscle high energy phosphate concentration (adenosine 5'-triphosphate [ATP] and phosphocreatine concentrations [PC]) were studied in 47 subjects classified into five groups: A, 10 sedentary (S) subjects aged 20-35 years; B, 9 S aged 35-50 years; C, 9 S aged more than 50 years; D, 13 children aged 8-13 years; and E, 6 athletes (top level volleyball players) aged 24 (SD 3) years. The Wpeak was measured during a maximal vertical high jump off both feet on a force platform. The CSAtot was measured anthropometrically. The [ATP] and [PC] were determined by 31Phosphorus nuclear magnetic resonance spectroscopy. The Wpeak decreased with age, was 65% lower in D than in A, and 43% higher in E than in A. The CSAtot did not vary with age, was 45% smaller in D than in A, and 15% greater in E than in A. The [ATP] and [PC] were essentially the same in all groups. The changes observed in Wpeak were only partially accounted for by changes in CSAtot. Therefore, in addition to the variables investigated, other factors appear to have been involved in the determination of Wpeak with increasing age and training. An important role may be played by hormonal, particularly at puberty, and neural factors.

Effects of muscle temperature on the VO2 kinetics at the onset of exercise in man

The kinetics (i.e. the rate of readjustment) of O2 uptake (VO2) at the mouth of muscle blood flow in the vastus lateralis muscle (Qm), and the net accumulation of lactate in the rest-to-exercise transient (early lactate) were assessed in 6 untrained men (age 31 +/- 8 (SD) yrs) during constant-load 5-min duration exercises on the cyclo ergometer of 75 and 125 W, performed at muscle temperatures (Tm) of 35.5 +/- 0.9 degrees C (N) and of 28.0 +/- 1.65 degrees C (C). VO2 was measured breath-by-breath; Qm was assessed from 133Xe clearance; early lactate was calculated as the difference between the venous lactate concentrations observed after and before exercise. At both work loads, steady-state VO2 was slightly higher in N than in C (P less than 0.05 at 75 W; NS at 125 W). The half-times of VO2 kinetics were: in N, 36.2 +/- 6.7 s at 75 W and 41.6 +/- 8.6 s at 125 W; in C, 41.4 +/- 10.0 at 75 W and 43.8 +/- 14.0 at 125 W (NS). Mean steady state Qm was 8.5 ml.min-1.100 g-1 in C, and 13.4 in N at 75 W (NS); at 125 W, Qm was 18.3 ml.min-1.100 g-1 in C vs. 25.0 in N (NS). The half-times of the Qm kinetics tended to be slower in C than in N (NS). At both work loads, early lactate was slightly greater in C than in N (NS). It is concluded that, at submaximal exercise, (a) steady state VO2 and the VO2 kinetics are not affected by Tm, and (b) at the onset of exercise Qm does not affect VO2 kinetics.