Hot water immersion: Maintaining core body temperature above 38.5°C mitigates muscle fatigue

PURPOSE

Hot water immersion (HWI) has gained popularity to promote muscle recovery, despite limited data on the optimal heat dose. The purpose of this study was to compare the responses of two exogenous heat strains on core body temperature, hemodynamic adjustments, and key functional markers of muscle recovery following exercise-induced muscle damage (EIMD).

METHODS

Twenty-eight physically active males completed an individually tailored EIMD protocol immediately followed by one of the following recovery interventions: HWI (40°C, HWI40 ), HWI (41°C, HWI41 ) or warm water immersion (36°C, CON36 ). Gastrointestinal temperature (Tgi ), hemodynamic adjustments (cardiac output [CO], mean arterial pressure [MAP], and systemic vascular resistance [SVR]), pre-frontal cortex deoxyhemoglobin (HHb), ECG-derived respiratory frequency, and subjective perceptual measures were tracked throughout immersion. In addition, functional markers of muscle fatigue (maximal concentric peak torque [Tpeak ]) and muscle damage (late-phase rate of force development [RFD100-200 ]) were measured prior to EIMD (pre-), 24 h (post-24 h), and 48 h (post-48 h) post-EIMD.

RESULTS

By the end of immersion, HWI41 led to significantly higher Tgi values than HWI40 (38.8 ± 0.1 vs. 38.0°C ± 0.6°C, p < 0.001). While MAP was well maintained throughout immersion, only HWI41 led to increased (HHb) (+4.2 ± 1.47 μM; p = 0.005) and respiratory frequency (+4.0 ± 1.21 breath.min-1 ; p = 0.032). Only HWI41 mitigated the decline in RFD100-200 at post-24 h (-7.1 ± 31.8%; p = 0.63) and Tpeak at post-48 h (-3.1 ± 4.3%, p = 1).

CONCLUSION

In physically active males, maintaining a core body temperature of ~25 min within the range of 38.5°C-39°C has been found to be effective in improving muscle recovery, while minimizing the risk of excessive physiological heat strain.

Physical Activity and Bone Vascularization: A Way to Explore in Bone Repair Context?

Physical activity is widely recognized as a biotherapy by WHO in the fight and prevention of bone diseases such as osteoporosis. It reduces the risk of disabling fractures associated with many comorbidities, and whose repair is a major public health and economic issue. Bone tissue is a dynamic supportive tissue that reshapes itself according to the mechanical stresses to which it is exposed. Physical exercise is recognized as a key factor for bone health. However, the effects of exercise on bone quality depend on exercise protocols, duration, intensity, and frequency. Today, the effects of different exercise modalities on capillary bone vascularization, bone blood flow, and bone angiogenesis remain poorly understood and unclear. As vascularization is an integral part of bone repair process, the analysis of the preventive and/or curative effects of physical exercise is currently very undeveloped. Angiogenesis–osteogenesis coupling may constitute a new way for understanding the role of physical activity, especially in fracturing or in the integration of bone biomaterials. Thus, this review aimed to clarify the link between physical activities, vascularization, and bone repair.

Effects of Prior Exercise on Force-Velocity Test Performance and Quadriceps EMG

This study investigated the effects of prior exercise on performance during a subsequent force-velocity (FV) exercise test. After determination of the individual maximal aerobic power (MAP) during maximal graded exercise testing, fifteen trained male subjects (age: 25 +/- 3 y) were randomly assigned to perform the FV exercise test without prior exercise (NPE) or preceded by prior exercise (PE) (10 min at 60 % of MAP, followed after 1-min rest interval by four intervals of 30-s cycling at 100 % MAP with 15-s rest intervals, then 10 min recovery). Blood samples were drawn at rest, and then for each work load at the 3rd minute of recovery. Skin temperature (T (sk)) from the rectus femoris and heart rate (HR) were measured continuously during prior exercise, the FV test, and during the 5-min recovery period at the end of each FV test. The Root Mean Square (RMS) of the surface electromyogram (EMG) signals obtained from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) were calculated during each sprint for each FV test. The lactate increase for each load (deltaLa) during the FV test was significantly less following PE than NPE. However, the lactate concentration (La) was significantly higher in the FV test following PE than NPE. There was an improvement in power output during the first two sprints (2 and 4 kg) following PE compared to NPE. There was also a more pronounced decrease in VL, VM, and RF RMS in PE compared to NPE. Our results showed that the first few sprints may provide sufficient prior exercise for the FV test. The higher lactate concentration following PE than NPE, despite no difference in maximum power, suggests that a large lactate accumulation may not be detrimental to FV test performance. However, a greater lactate concentration and T(sk) may be associated with a decrease in RMS.

Cardiorespiratory requirements and reproducibility of the six-minute walk test in elderly patients with coronary artery disease

OBJECTIVES

To measure the cardiorespiratory requirements of the six-minute walk test (6MWT), to compare this demand with the symptom-limited exercise test (SLET) at ventilatory threshold and at maximal level in elderly patients with coronary artery disease (CAD), and to assess the reproducibility of the 6MWT in cardiorespiratory exchanges in those patients.

DESIGN

Comparative and reproducibility sample.

SETTING

Cardiac rehabilitation service.

PARTICIPANTS

Twenty-five people with CAD.

INTERVENTIONS

Subjects performed an SLET and a 6MWT. To test 6MWT reproducibility, 9 patients performed 2 repeated 6MWTs.

MAIN OUTCOME MEASURES

The 6MWT cardiorespiratory values, measured with a portable gas analyzer, were compared with the SLET data and with the data from the 2 repeated 6MWTs.

RESULTS

The 6MWT peak oxygen uptake (VO2peak, 14.27+/-2.94 mL.min(-1).kg(-1)) and heart rate (94+/-14 beats/min) did not differ from the SLET values at ventilatory threshold (VO2, 13.4+/-2.65 mL.min(-1).kg(-1); heart rate, 91+/-17 beats/min), whereas the 6MWT ventilation (VEpeak, 36.72+/-10.03 L/min) was higher than the SLET at ventilatory threshold (Ve, 31.54+/-8.93 L/min, P<.03). Maximal 6MWT cardiorespiratory data were lower than the SLET maximal values. Cardiorespiratory values did not differ between the 2 repeated 6MWT (VO2peak, 15.33+/-3.52 mL.min(-1).kg(-1) vs 15.11+/-2.65 mL.min(-1).kg(-1); VEpeak, 39.07+/-12.33 L/min vs 39.07+/-12.13 L/min; heart rate, 95+/-21 beats/min vs 89+/-15 beats/min).

CONCLUSIONS

The 6MWT cardiorespiratory requirement values did not differ from SLET values at ventilatory threshold except for ventilation, and 6MWT values are reproducible in elderly patients with CAD.

Cardiorespiratory fitness and functional capacity assessed by the 20-meter shuttle walking test in patients with coronary artery disease

OBJECTIVE

To validate the 20-meter shuttle walking test (20MST) in the assessment of maximal oxygen consumption (VO(2)max) and maximal speed in patients with coronary artery disease (CAD).

DESIGN

Single-sample validity study.

SETTING

Cardiac rehabilitation service in France.

PARTICIPANTS

Seventeen men with CAD.

INTERVENTIONS

Subjects underwent a symptom-limited treadmill test (SLTT) in a laboratory, with a speed starting at 2.5km/h and increasing by 0.5km/h every minute, and performed an adapted 20MST in a corridor, with a speed starting at 3km/h and increasing by 1km/h every minute until exhaustion.

MAIN OUTCOME MEASURES

VO(2) measured during the 20MST with the Cosmed K2 telemetric gas analyzer (K2 VO(2)), estimated VO(2) calculated by the Léger equation (Léger VO(2)) from the maximal speed obtained during the 20MST, and VO(2) measured during the SLTT (SLTT VO(2)). Maximal speeds attained on the treadmill and on the 20MST were also compared.

RESULTS

A significant (P<.0001) difference was observed between the Léger estimate of VO(2) and those of K2 VO(2) and SLTT VO(2) (mean +/- standard deviation, 12.28+/-5.90mL. min(-1).kg(-1) vs 23.04+/-7.17 and 22.56+/-6.29mL.min(-1).kg(-1)). No difference was found between the treadmill and the 20MST maximal speeds (6.73+/-0.91km/h, 6.78+/-1.23km/h, respectively). Measured with the Cosmed K2, a significant relationship existed between VO(2) and each speed level (r=.95, P<.0001; VO(2)=4.24x speed-7.37, standard estimation error=2.29mL.min(-1).kg(-1)).

CONCLUSION

Maximal VO(2) and maximal speed measured on the treadmill did not differ significantly from those obtained on the 20MST. The current 20MST equation (Léger equation) was not valid to estimate VO(2) in CAD patients. A modified prediction equation of VO(2) was given and would need a larger number of patients to be generalized.

Comparison of two training programmes in chronic airway limitation patients: standardized versus individualized protocols

This study tested the effect of two methods of training, one individualized at the heart rate corresponding to the gas exchange threshold (GET) and the other at the heart rate corresponding to 50% of maximal heart rate reserve, on maximal and submaximal cardiorespiratory response in 24 patients with chronic airway limitation (CAL). The patients were randomly assigned to either the individualized training group (IT; n = 12) or the standardized training group (ST; n = 12). The training programme consisted of 4 weeks of stationary bicycle exercise, 5 days.week-1. Before reconditioning began, the target level based on heart rate was not significantly different between groups (109 +/- 4 versus 110 +/- 3 beats.min-1, in IT and ST, respectively). Post-training, a significant increase in symptom-limited oxygen uptake (V'O2.sl) and maximal O2 pulse was found in IT, whereas ST exhibited no significant change. In each group, GET was statistically increased in much the same way as V'O2,sl, with a higher increase in IT (p < 0.01) than ST (p < 0.05). Nevertheless, IT exhibited a concomitant and gradual decrease in minute ventilation (V'E), carbon dioxide production (V'CO2), and venous lactate concentration ([La]), whereas ST presented no significant change in these parameters (intergroup p < 0.01). Breathing pattern was also altered after IT, at the same metabolic level and at the same ventilation level (intergroup p < 0.05). Cardiac responses were modified in the two groups. At the same metabolic level, a significantly lower cardiac frequency was found both for IT and ST (intragroup p < 0.05 after training). In contrast, the increase in O2 pulse was only significantly higher in It after training. These data show the greater efficiency of an individualized training protocol based on determination of gas exchange threshold as compared to a standardized protocol, in improving exercise performance, when applied to a patient group. Despite an apparently similar target training level, the individualized method clearly optimized the physiological training effects in patients with chronic airway limitation and, more particularly, decreased their ventilatory requirement.

Caffeine increases maximal anaerobic power and blood lactate concentration

The aim of this study was to specify the effects of caffeine on maximal anaerobic power (Wmax). A group of 14 subjects ingested caffeine (250 mg) or placebo in random double-blind order. The Wmax was determined using a force-velocity exercise test. In addition, we measured blood lactate concentration for each load at the end of pedalling and after 5 min of recovery. We observed that caffeine increased Wmax [964 (SEM 65.77) W with caffeine vs 903.7 (SEM 52.62) W with placebo; P less than 0.02] and blood lactate concentration both at the end of pedalling [8.36 (SEM 0.95) mmol.l-1 with caffeine vs 7.17 (SEM 0.53) mmol.l-1 with placebo; P less than 0.01] and after 5 min of recovery [10.23 (SEM 0.97) mmol.l-1 with caffeine vs 8.35 (SEM 0.66) mmol.l-1 with placebo; P less than 0.04]. The quotient lactate concentration/power (mmol.l-1.W-1) also increased with caffeine at the end of pedalling [7.6.10(-3) (SEM 3.82.10(-5)) vs 6.85.10(-3) (SEM 3.01.10(-5)); P less than 0.01] and after 5 min of recovery [9.82.10(-3) (SEM 4.28.10(-5)) vs 8.84.10(-3) (SEM 3.58.10(-5)); P less than 0.02]. We concluded that caffeine increased both Wmax and blood lactate concentration.