The Influence of Different External Cooling Methods on Thermoregulatory Responses Before and After Intense Intermittent Exercise in the Heat

It is well known that hyperosmolality suppresses thermoregulatory responses and that plasma osmolality (Posmol) increases with exercise intensity. We examined whether the decreased esophageal temperature thresholds for cutaneous vasodilation (THFVC) and sweating (THSR) after 10-day endurance training (ET) are caused by either attenuated increase in Posmol at a given exercise intensity or blunted sensitivity of hyperosmotic suppression. Nine young male volunteers exercised on a cycle ergometer at 60% peak oxygen consumption rate (V̇o2 peak) for 1 h/day for 10 days at 30°C. Before and after ET, thermoregulatory responses were measured during 20-min exercise at pretraining 70% V̇o2 peak in the same environment as during ET under isoosmotic or hyperosmotic conditions. Hyperosmolality by ∼10 mosmol/kgH2O was attained by acute hypertonic saline infusion. After ET, V̇o2 peak and blood volume (BV) both increased by ∼4% ( P < 0.05), followed by a decrease in THFVC ( P < 0.05) but not by that in THSR. Although there was no significant decrease in Posmol at the thresholds after ET, the sensitivity of increase in THFVC at a given increase in Posmol [ΔTHFVC/ΔPosmol,°C·(mosmol/kgH2O)−1], determined by hypertonic infusion, was reduced to 0.021 ± 0.005 from 0.039 ± 0.004 before ET ( P < 0.05). The individual reductions in ΔTHFVC/ΔPosmol after ET were highly correlated with their increases in BV around THFVC ( r = −0.89, P < 0.005). In contrast, there was no alteration in the sensitivity of the hyperosmotic suppression of sweating after ET. Thus the downward shift of THFVC after ET was partially explained by the blunted sensitivity to hyperosmolality, which occurred in proportion to the increase in BV.

Download Full-text

Reversal of muscle fatigue during 16 h of heavy intermittent cycle exercise

Journal of Applied Physiology ◽

10.1152/japplphysiol.00565.2004 ◽

2004 ◽

Vol 97 (6) ◽

pp. 2166-2175 ◽

Cited By ~ 11

Author(s):

H. J. Green ◽

T. A. Duhamel ◽

S. Ferth ◽

G. P. Holloway ◽

M. M. Thomas ◽

...

Keyword(s):

Oxygen Consumption ◽

Muscle Fatigue ◽

Intermittent Exercise ◽

Low Frequency ◽

Quadriceps Muscle ◽

Stimulation Frequency ◽

Peak Oxygen Consumption ◽

Force Frequency ◽

Reduction In Force ◽

Before And After

This study examined the effects of extended sessions of heavy intermittent exercise on quadriceps muscle fatigue and weakness. Twelve untrained volunteers (10 men and 2 women), with a peak oxygen consumption of 44.3 ± 2.3 ml·kg−1·min−1, exercised at ∼91% peak oxygen consumption for 6 min once per hour for 16 h. Muscle isometric properties assessed before and after selected repetitions (R1, R2, R4, R7, R12, and R15) were used to quantitate fatigue (before vs. after repetitions) and weakness (before vs. before repetitions). Muscle fatigue at R1 was indicated by reductions ( P < 0.05) in peak twitch force (135 ± 13 vs. 106 ± 11 N) and by a reduction ( P < 0.05) in the force-frequency response, which ranged between ∼53% at 10 Hz (113 ± 12 vs. 52.6 ± 7.4 N) and ∼17% at 50 Hz (324 ± 27 vs. 270 ± 30 N). No recovery of force, regardless of stimulation frequency, was observed during the 54 min between R1 and R2. At R2 and for all subsequent repetitions, no reduction in force, regardless of stimulation frequency, was generally found after the exercise. The only exception was for R2, where, at 20 Hz, force was reduced ( P < 0.05) by 18%. At R15, force before repetitions for high frequencies (i.e., 100 Hz) returned to R1 (333 ± 29 vs. 324 ± 27 N), whereas force at low frequency (i.e., 10 Hz) was only partially ( P < 0.05) recovered (113 ± 12 vs. 70 ± 6.6 N). It is concluded that multiple sessions of heavy exercise can reverse the fatigue noted early and reduce or eliminate weakness depending on the frequency of stimulation.

Download Full-text

Agonist of TRPM8 channel, menthol, facilitates the initiation of thermoregulatory responses to external cooling

Journal of Thermal Biology ◽

10.1016/j.jtherbio.2010.09.004 ◽

2010 ◽

Vol 35 (8) ◽

pp. 428-434 ◽

Cited By ~ 15

Author(s):

T.V. Kozyreva ◽

V.P. Kozaruk ◽

E.Ya. Tkachenko ◽

G.M. Khramova

Keyword(s):

Trpm8 Channel ◽

Thermoregulatory Responses ◽

External Cooling

Download Full-text

Sprint training increases human skeletal muscle Na(+)-K(+)-ATPase concentration and improves K+ regulation

Journal of Applied Physiology ◽

10.1152/jappl.1993.75.1.173 ◽

1993 ◽

Vol 75 (1) ◽

pp. 173-180 ◽

Cited By ~ 134

Author(s):

M. J. McKenna ◽

T. A. Schmidt ◽

M. Hargreaves ◽

L. Cameron ◽

S. L. Skinner ◽

...

Keyword(s):

Skeletal Muscle ◽

Binding Site ◽

Intermittent Exercise ◽

Recovery Period ◽

Muscle Performance ◽

Vastus Lateralis Muscle ◽

Work Output ◽

Sprint Training ◽

Ouabain Binding ◽

Before And After

This study investigated the effects of sprint training on muscle Na(+)-K(+)-adenosinetriphosphatase (ATPase) concentration, plasma [K+] regulation, muscle performance, and fatigue during severe intermittent exercise. Six untrained male subjects underwent intensive cycle-sprint training for 7 wk. Muscle biopsies were taken at rest from the vastus lateralis muscle before and after 7 wk of training and were assayed for Na(+)-K(+)-ATPase concentration using vanadate-facilitated [3H]ouabain binding to intact samples. Before and after the training period, subjects performed four maximal 30-s exercise bouts (EB) on a cycle ergometer, each separated by a 4-min recovery. Arterialized venous blood samples were drawn immediately before and after each sprint bout and were analyzed for plasma [K+]. The work output was significantly elevated (11%) across all four EBs after training. The muscle [3H]ouabain binding site concentration was significantly increased (16%) from 333 +/- 19 to 387 +/- 15 (SE) pmol/g wet wt after training but was unchanged in muscle obtained from three control subjects. Plasma [K+] rose by 1–2 mmol/l with each EB and declined rapidly by the end of each recovery period. The increases in plasma [K+] resulting from each EB were significantly lower (19%) after training. The ratios of rise in plasma [K+] relative to work output during each EB were also significantly lower (27%) after training. The increased muscle [3H]ouabain binding site concentration and the reduced ratio of rise in [K+] relative to work output with exercise are both consistent with improved plasma and skeletal muscle K+ regulation after sprint training.

Download Full-text

The Influence of Intermittent Fatigue Exercise on Early and Late Phases of Relaxation From Maximal Voluntary Contraction

Canadian Journal of Applied Physiology ◽

10.1139/h97-037 ◽

1997 ◽

Vol 22 (6) ◽

pp. 573-584 ◽

Cited By ~ 6

Author(s):

Anna Jaskólska ◽

Artur Jaskólski

Keyword(s):

Relaxation Time ◽

Relaxation Rate ◽

Maximal Voluntary Contraction ◽

Early Phase ◽

Intermittent Exercise ◽

Young Male ◽

Voluntary Contraction ◽

Hand Grip ◽

Before And After ◽

Late Relaxation Time

Twenty-two young male subjects were tested to estimate the behavior of the early and late phases of relaxation from a 3-s maximal voluntary contraction (MVC) under the influence of fatigue. Less demanding and more demanding protocols of intermittent hand grip exercise were used to fatigue muscle. Before and after fatigue, the early and late relaxation time, maximal relaxation rate, and half-relaxation time were measured. The results showed that during voluntary movement (a) the early phase of relaxation was independent of the mode of intermittent exercise and did not change significantly after fatigue; (b) the late relaxation time and absolute maximal relaxation rate were slower after both protocols, with the changes more pronounced following the more demanding protocol; and (c) the half-relaxation time and relative maximal relaxation rate were changed only in the more demanding protocol. It is concluded that unlike the relaxation following electrical stimulation of isolated muscle, the early phase of relaxation from voluntary contraction appears to be the most resistant to the type of intermittent fatiguing exercise used in the present study, whereas the late relaxation time was the most sensitive to this type of fatigue. Key words: hand grip exercise, late relaxation time, early relaxation time, half-relaxation time

Download Full-text

Caffeine counteracts the ergogenic action of muscle creatine loading

Journal of Applied Physiology ◽

10.1152/jappl.1996.80.2.452 ◽

1996 ◽

Vol 80 (2) ◽

pp. 452-457 ◽

Cited By ~ 110

Author(s):

K. Vandenberghe ◽

N. Gillis ◽

M. Van Leemputte ◽

P. Van Hecke ◽

F. Vanstapel ◽

...

Keyword(s):

Intermittent Exercise ◽

Creatine Supplementation ◽

Knee Extensors ◽

Caffeine Intake ◽

Resonance Spectroscopy ◽

Experimental Conditions ◽

Before And After ◽

And Performance ◽

Exercise Fatigue ◽

Voluntary Contractions

This study aimed to compare the effects of oral creatine (Cr) supplementation with creatine supplementation in combination with caffeine (Cr+C) on muscle phosphocreatine (PCr) level and performance in healthy male volunteers (n = 9). Before and after 6 days of placebo, Cr (0.5 g x kg-1 x day-1), or Cr (0.5 g x kg-1 x day-1) + C (5 mg x kg-1 x day-1) supplementation, 31P-nuclear magnetic resonance spectroscopy of the gastrocnemius muscle and a maximal intermittent exercise fatigue test of the knee extensors on an isokinetic dynamometer were performed. The exercise consisted of three consecutive maximal isometric contractions and three interval series of 90, 80, and 50 maximal voluntary contractions performed with a rest interval of 2 min between the series. Muscle ATP concentration remained constant over the three experimental conditions. Cr and Cr+C increased (P < 0.05) muscle PCr concentration by 4-6%. Dynamic torque production, however, was increased by 10-23% (P < 0.05) by Cr but was not changed by Cr+C. Torque improvement during Cr was most prominent immediately after the 2-min rest between the exercise bouts. The data show that Cr supplementation elevates muscle PCr concentration and markedly improves performance during intense intermittent exercise. This ergogenic effect, however, is completely eliminated by caffeine intake.

Download Full-text