Heat shock protein response during fixed intensity and self-paced exercise in the heat in young, healthy women on oral contraceptives compared with young healthy men.

Background: Heat shock proteins respond to a variety of physiological and environmental stresses, including heat stress, ischemia and endotoxic shock. Hormonal changes during the female menstrual cycle can have a thermogenic effect on body temperature. The monophasic oral contraceptive (OC) pill provides low doses of progesterone and oestrogen over the course of the normal menstrual phase. There is little evidence regarding the combined effects of OC on exercise performance and heat stress with respect to heat shock protein response. Objectives: This study aimed to determine the response of heat shock proteins (Hsp72) during fixed-intensity and self-paced exercise in the heat in young, healthy women on oral contraceptives compared with young healthy men. Methods: Sixteen physically active men and women performed 30 min fixed-intensity cycling at 50% of maximum workload, followed by 30 min of a self-paced time trial (TT) interspersed by 30 s maximal sprint at 9, 19 and 29 min respectively. Trials were undertaken in cool (20°C; 48±3% relative humidity (RH)) and warm (32°C; 66±2% RH) ambient conditions. Core (T c) and skin temperature, heart rate (HR) and subjective responses were measured before, during and post exercise. Results: The distance, mean and peak power output, mean and peak speed during the self-paced time trial showed no difference between the ambient temperatures for men and women. Hsp72 in females was higher than males at all sample points at both 20°C and 32°C, except for pre-exercise at 20°C (p< 0.04). Women also attained a higher T c than men at the end of the TT in the heat (38.5°C v 37.9°C for women and men, respectively; p<0.03), higher mean HR and perceived exertion. Conclusion: This study indicates that females who use oral contraceptives (OC) had higher levels of Hsp72 than males when tested under the same environmental conditions.

Cerebral oxygenation and sympathetic responses to smoking in young and middle-aged smokers.

This study examined the effects of acute tobacco smoking on cerebral oxygenation and autonomic function in 28 male, habitual smokers of shorter young smokers (YSM) or longer middle-aged smokers (MSM) smoking history. Following baseline testing, participants undertook a smoking protocol involving the consumption of two cigarettes within 15 min. Measures of cerebral oxygenation and autonomic function were collected before, during, and 0 min, 30 min, 1 h, and 4 h post-smoking. Tissue saturation index (TSI) for MSM was greater than YSM during cigarette consumption ( p < 0.05). Moreover, MSM observed significant within-group changes for TSI during and post-cigarette consumption ( p < 0.05). Further, MSM observed an increase in low frequency (LF) band from 30 min to 1 h post-consumption, followed by a decline, whereas elevations above MSM were observed in YSM at 4 h ( p < 0.05). Both MSM and YSM showed a decrease in high-frequency (HF) band post-cigarette, while increased LF/HF ratio post-consumption was observed in YSM. A decline in the standard deviation of RR intervals, post-cigarette consumption was evident in MSM ( p < 0.05). Moreover, the root mean square of RR interval in both groups similarly decreased following cigarette consumption ( p < 0.05). Acute smoking affects heart rate variability, suggestive of vagal withdrawal, and maybe indicate an effect of smoking history. Additionally, prolonged smoking history alters cerebral microcirculatory responses to acute tobacco exposure in MSM.

Prefrontal and motor cortex EEG responses and their relationship to ventilatory thresholds during exhaustive incremental exercise.

PURPOSE: The purpose of this study was to measure the EEG response in the prefrontal cortex (PFC) and motor cortex (MC) during incremental exercise and align these responses with ventilatory parameters. METHODS: The EEG activity at the motor (MC) and frontal cortices was measured during an incremental exercise test (IET) in 11 cyclists (peak oxygen uptake VO2peak 4.1 ± 0.74 (SD) L min(-1)). EEG power spectral densities were calculated for alpha slow (αS) (8-10 Hz), alpha fast, (αF) (10-13 Hz), Beta (ß) (13-30 Hz), and Gamma (γ) (30-40 Hz). EEG data were calculated as % change from eyes open (EO) baseline and a repeated measures analysis of variance (ANOVA) was performed on regions of interest (ROI), time and bandwidth. RESULTS: All EEG activity increased from 50 % Vo2peak to ventilatory threshold (VT) (P = 0.045) and respiratory compensation point (RCP) (P = 0.019) and decreased from RCP to end of exercise (END) (P = 0.04). Significant differences between regions were found at the VLPFC and MC for both αS and αF. αS and αF increased from 50 % VO2peak to RCP (14.9 ± 10.2 to 23.8 ± 15.5 and 18.9 ± 10.6 to 26.12 ± 12.7, respectively) and then decreased to END (23.8 ± 15.5 to 14.4 ± 10.3 and 26.1 ± 12.7, to 17.7 ± 8.8, respectively) (P < 0.01) and concomitantly only decreased significantly in MC in αF from VT to END (P < 0.05). CONCLUSION: There is a decline in the EEG response to exercise in the PFC following the RCP, whilst alpha activity in the MC is preferentially maintained; therefore, changes within the PFC appear to play a role in exercise termination.

Perceptual and cerebro-spinal responses to graded innocuous and noxious stimuli following aerobic exercise.

AIM: The aim of this study was to evaluate the effect of aerobic exercise on perceptual and cerebro-spinal responses to graded electrocutaneous stimuli. METHODS: The design comprised 2 x 30 min of cycling exercise at 30% and 70% of peak oxygen consumption (VO2 peak) on separate occasions in a counter-balanced order in 10 healthy participants. Assessment of nociceptive withdrawal reflex threshold (NWR-T), pain threshold (PT), and somatosensory evoked potentials (SEPs) to graded electrocutaneous stimuli were performed before and after exercise. Perceptual magnitude ratings and SEPs were compared at 30%PT, 60%PT, 100%PT before (Pre), 5 min after (Post1), and 15 min after (Post2) aerobic exercise. RESULTS: There was no difference in the NWR-T and the PT following exercise at 30% and 70% of VO2 peak. ANOVA for the perceptual response within pooled electrocutaneous stimuli show a significant main effect for time (F2,18=5.41, P=0.01) but no difference for exercise intensity (F1,9=0.02, P=0.88). Within-subject contrasts reveal trend differences between 30%PT and 100%PT for Pre-Post1 (P=0.09) and Pre-Post2 (P=0.02). ANOVA for the SEPs peak-to-peak signal amplitude (N1-P1) show significant main effect for time (F2,18=4.04, P=0.04) but no difference for exercise intensity (F1,9=1.83, P=0.21). Pairwise comparisons for time reveal differences between Pre-Post1 (P=0.06) and Pre-Post2 (P=0.01). There was a significant interaction for SEPs N1-P1 between exercise intensity and stimulus intensity (F2,18=3.56, P=0.05). CONCLUSION: These results indicate that aerobic exercise did not increase the electrocutaneous threshold for pain and the NWR-T. Aerobic exercise attenuated perceptual responses to innocuous stimuli and SEPs N1-P1 response to noxious stimuli.

Exercise-induced dehydration does not alter time trial or neuromuscular performance.

This study examined the effect of exercise-induced dehydration by ~4% body mass loss on 5-km cycling time trial (TT) performance and neuromuscular drive, independent of hyperthermia. 7 active males were dehydrated on 2 occasions, separated by 7 d. Participants remained dehydrated (DEH, -3.8±0.5%) or were rehydrated (REH, 0.2±0.6%) over 2 h before completing the TT at 18-25 °C, 20-30% relative humidity. Neuromuscular function was determined before dehydration and immediately prior the TT. The TT started at the same core temperature (DEH, 37.3±0.3°C; REH, 37.0±0.2 °C (P>0.05). Neither TT performance (DEH, 7.31±1.5 min; REH, 7.10±1.3 min (P>0.05)) or % voluntary activation were affected by dehydration (DEH, 88.7±6.4%; REH, 90.6±6.1% (P>0.05)). Quadriceps peak torque was significantly elevated in both trials prior to the TT (P<0.05), while a 19% increase in the rate of potentiated peak twitch torque development (P<0.05) was observed in the DEH trial only. All other neuromuscular measures were similar between trials. Short duration TT performance and neuromuscular function are not reduced by dehydration, independent of hyperthermia.

Cold-water immersion decreases cerebral oxygenation but improves recovery after intermittent-sprint exercise in the heat.

This study examined the effects of post-exercise cooling on recovery of neuromuscular, physiological, and cerebral hemodynamic responses after intermittent-sprint exercise in the heat. Nine participants underwent three post-exercise recovery trials, including a control (CONT), mixed-method cooling (MIX), and cold-water immersion (10 °C; CWI). Voluntary force and activation were assessed simultaneously with cerebral oxygenation (near-infrared spectroscopy) pre- and post-exercise, post-intervention, and 1-h and 24-h post-exercise. Measures of heart rate, core temperature, skin temperature, muscle damage, and inflammation were also collected. Both cooling interventions reduced heart rate, core, and skin temperature post-intervention (P < 0.05). CWI hastened the recovery of voluntary force by 12.7 ± 11.7% (mean ± SD) and 16.3 ± 10.5% 1-h post-exercise compared to MIX and CONT, respectively (P < 0.01). Voluntary force remained elevated by 16.1 ± 20.5% 24-h post-exercise after CWI compared to CONT (P < 0.05). Central activation was increased post-intervention and 1-h post-exercise with CWI compared to CONT (P < 0.05), without differences between conditions 24-h post-exercise (P > 0.05). CWI reduced cerebral oxygenation compared to MIX and CONT post-intervention (P < 0.01). Furthermore, cooling interventions reduced cortisol 1-h post-exercise (P < 0.01), although only CWI blunted creatine kinase 24-h post-exercise compared to CONT (P < 0.05). Accordingly, improvements in neuromuscular recovery after post-exercise cooling appear to be disassociated with cerebral oxygenation, rather reflecting reductions in thermoregulatory demands to sustain force production.

The limits to exercise performance and the future of fatigue research.

The study of human fatigue stretches back centuries and remains a significant part of medical and social discourse. In the exercise sciences fatigue is routinely related to the ability to produce muscle force or to the recovery from force decrements. However, the study of fatigue has by virtue of the experimental paradigm excluded the subjective sense a person attributes to an event or experience, thus reducing our overall understanding of the fatigue process. Modern studies report the causes of fatigue as either central or peripheral in origin. Although useful, this dichotomy can also exclude the individual subjective assessment. Furthermore, adhering dogmatically to set parameters is likely limiting the advancement of our understanding. A more realistic paradigm would permit the individual to use the sensory cues to adjust the effort along with the fatigue process rather than rely purely on feedback mechanisms. Therefore, bringing feedforward mechanisms of the brain into fatigue research perhaps represents the next phase in the unravelling of the fatigue process.

Neuromuscular responses to hydration in moderate to warm ambient conditions during self-paced high-intensity exercise.

OBJECTIVE: To examine the neuromuscular responses to 60 minutes of self-paced high-intensity exercise punctuated with 6 × 1-minute "all-out" sprints at 10-minute intervals in moderate (19.8°C, SEM 0.3) and warm (33.2, SEM 0.1), humid (∼64% relative humidity) conditions with either complete hydration (CH) or without hydration (NF). DESIGN: Seven subjects (mean age 20.6 years (SE 1.1), mass 73.8 kg (SE 4.5), peak power 288 W (SE 11.3)) performed the time trial on four separate occasions, which were differentiated by ambient temperature and fluid ingestion. For each sprint interval, distance, power output and electromyographic (EMG) data from the rectus femoris and vastus lateralis muscles were recorded. RESULTS: The NF trials resulted in a reduction in body mass for the moderate and warm conditions of 1.7% and 2.1%, respectively. Final rectal temperatures were not different among conditions (∼38.7°C). Total body sweating was higher in the warm condition (19.1-21.3 ml/kg per hour) compared with the moderate condition (16.1-16.5 ml/kg per hour; p<0.05). Neither fluid ingestion nor ambient temperature altered total distance cycled for any of the trials (range 30.1-32.6 km). The normalised integrated EMG (as percentage of maximal voluntary contraction) when compared with the first sprint increased from sprint three for the rectus femoris muscle in both no and complete hydration but decreased for the vastus lateralis muscle. The mean percentile frequency shift increased for both the vastus lateralis and rectus femoris muscles in both no and complete hydration. CONCLUSIONS: These results suggest that the integrity of the neuromuscular system is adjusted according to hydration status and ambient temperatures during intense self-paced cycling.

Cerebral oxygenation decreases but does not impair performance during self-paced, strenuous exercise.

AIM: The reduction in cerebral oxygenation (Cox) is associated with the cessation of exercise during constant work rate and incremental tests to exhaustion. Yet in exercises of this nature, ecological validity is limited due to work rate being either fully or partly dictated by the protocol, and it is unknown whether cerebral deoxygenation also occurs during self-paced exercise. Here, we investigated the cerebral haemodynamics during a 5-km running time trial in trained runners. METHODS: Rating of perceived exertion (RPE) and surface electromyogram (EMG) of lower limb muscles were recorded every 0.5 km. Changes in Cox (prefrontal lobe) were monitored via near-infrared spectroscopy through concentration changes in oxy- and deoxyhaemoglobin (Delta[O(2)Hb], Delta[HHb]). Changes in total Hb were calculated (Delta[THb] = Delta[O(2)Hb] + Delta[HHb]) and used as an index of change in regional blood volume. RESULTS: During the trial, RPE increased from 6.6 +/- 0.6 to 19.1 +/- 0.7 indicating maximal exertion. Cox rose from baseline to 2.5 km ( upward arrowDelta[O(2)Hb], upward arrowDelta[HHb], upward arrowDelta[THb]), remained constant between 2.5 and 4.5 km, and fell from 4.5 to 5 km ( downward arrowDelta[O(2)Hb], upward arrowDelta[HHb], <-->Delta[THb]). Interestingly, the drop in Cox at the end of the trial coincided with a final end spurt in treadmill speed and concomitant increase in skeletal muscle recruitment (as revealed by higher lower limb EMG). CONCLUSION: Results confirm the large tolerance for change in Cox during exercise at sea level, yet further indicate that, in conditions of self-selected work rate, cerebral deoxygenation remains within a range that does not hinder strenuous exercise performance.

Reproducibility and changes in twitch properties associated with age and resistance training in young and elderly women.

We compared knee extensor twitch contractile properties (TP) between nine young women (YW, 20-30 years) and 10 elderly women (63-78 years) and examined changes associated with resistance training in addition to measurement reproducibility. Data were obtained on two occasions 3 weeks apart after which subjects performed bilateral leg extension and bilateral leg curl exercises 3 days/week for 10 weeks. TP demonstrated moderate to good reproducibility in both age groups with Pearson's r and the intra-class correlation coefficient ranging from 0.67 to 0.85 (P<0.05) and the technical error of the measurement ranging from 4.2% to 7.8%. Pre-training, peak twitch torque, rate of torque development, and the rate of relaxation were 24-32% greater for the YW than EW (P<0.05). Time to peak torque, half-relaxation time, and contraction duration were not significantly different between age groups. Post-training, changes of 2.6-6.1% were observed in TP; however, these changes were not significant in either group. These data suggest the presence of an age-associated slowing in the rate of muscle contraction. Furthermore, the lack of change in TP in both groups suggests resistance training failed to alter contractile function. However, these findings are discussed in relation to measurement reproducibility and the meaningfulness of the data obtained.

Normalized lengthening peak torque is associated with temporal twitch characteristics in elderly women but not young women.

AIM: To determine if greater normalized torque during maximal effort lengthening actions in elderly women compared with young women is related to age-associated adjustments in neural activation and/or contractile function. METHODS: The right knee extensors of 14 young women (21-30 years) and 12 elderly women (65-78 years) were assessed for isometric, shortening and lengthening peak torque, electromyography (EMG) activity, and isometric twitch contractile properties. Knee extensor contractile tissue volume was determined using magnetic resonance imaging. RESULTS: Normalized torque was determined as peak torque per unit of knee extensor contractile tissue volume. Normalized torque during the isometric and shortening actions was similar between age groups (P > 0.05); however, lengthening normalized torque was significantly higher for the elderly women (P < 0.05). In the young women, a significant relationship existed between normalized torque and EMG for all muscle actions (P < 0.05), while no association was found between normalized torque and temporal twitch characteristics for any muscle action (P > 0.05). In the elderly women, a significant relationship existed between normalized torque and EMG for the isometric and shortening muscle actions (P < 0.05), but not for lengthening normalized torque and EMG (P > 0.05). Furthermore, no association existed between isometric and shortening normalized torque, and temporal twitch characteristics in the elderly women (P > 0.05); however, a significant relationship existed between lengthening normalized torque, and the rate of relaxation and contraction duration (P < 0.05). CONCLUSIONS: The greater capacity to develop lengthening peak torque relative to contractile tissue volume in the elderly women appeared to be associated with age-related adjustments in the temporal twitch characteristics rather than neural activation.

The combined effects of hydration and exercise heat stress on choice reaction time.

The purpose of this investigation was to examine the combined effects of hydration and exercise heat stress on choice reaction time. On three separate occasions eight male subjects performed cycle exercise at approximately 70% of peak power output in warm, humid conditions (31 degrees C, 63% relative humidity) for a maximum of 90 min or until exhaustion. Throughout the trials, subjects ingested either a volume of water equal to fluid loss (100-FR), a volume equivalent to approximately 50% of fluid loss (50-FR), or no fluid (0-FR). A choice reaction time task was undertaken at rest, after 20 min of cycling, 40 min of cycling and at the conclusion of exercise. Mean reaction time for 100-FR was 342.2+/-8.2 ms, 352.4+/-7.5 ms for 50-FR and 345.6+/-8.4 ms for 0-FR and were not significantly different. Choice reaction time was facilitated as the duration of exercise progressed with reaction time at 40 min and conclusion stages of exercise faster than at rest (P<0.005). Choice reaction time and accuracy were affected by the number of choices, with choice reaction time increasing linearly with the number of choices (P<0.005) and rate of incorrect responses increasing in the 4-choice task compared to the 1-choice and 2-choice task (P<0.05). The results indicate that, in up to 90 min of exercise in warm, humid conditions, choice reaction time is not compromised by different levels of hydration.

Effect of deception of distance on prolonged cycling performance.

This study examined the effect of deception of distance end-point on prolonged cycling performance. 21 subjects were randomly allocated to three groups (n = 7 per group). Each group completed three self-paced time-trials separated by one day. Subjects were told that each trial was a 30-km time-trial and were required to complete the distance in the fastest time possible. Following the initial trial of 30 km, one group completed Trial 2 with a longer distance (long distance group; 36 km), another group with a shorter distance (24 km; short distance group), and the third group as control (30 km; control). Each group then completed a third time-trial of 30 km. At no time was the deception of distance in Trial 2 disclosed to the subjects, and all sources of physiological and mechanical feedback were withheld during the trials. Data from Trials 1 and 3 were analysed by repeated-measures analysis of covariance. Time to complete Trial 1 was similar among groups (approximately 65 min.). Following the deception in Trial 2 the time to complete the 30 km in Trial 3 was increased for the short distance group, decreased for the long distance group, whilst the time for the control group remained unchanged. The times to complete the 30 km on Trials 1 and 3 were matched by changes in power output throughout the trials. It is concluded that subjects deceived of the actual distance completed will complete the subsequent performance trial based on perceived effort rather than on actual distance.

A reproducible and variable intensity cycling performance protocol for warm conditions.

This study was undertaken to assess the reproducibility of a variable intensitycycling protocol using subjects of varying abilities, under warm humid conditions. Eleven subjects (Age 21.4+/-2.6 years; VO2peak 3.30+/-0.9 l x min(-1); peak power 322.8+/-86.3 W; mean+/-SD) performed a 60 min cycling trial punctuated with six one-min "all-out" sprints at 10-min intervals on three occasions 5-14 days apart. Ambient temperature and relative humidity were set at 33+/-0.7 degrees C and 63+/-2.0%, respectively. Subjects used their own bicycle mounted to an electromagnetic trainer and were only permitted to monitor elapsed time and heart rate. Repeatability was assessed using the limits of agreement which were best between trials 2 and 3 where the distance cycled was -0.54 km below and 1.34 km above the distance cycled for trial 2. The co-efficient of variation (CV) for distance for three trials was 3.58%. For trials 1 and 2 the CV was 3.54% (r = 0.97, p< 0.001) decreasing to 1.34% (r = 0.99, p< 0.001) for trials 2 and 3. The intra-class correlation for three trials was 0.93. Distance for trial 1 (26.3+/-5.0 km; p< 0.05) was less than trials 2 (27.7+/-5.7 km) and 3 (28.1+/-5.6 km). It was concluded that repeatability for this performance protocol with cyclists of varying abilities In warm humid conditions was acceptable given at least one familiarisation trial. However, it is not yet known whether other protocols designed for moderate environments are applicable to less favorable conditions. Further studies are needed before results of treatment effects under differing ambient conditions can be fully understood and assigned appropriate significance.

Methods, advantages, and limitations of body cooling for exercise performance.

Precooling studies confirm that increasing body heat is a limiting factor during exercise. However, it seems that precooling is only beneficial for endurance exercise of up to 30-40 minutes rather than intermittent or short duration exercise.

Whole-body pre-cooling does not alter human muscle metabolism during sub-maximal exercise in the heat.

Muscle metabolism was investigated in seven men during two 35 min cycling trials at 60% peak oxygen uptake, at 35 degrees C and 50% relative humidity. On one occasion, exercise was preceded by whole-body cooling achieved by immersion in water during a reduction in temperature from 29 to 24 degrees C, and, for the other trial, by immersion in water at a thermoneutral temperature (control, 34.8 degrees C). Pre-cooling did not alter oxygen uptake during exercise (P > 0.05), whilst the change in cardiac frequency and body mass both tended to be lower following pre-cooling (0.05 < P < 0.10). When averaged over the exercise period, muscle and oesophageal temperatures after pre-cooling were reduced by 1.5 and 0.6 degrees C respectively, compared with control (P < 0.05). Pre-cooling had a limited effect on muscle metabolism, with no differences between the two conditions in muscle glycogen, triglyceride, adenosine triphosphate, creatine phosphate, creatine or lactate contents at rest, or following exercise. These data indicate that whole-body pre-cooling does not alter muscle metabolism during submaximal exercise in the heat. It is more likely that thermoregulatory and cardiovascular strain are reduced, through lower muscle and core temperatures.

Evidence for neuromuscular fatigue during high-intensity cycling in warm, humid conditions.

The purpose of this study was to examine and describe the neuromuscular changes associated with fatigue using a self-paced cycling protocol of 60-min duration, under warm, humid conditions. Eleven subjects [mean (SE) age 21.8 (0.8) years; height 174.9 (3.0) cm; body mass 74.8 (2.7) kg; maximum oxygen consumption 50.3 (1.8) ml.kg.min-1] performed one 60-min self-paced cycling time trial punctuated with six 1-min "all out" sprints at 10-min intervals, while 4 subjects repeated the trial for the purpose of determining reproducibility. Power output, integrated electromyographic signal (IEMG), and mean percentile frequency shifts (MPFS) were recorded at the mid-point of each sprint. There were no differences between trials for EMG variables, distance cycled, mean heart rate, and subjective rating of perceived exertion for the subjects who repeated the trial (n = 4). The results from the repeated trials suggest that neuromuscular responses to self-paced cycling are reproducible between trials. The mean heart rate for the 11 subjects was 163.6 (0.71) beats.min-1. Values for power output and IEMG expressed as a percentage of that recorded for the initial sprint decreased during sprints 2-5, with normalised values being 94%, 91%, 87% and 87%, respectively, and 71%, 71%, 73%, and 77%, respectively. However, during the final sprint normalised power output and IEMG increased to 94% and 90% of initial values, respectively. MPFS displayed an increase with time; however, this was not significant (P = 0.06). The main finding of this investigation is the ability of subjects to return power output to near initial values during the final of six maximal effort sprints that were included as part of a self-paced cycling protocol. This appears to be due to a combination of changes in neuromuscular recruitment, central or peripheral control systems, or the EMG signal itself. Further investigations in which changes in multiple physiological systems are assessed systematically are required so that the underlying mechanisms related to the development of fatigue during normal dynamic movements such as cycling can be more clearly delineated.