Sweat gland density and response during high-intensity exercise in athletes with spinal cord injuries.

Sweat production is crucial for thermoregulation. However, sweating can be problematic for individuals with spinal cord injuries (SCI), as they display a blunting of sudomotor and vasomotor responses below the level of the injury. Sweat gland density and eccrine gland metabolism in SCI are not well understood. Consequently, this study examined sweat lactate (S-LA) (reflective of sweat gland metabolism), active sweat gland density (SGD), and sweat output per gland (S/G) in 7 SCI athletes and 8 able-bodied (AB) controls matched for arm ergometry VO2peak. A sweat collection device was positioned on the upper scapular and medial calf of each subject just prior to the beginning of the trial, with iodine sweat gland density patches positioned on the upper scapular and medial calf. Participants were tested on a ramp protocol (7 min per stage, 20 W increase per stage) in a common exercise environment (21±1°C, 45-65% relative humidity). An independent t-test revealed lower (p<0.05) SGD (upper scapular) for SCI (22.3 ±14.8 glands · cm(-2)) vs. AB. (41.0 ± 8.1 glands · cm(-2)). However, there was no significant difference for S/G between groups. S-LA was significantly greater (p<0.05) during the second exercise stage for SCI (11.5±10.9 mmol · l(-1)) vs. AB (26.8±11.07 mmol · l(-1)). These findings suggest that SCI athletes had less active sweat glands compared to the AB group, but the sweat response was similar (SLA, S/G) between AB and SCI athletes. The results suggest similar interglandular metabolic activity irrespective of overall sweat rate.

Evaluation of artificial sweat in athletes with spinal cord injuries.

Athletes with spinal cord injury often experience high heat storage due to reduced sweating capacity below the spinal injury. Spray bottle (SB) may be used to apply mist for evaporative cooling during breaks in competitions. This study examined the efficacy of SB during rest breaks. Seven participants, four female and three males, (mean +/- SD age 24 +/- 4.1 year, weight 56.2 +/- 7.0 kg, upper-body VO(2) peak 2.4 +/- 0.6 l/min) volunteered for the study. Participants were paraplegic athletes (T3-T12/L1) with both complete and incomplete lesions. Participants arm-cranked using a ramp protocol in an environment of 21 +/- 1.5 degrees C and 55 +/- 3% rh once using a SB during 1-min rest between 7-min stages of increasing intensity and once without the SB (CON). Mean total work was similar (p = 0.86) for the SB and CON (2495.7 +/- 914.6 vs. 2407.1 +/- 982.3 kJ, respectively). Likewise, the mean work times were similar between trials (27 +/- 6 and 26 +/- 7 min for SB and CON, respectively). Furthermore, there were no significant differences detected between trials for skin temperature, rectal temperature, esophageal temperature (p > 0.05). There were no statistically significant differences detected between trials for RPE (p > 0.05). In conclusion, the application of artificial sweat via SB was ineffective in attenuating the onset of uncompensable heat strain during high-intensity arm exercise in a comfortable environment.

RPE drift during cycling in 18 degrees C vs 30 degrees C wet bulb globe temperature.

AIM: The potential influence of a hotter vs cooler environment on ratings of perceived exertion (RPE) estimations during longer duration exercise is not well-understood. This study compared overall and differentiated RPEs during cycling in 18 degrees C vs 30 degrees C wet bulb globe temperature (WBGT). METHODS: Male volunteers (n=16) completed a maximal cycling trial (60 rev . min(-1), 25 Watts . min(-1)) to determine VO(2) max and ventilatory threshold (VT) before completing 2 (counterbalanced) longer duration cycling trials. At 30 degrees C WBGT (30C) and 18 degrees C WBGT (18C), subjects cycled 60 min (60 rev . min(-1), 90% individualized VT). Heart rate (HR, b . min(-1)) and rectal temperature (Tre, degrees C) were recorded every 5 min with corresponding RPE-overall (RPE-O), RPE-legs (RPE-L) and RPE-chest (RPE-C) estimations. RESULTS: HR was not significantly different at 5 min but was greater (P<0.05) for 30C at all other time points. During 30C, Tre was significantly greater (25, 30, 35, 40, 45, 50, 55 and 60 min), RPE-O was significantly greater (5, 40, 45, 50, 55 and 60 min), RPE-L was significantly greater (55 and 60 min) and RPE-C was significantly greater (35, 40, 45, 50, 55 and 60 min). CONCLUSIONS: Greater cardiovascular (HR) and thermal (Tre) strain partially explain greater perceptual ratings during 30C. Discernible RPE differences resulted mid-way through 60 min cycling with minimal differences initially. Results suggest RPEs are magnified in a 30 degrees C (vs 18 degrees C) environment beyond 30 min duration. Additionally, a 30 degrees C environment resulted in a less pronounced impact on RPE-L (vs RPE-C and RPE-O).

Influence of aerobic fitness on ratings of perceived exertion during graded and extended duration cycling.

AIM: Ratings of perceived exertion (RPE) have been shown similar across subjects of varying fitness when estimations are made at relative physiological criteria. Because few studies have investigated the influence of fitness during longer duration bouts, the current investigation compared overall exertion (RPE-O), leg exertion (RPE-L) and breathing/chest exertion (RPE-C) between aerobically fit and unfit subjects. METHODS: Aerobically fit (61.6+/-2.5 mL . kg . min(-1)) (n=7) and unfit (41.8+/-6.3 mL . kg . min(-1)) (n=6) males completed a maximal bike test and then cycled for 60 min at approximately 90% of individualized ventilatory threshold (VT) (V(E)/VO(2) vs V(E)/VCO(2)). Heart rate (HR, b . min(-1)), rectal temperature (Tre, degrees C) and RPE estimations were collected during graded testing every 2 min and every 10 min during 60 min bouts. RESULTS: During graded testing, RPE estimations at VT were not significantly different between groups. During 60 min cycling, HR and Tre were not significantly different between groups. Also, there were no significant differences for HR increase (HR 60 min HR 5 min) or Tre increase (Tre 60 min Tre 5 min). Interactions between groups were; RPE-O (P=0.09), RPE-L (P=0.06) and RPE-C (P=0.19). Analyses suggest groups experienced similar relative cardiovascular (HR) and thermal (Tre) strain. CONCLUSIONS: Although RPE responses between groups were similar at 10, 20 and 30 min, RPE drift was magnified in aerobically unfit subjects (vs aerobically fit subjects) beyond the 30 min point. Contrary to previous studies suggesting aerobic fitness does not influence RPE, current results show lower aerobic fitness magnifies RPE at individualized relative intensities when cycling extends beyond 30 min.

RPE-lactate dissociation during extended cycling.

This study examined the association of blood lactate concentration [La] and heart rate (HR) with ratings of perceived exertion (RPE) during 60 min of steady workload cycling. Physically active college-aged subjects (n = 14) completed an exhaustive cycling test to determine VO(2) (peak) and lactate threshold (2.5 mmol l(-1)). Subjects then cycled for 60 min at the power output associated with 2.5 mmol l(-1) [LA]. HR, [LA], RPE-overall, RPE-legs and RPE-chest were recorded at 5, 10, 20, 30, 40, 50 and 60 min. The 60-min trials were below maximal lactate steady state, with peak lactate concentration occurring at 20 min after which [LA] declined. The 20-min point was therefore considered pivotal, and data at other points were compared to this time point. Repeated measures ANOVA with simple contrasts (alpha = 0.05) showed (a) [LA] at 40, 50 and 60 min was significantly lower than at 20 min, (b) RPE-O and RPE-L were significantly greater at 30, 40, 50 and 60 min than at 20 min, (c) RPE-C was significantly greater at 40, 50 and 60 min than at 20 min, and (d) HR was significantly greater at 30, 40, 50 and 60 min than at 20 min. Significant (P < 0.05) positive correlations were found between HR and RPE-O (r = 0.43), RPE-L (r = 0.48) and RPE-C (r = 0.41) while correlations for [LA]-HR (r = 0.13) and [LA]-RPE (RPE-O: r = -0.11, RPE-L: r = 0.01, RPE-C: r = -0.06) were weak and non-significant. There is a dissociation of RPE and [LA] owing to RPE drift and lactate kinetics in longer duration sub-maximal exercise. Apparently, [LA] is not a strong RPE mediator during extended cycling.

Sweat lactate response during cycling at 30 degrees C and 18 degrees C WBGT.

Sweat lactate reflects eccrine gland metabolism. However, the metabolic tendencies of eccrine glands in a hot versus thermoneutral environment are not well understood. Sixteen male volunteers completed a maximal cycling trial and two 60-min cycling trials [30 degrees C = 30 +/- 1 degrees C and 18 degrees C = 18 +/- 1 degrees C wet bulb globe temperature (WBGT)]. The participants were requested to maintain a cadence of 60 rev min(-1) with the intensity individualized at approximately 90% of the ventilatory threshold. Sweat samples at 10, 20, 30, 40, 50 and 60 min were analysed for lactate concentration. Sweat rate at 30 degrees C (1380 +/- 325 ml x h(-1)) was significantly greater (P < 0.05) than at 18 degrees C (632 +/- 311 ml x h(-1)). Sweat lactate concentration was significantly greater (P < 0.05) at each time point during the 18 degrees C trial, with values between trials tending to converge across time. During the 30 degrees C trial, both heart rate (20, 30, 40, 50 and 60 min) and rectal temperature (30, 40, 50 and 60 min) were significantly higher than in the 18 degrees C trial. Higher sweat lactate concentrations coupled with lower sweat rates may indicate a greater relative contribution of oxygen-independent metabolism within eccrine glands during exercise at 18 degrees C. Decreases in sweat lactate concentration across time suggest either greater dilution due to greater sweat volume or increased reliance on aerobic metabolism within eccrine glands. The convergence of lactate concentrations between trials may indicate that time-dependent modifications in sweat gland metabolism occur at different rates contingent partially on environmental conditions.

Sweat lactate response between males with high and low aerobic fitness.

Sweat lactate indirectly reflects eccrine gland metabolism. However the potential influence of aerobic fitness on sweat lactate is not well-understood. Six males with high aerobic fitness [peak oxygen consumption ( VO(2)peak): 61.6 (2.5) ml.kg(-1).min(-1)] and seven males with low aerobic fitness [ VO(2)peak: 41.8 (6.4) ml.kg(-1).min(-1)] completed a maximal exertion cycling trial followed on a different day by 60 min of cycling (60 rev.min(-1)) in a 30 degrees C wet bulb globe temperature environment. Intensity was individualized at 90% of the ventilatory threshold ( V(E)/ VO(2) increase with no concurrent V(E)/ VCO(2) increase). Sweat samples were collected from the lumbar region every 10 min and analyzed for lactate concentration. Sweat rate (SR) was significantly greater ( p<0.05) for subjects with a high [1445 (254) ml.h(-1)] versus a low [1056 (261) ml.h(-1)] fitness level. Also, estimated total lactate excretion (SRxmean sweat lactate concentration) was marginally greater ( p=0.2) in highly fit males. However, repeated measures ANOVA showed no significant differences ( p>0.05) between groups for sweat lactate concentration at any time point. Current results show highly fit (vs. low fitness level) males have a greater sweat rate which is consistent with previous literature. However aerobic fitness and subsequent variations in SR do not appear to influence sweat lactate concentrations in males.