Cardiopulmonary, blood metabolite and rating of perceived exertion responses to constant exercises performed at different intensities until exhaustion.

OBJECTIVE: This study analysed cardiopulmonary, metabolic and rating of perceived exertion (RPE) responses during exercise bouts performed below, at and above the second lactate threshold (LT2) intensity. METHODS: 10 healthy men performed constant workloads to exhaustion at the first lactate threshold (LT1), LT2 and 25% of the difference between LT2 and maximal aerobic power output (TW(25%)) identified during an incremental test. The time to exhaustion (TE) was 93.8 (18.0), 44.5 (16.0) and 22.8 (10.6) min at LT1, LT2 and TW(25%), respectively (p < 0.001). Metabolic and cardiopulmonary parameters and RPE data were time normalised to the exercise bout duration. The correlation between the slope of these variables and TE was calculated. RESULTS: Differences were found for respiratory exchange ratio (RER), RPE and potassium at LT1; RER, RPE, norepinephrine and potassium at LT2; and ventilation, respiratory rate (RR), RPE, lactate and potassium at TW(25%). Except for RR, no cardiopulmonary or metabolic parameter increased significantly after 50% of the exercise duration, indicating a physiological steady state. VO2, heart rate and lactate at exhaustion in all exercise bouts were significantly lower than values reached in the maximal incremental test. The slope of most metabolic variables was not correlated to TE in LT1, LT2 and TW(25%), whereas the slope of RPE was significantly correlated to TE (r = -0.72 to -0.84; p < 0.05) for the three exercise intensities. CONCLUSION: Contrary to traditional suggestions, exercise at LT1, LT2 and TW(25%) intensities is performed and terminated in the presence of an overall physiological steady state.

The influence of peripheral afferent signals on the rating of perceived exertion and time to exhaustion during exercise at different intensities.

This study determined which peripheral variables would better predict the rating of perceived exertion (RPE) and time to exhaustion (TE) during exercise at different intensities. Ten men performed exercises at first lactate threshold (LT1), second lactate threshold (LT2), 50% of the distance from LT1 to LT2 (TT(50%) ), and 25% of the distance from LT2 to maximal power output (TW(25%) ). Lactate, catecholamines, potassium, pH, glucose, V(·)O2, VE, HR, respiratory rate (RR) and RPE were measured and plotted against the exercise duration for the slope calculation. Glucose, dopamine, and noradrenaline predicted RPE in TT(50%) (88%), LT2 (64%), and TW(25%) (77%), but no variable predicted RPE in LT1. RPE (55%), RPE+HR (86%), and RPE+RR (92% and 55%) predicted TE in LT1, TT(50%) , LT2, and TW(25%) , respectively. At intensities from TT(50%) to TW(25%) , variables associated with brain activity seem to explain most of the RPE slope, and RPE (+HR and+RR) seems to predict the TE.

Ventilation behavior during upper-body incremental exercise.

This study tested the ventilation (VE) behavior during upper-body incremental exercise by mathematical models that calculate 1 or 2 thresholds and compared the thresholds identified by mathematical models with V-slope, ventilatory equivalent for oxygen uptake (VE/V(O2)), and ventilatory equivalent for carbon dioxide uptake (VE/V(CO2)). Fourteen rock climbers underwent an upper-body incremental test on a cycle ergometer with increases of approximately 20 W · min(-1) until exhaustion at a cranking frequency of approximately 90 rpm. The VE data were smoothed to 10-second averages for VE time plotting. The bisegmental and the 3-segmental linear regression models were calculated from 1 or 2 intercepts that best shared the VE curve in 2 or 3 linear segments. The ventilatory threshold(s) was determined mathematically by the intercept(s) obtained by bisegmental and 3-segmental models, by V-slope model, or visually by VE/V(O2) and VE/V(CO2). There was no difference between bisegmental (mean square error [MSE] = 35.3 ± 32.7 l · min(-1)) and 3-segmental (MSE = 44.9 ± 47.8 l · min(-1)) models in fitted data. There was no difference between ventilatory threshold identified by the bisegmental (28.2 ± 6.8 ml · kg(-1) · min(-1)) and second ventilatory threshold identified by the 3-segmental (30.0 ± 5.1 ml · kg(-1) · min(-1)), VE/V(O2) (28.8 ± 5.5 ml · kg(-1) · min(-1)), or V-slope (28.5 ± 5.6 ml · kg(-1) . min(-1)). However, the first ventilatory threshold identified by 3-segmental (23.1 ± 4.9 ml · kg(-1) · min(-1)) or by VE/V(O)2 (24.9 ± 4.4 ml · kg(-1) · min(-1)) was different from these 4. The VE behavior during upper-body exercise tends to show only 1 ventilatory threshold. These findings have practical implications because this point is frequently used for aerobic training prescription in healthy subjects, athletes, and in elderly or diseased populations. The ventilatory threshold identified by VE curve should be used for aerobic training prescription in healthy subjects and athletes.

Low carbohydrate diet affects the oxygen uptake on-kinetics and rating of perceived exertion in high intensity exercise.

The aim of this study was to determine if the carbohydrate (CHO) availability alters the rate of increase in the rating of perceived exertion (RPE) during high intensity exercise and whether this would be associated with physiological changes. Six males performed high intensity exercise after 48 h of controlled, high CHO (80%) and low CHO (10%) diets. Time to exhaustion was lower in the low compared to high CHO diet. The rate of increase in RPE was greater and the VO2 slow component was lower in the low CHO diet than in the control. There was no significant condition effect for cortisol, insulin, pH, plasma glucose, potassium, or lactate concentrations. Multiple linear regression indicated that the total amplitude of VO2 and perceived muscle strain accounted for the greatest variance in the rate of increase in RPE. These results suggest that cardiorespiratory variables and muscle strain are important afferent signals from the periphery for the RPE calculations.