The development of rating of perceived exertion-based tests of physical working capacity

The purpose of the present study was to use ratings of perceived exertion (RPE) from the Borg (6-20) and OMNI-Leg (0-10) scales to determine the Physical Working Capacity at the Borg and OMNI thresholds (PWC(BORG) and PWC(OMNI)). PWC(BORG) and PWC(OMNI) were compared with other fatigue thresholds determined from the measurement of heart rate (the Physical Working Capacity at the Heart Rate Threshold: PWC(HRT)), and oxygen consumption (the Physical Working Capacity at the Oxygen Consumption Threshold, PWC(VO2)), as well as the ventilatory threshold (VT). Fifteen men and women volunteers (mean age +/- SD = 22 +/- 1 years) performed an incremental test to exhaustion on an electronically braked ergometer for the determination of VO2 peak and VT. The subjects also performed 4 randomly ordered workbouts to exhaustion at different power outputs (ranging from 60 to 206W) for the determination of PWC(BORG), PWC(OMNI), PWC(HRT), and PWC(VO2). The results indicated that there were no significant mean differences among the fatigue thresholds: PWC(BORG) (mean +/- SD = 133 +/- 37W; 67 +/- 8% of VO2 peak), PWC(OMNI) (137 +/- 44W; 68 +/- 9% of VO2 peak), PWC(HRT) (135 +/- 36W; 68 +/- 8% of VO2 peak), PWC(VO2) (145 +/- 41W; 72 +/- 7% of VO2 peak) and VT (131 +/- 45W; 66 +/- 8% of VO2 peak). The results of this study indicated that the mathematical model used to estimate PWC(HRT) and PWC(VO2) can be applied to ratings of perceived exertion to determine PWC(BORG) and PWC(OMNI) during cycle ergometry. Salient features of the PWC(BORG) and PWC(OMNI) tests are that they are simple to administer and require the use of only an RPE scale, a stopwatch, and a cycle ergometer. Furthermore, the power outputs at the PWC(BORG) and PWC(OMNI) may be useful to estimate the VT noninvasively and without the need for expired gas analysis.     

Neural control of the forearm cutaneous vasoconstrictor response to dynamic exercise.

This study was designed to evaluate the relative importance of intended effort ("central command") and of the absolute intensity of dynamic exercise to the cutaneous vasoconstrictor response to the onset of exercise in humans. Skin blood flow (laser-Doppler flowmetry) was measured from the forearm in six healthy individuals during 3-min periods of high- and low-intensity exercise with and without partial neuromuscular blockade. Cutaneous vascular conductance (CVC) was calculated from the ratio of skin blood flow to mean arterial pressure and expressed as a percent change from rest. A rating of perceived exertion (RPE) was expressed as a subjective measure of intended effort. Under control conditions, CVC decreased by 22% (median; range 7-42%, P less than 0.05) during high-intensity exercise [218 (186-268) W; RPE 16 (14-19) exertion units]. In contrast, during control low-intensity exercise [106 (88-128) W; RPE 10 (9-14) exertion units], during low-level exercise with curare [77 (54-98) W; RPE 13 (11-16) exertion units], and during maximal exercise with curare [106 (88-124) W; RPE 19 (18-20) exertion units], CVC did not change significantly. These results suggest that factors related to the activity of the exercising muscle and its metabolism rather than intended effort determine the cutaneous vasoconstrictor response to the initiation of intense dynamic exercise in humans.     

Ratings of perceived exertion and muscle activity during the bench press exercise in recreational and novice lifters

This study examined ratings of perceived exertion (RPE) and electromyography (EMG) during resistance exercise in recreational and novice lifters. Fourteen novice (age = 21.5 +/- 1.5 years) and 14 recreationally trained (age = 21.9 +/- 2.2 years) women volunteered to perform the bench press exercise at 60 and 80% of their 1 repetition maximum (1RM). RPE and EMG were measured during both intensities. Statistical analyses revealed that active muscle RPE increased as resistance exercise intensity increased from 60% 1RM to 80% 1RM (12.32 +/- 1.81 vs. 15.14 +/- 1.74). Integrated EMG also increased as resistance exercise intensity increased from 60% 1RM to 80% 1RM (in the pectoralis major; 98.62 +/- 17.54 vs. 127.98 +/- 29.02). No significant differences in RPE or EMG were found between novice and recreational lifters. These results indicate that RPE is related to the relative exercise intensity lifted as well as muscle activity during resistance exercise for both recreational and novice lifters. These results support the use of RPE as a method of resistance exercise intensity estimation for both types of lifters.     

Heart rate at lactate threshold and cycling time trials

The purpose of this investigation was to relate the heart rate and lactate response during simulated cycling time trials to incremental laboratory tests. Subjects (N = 10) were tested for .V(O2)max (56.1 +/- 2.4 ml.kg(-1).min(-1) ) and lactate threshold during incremental tests to exhaustion. Power output and heart rate (HR) at threshold was assessed by 3 methods: lactate deflection point (LaT), onset of blood lactate accumulation (OBLA), and the point on the lactate curve at maximal distance from a line connecting starting and finishing power output (Dmax). Power output determined at these thresholds was 282.1 +/-4.2, 302.5 +/-1.3, and 296.0 +/- 1.8 W, respectively, whereas HR was determined to be 88.6 +/- 0.01, 92.2 +/- 0.01, and 91.0 +/- 0.01% of maximum, respectively. Power output and HR were significantly lower for LaT than for the other 2 methods (p < 0.05). On separate visits, cyclists were instructed to perform maximum efforts for 30 and 60 minutes (30TT and 60TT). Lactate, HR, perceived exertion (RPE), and metabolic variables were measured during the time trials. During the 30TT, participants sustained a significantly higher lactate level (5.29 +/- 0.3 vs. 3.43 +/- 0.3 mmol.L(-1), p < 0.001), percentage of maximum HR (%HRmax) (90.3 +/- 0.02 vs. 84.6 +/- 0.01, p = 0.009), and overall RPE (15.5 +/- 0.5 vs. 14.4 +/- 0.5, p = 0.009), than during the 60TT. .V(O2) was not significantly different between the time trials; however, .V(CO2) (p = 0.008), ventilation (p = 0.004), and respiratory exchange ratio (p = 0.02) were significantly higher during the 30TT. Correlations were found between HR at LaT (r = 0.78), OBLA (r = 0.78), and Dmax (r = 0.71) for the 60TT, but not for the 30TT. These data suggest that despite a large variability in blood lactate during time trial efforts of 30 and 60 minutes (from 1.8 to 10.8 mmol.L(-1)), HR was consistently 90% of maximum for the 30TT and 85% for the 60TT. HR during the 30TT was approximated by HR corresponding to OBLA and Dmax, whereas HR during 60TT was approximated by LaT.     

Perceived exertion is associated with an altered brain activity during exercise with progressive hyperthermia.

The present study tested the hypothesis that perceived exertion during prolonged exercise in hot environments is associated with changes in cerebral electrical activity rather than changes in the electromyogram (EMG) of the exercising muscles. Therefore, electroencephalogram (EEG) in three positions (frontal, central, and occipital cortex), EMG, rating of perceived exertion (RPE), and core temperature were measured in 14 subjects during submaximal exercise in normal (18 degrees C, control) and hot (40 degrees C, hyperthermia) environments. RPE increased from 11 +/- 1 units at 5 min to 20 +/- 0 units at exhaustion (50 +/- 3 min) in the trial with progressive hyperthermia, whereas exercise in the control trial was maintained with a stable core temperature for 1 h without exhausting the subjects. Altered EEG activity was observed in all electrode positions, and stepwise forward-regression analysis identified core temperature and a frequency index of the EEG over the frontal cortex as the best predictors of RPE. In contrast, there were no significant correlations between RPE and any of the measured EMG parameters (median spectral frequency, root mean square, or amplitude), and the EMG parameters were not different in hyperthermia compared with control. Thus hyperthermia does not seem to affect the activation pattern of the muscles. Rather, the linear correlation among core temperature, EEG frequency index, and RPE indicates that alterations in cerebral activity may be associated with the hyperthermia-induced development of fatigue during prolonged exercise in hot environments.     

Training state improves the relationship between rating of perceived exertion and relative exercise volume during resistance exercises

ABSTRACT: Testa, M, Noakes, TD, and Desgorces, F-D. Training state improves the relationship between rating of perceived exertion and relative exercise volume during resistance exercises. J Strength Cond Res 26(11): 2990-2996, 2012-The aim of this study was to investigate how the rating of perceived exertion (RPE) during resistance exercises was influenced by the exercise volume and athletes' training state. Eighty physical education students (well trained, less well trained, and novices) rated their perceived exertion of multilift sets using the category-ratio scale. These sets were performed with moderate (60-80% of 1-repetition maximum [1RM]) and heavy loads (80-100% of 1RM) involving low volume of exercise (5.5 ± 1.1 reps for moderate and 1.3 ± 0.4 reps for the heavy load) and high volume of exercise (moderate load: 17.5 ± 2.1 reps; high load: 2.9 ± 0.6 reps). The exercise volume of the sets was expressed relatively to individual maximal capacities using the maximum number of repetition (MNR) for the load lifted. General linear model describes that RPE was related to MNR % with a training state effect (p < 0.01) observed only for sets involving a low MNR % and without effect of absolute volume and exercise intensity (high MNR sets: adjusted R = 0.65 and 0.78 and low MNR sets adjusted R = 0.37 and 0.34 in low MNR tests). High standard errors of estimated relative volume appeared when using the RPE from low exercise volume sets (12.8 and 14.4% of actual relative volume). Coaches should consider the RPE resulting from high exercise-induced physical strain to estimate the actual relative volume and to estimate the individual MNR at a given load.     

Estimation of oxygen uptake from heart rate and ratings of perceived exertion in young soccer players

The objective of this study was to estimate the oxygen uptake (&OV0312;O2) in elite youth soccer players using measures of heart rate (HR) and ratings of perceived exertion (RPEs). Forty-six regional-level male youth soccer players (～13 years) participated in 2 VO(2)max tests. Data for HR, RPE, and VO(2) were simultaneously recorded during the VO(2)max tests with incremental running speed. Regression equations were derived from the first VO(2)max test. Two weeks later, all players performed the same VO(2)max test to validate the developed regression equations. There were no significant differences between the estimated values in the first test and actual values in the second test. During the continuous endurance exercise, the combination of percentage of maximal HR (%HRmax) and RPE measures gave similar estimation of %VO(2)max (R = 83%) in comparison to %HRmax alone (R = 81%). However, the estimation of VO(2) using combined %HRmax and RPE was not satisfactory (R = 45-46%). Therefore, the use of %HRmax (without RPE) to estimate %VO(2)max could be a useful tool in young soccer players during field-based continuous endurance testing and training. Specifically, coaches can use the %HRmax to quantify internal loads (%VO(2)max) and subsequently implement continuous endurance training at appropriate intensities. Furthermore, it seems that RPE is more useful as a measure of internal load during noncontinuous (e.g., intermittent and sprint) exercises but not to estimate %VO(2)max during continuous aerobic exercise (R = 59%).     

Maximal lactate steady-state prediction through quadratic modeling of selected stages of the lactate minimum test

In this study, we compared the maximal lactate steady state (MLSS) with lactate minimal (LM) intensities determined visually and through a quadratic polynomial function of selected stages of LM test. Eleven male recreational cyclists (27.7 +/- 4.5 years, 175.7 +/- 5.6 cm, 69.5 +/- 10.8 kg, and 12.0 +/- 5.5% body fat) performed one LM test under previous induction of hyperlactaemia with an initial intensity of 75 W with 30-W increments every 3 minutes with blood lactate concentration (HLa) and rating of perceived exertion (RPE) measurements. The LM intensity was determined visually (VLM) and by modeling the lactate response through polynomial function by using: 1) all stages (LMP); 2) the first stage, the stage corresponding to RPE-13 and the last stage/exhaustion (LMP3max); 3) the three lowest lactate concentration stages (LMP3adj); and 4) the initial, RPE-13, and RPE-16 stages (LMP3sub). The MLSS was determined as the highest intensity at a variation not greater than 0.05 mmol.l.min of HLa during the last 20 minutes of a 30-minute exercise session. The MLSS (204.0 +/- 16.0 W), VLM (198.6 +/- 15.2 W), LMP3adj (190.4 +/- 12.9 W), and LMP3sub (192.1 +/- 27.2 W) were not different, well correlated, and in agreement to each other. In conclusion, the polynomial modeling of HLa response to three submaximal stages produced exercise intensities that did not differ from MLSS.     

Monitoring exercise intensity during resistance training using the session RPE scale

This study investigated the reliability of the session rating of perceived exertion (RPE) scale to quantify exercise intensity during high-intensity (H), moderate-intensity (M), and low-intensity (L) resistance training. Nine men (24.7 +/- 3.8 years) and 10 women (22.1 +/- 2.6 years) performed each intensity twice. Each protocol consisted of 5 exercises: back squat, bench press, overhead press, biceps curl, and triceps pushdown. The H consisted of 1 set of 4-5 repetitions at 90% of the subject's 1 repetition maximum (1RM). The M consisted of 1 set of 10 repetitions at 70% 1RM, and the L consisted of 1 set of 15 repetitions at 50% 1RM. RPE was measured following the completion of each set and 30 minutes postexercise (session RPE). Session RPE was higher for the H than M and L exercise bouts (p < or = 0.05). Performing fewer repetitions at a higher intensity was perceived to be more difficult than performing more repetitions at a lower intensity. The intraclass correlation coefficient for the session RPE was 0.88. The session RPE is a reliable method to quantify various intensities of resistance training.     

Effect of alcohol on perceived exertion in relation to heart rate and blood lactate

The purpose of the study was to determine whether the perception of exertion is affected by alcohol during physical performance and whether altered self-rating of exertion is the result of an altered perception per se or of an altered physical capacity to perform work. Ten healthy men participated. Each subject was his own control and received an alcohol dose corresponding to 1 g.kg-1 body mass in 40% solution in the experimental session. The exercise test was performed on a cycle ergometer with an initial intensity of 50 W which was increased stepwise by 50 W at 4-min intervals up to near-maximal. The rating of perceived exertion (RPE) did not differ between alcohol and control sessions. Alcohol induced a significant increase in heart rate during exercise at 50 W (delta x = 8 beats.min-1) and at 100 W (delta x = 10 beats.min-1), while the change at higher intensities was insignificant. The systolic blood pressure and the blood lactate concentration were not significantly changed by alcohol. It is concluded that a moderate dose of alcohol does not alter RPE during physical exercise either per se or secondarily to an altered physical capacity to perform work.     

Hypnotic manipulation of effort sense during dynamic exercise: cardiovascular responses and brain activation.

The purpose of this investigation was to hypnotically manipulate effort sense during dynamic exercise and determine whether cerebral cortical structures previously implicated in the central modulation of cardiovascular responses were activated. Six healthy volunteers (4 women, 2 men) screened for high hypnotizability were studied on 3 separate days during constant-load exercise under three hypnotic conditions involving cycling on a 1) perceived level grade, 2) perceived downhill grade, and 3) perceived uphill grade. Ratings of perceived exertion (RPE), heart rate (HR), blood pressure (BP), and regional cerebral blood flow (rCBF) distributions for several sites were compared across conditions using an analysis of variance. The suggestion of downhill cycling decreased both the RPE [from 13 +/- 2 to 11 +/- 2 (SD) units; P < 0.05] and rCBF in the left insular cortex and anterior cingulate cortex, but it did not alter exercise HR or BP responses. Perceived uphill cycling elicited significant increases in RPE (from 13 +/- 2 to 14 +/- 1 units), HR (+16 beats/min), mean BP (+7 mmHg), right insular activation (+7.7 +/- 4%), and right thalamus activation (+9.2 +/- 5%). There were no differences in rCBF for leg sensorimotor regions across conditions. These findings show that an increase in effort sense during constant-load exercise can activate both insular and thalamic regions and elevate cardiovascular responses but that decreases in effort sense do not reduce cardiovascular responses below the level required to sustain metabolic needs.     

A lower-extremities kinematic comparison of deep-water running styles and treadmill running

The purpose of this investigation was to identify a deep-water running (DWR) style that most closely approximates terrestrial running, particularly relative to the lower extremities. Twenty intercollegiate distance runners (women, N = 12; men, N = 8) were videotaped from the right sagittal view while running on a treadmill (TR) and in deep water at 55-60% of their TR VO(2)max using 2 DWR styles: cross-country (CC) and high-knee (HK). Variables of interest were horizontal (X) and vertical (Y) displacement of the knee and ankle, stride rate (SR), VO(2), heart rate (HR), and rating of perceived exertion (RPE). Multivariate omnibus tests revealed statistically significant differences for RPE (p < 0.001). The post hoc pairwise comparisons revealed significant differences between TR and both DWR styles (p < 0.001). The kinematic variables multivariate omnibus tests were found to be statistically significant (p < 0.001 to p < 0.019). The post hoc pairwise comparisons revealed significant differences in SR (p < 0.001) between TR (1.25 +/- 0.08 Hz) and both DWR styles and also between the CC (0.81 +/- 0.08 Hz) and HK (1.14 +/- 0.10 Hz) styles of DWR. The CC style of DWR was found to be similar to TR with respect to linear ankle displacement, whereas the HK style was significantly different from TR in all comparisons made for ankle and knee displacement. The CC style of DWR is recommended as an adjunct to distance running training if the goal is to mimic the specificity of the ankle linear horizontal displacement of land-based running, but the SR will be slower at a comparable percentage of VO(2)max.     

Effect of training on the rating of perceived exertion at the ventilatory threshold

The purpose of this study was to determine the effect of training on the rating of perceived exertion (RPE) at the ventilatory threshold. College students were assigned to either training (n = 17) or control (n = 10) groups. Trainers completed 18 interval training sessions (five X 5 min cycling at 90-100% VO2max) and 8 continuous training sessions (40 min running or cycling) in 6 weeks. Pre- and post-training, cardiorespiratory, metabolic, and perceptual variables were measured at the ventilatory threshold during graded exercise tests on a cycle ergometer. Ventilatory threshold was that point above which VE X VO2-1 increased abruptly relative to work rate. Post-training means of trained and control subjects were compared using analysis of covariance, with pre-training values as covariates. Following training, the adjusted means for the trained subjects were significantly greater (p less than 0.05) than for controls for VO2max (6%), and for work rate (20%), VO2 (23%), and %VO2max (13%) at the ventilatory threshold. However, adjusted means for RPE at the ventilatory threshold were not significantly different (2%). Both before and after training, exercise at the ventilatory threshold was perceived as 'somewhat hard' to 'hard' (RPE = 13-15) by both groups. The relationship between RPE and %VO2max was altered by training, with trained subjects having a lower RPE at a given %VO2max. It is concluded that RPE at the ventilatory threshold is not affected by training, despite that after training the ventilatory threshold occurs at a higher work rate and is associated with higher absolute and relative metabolic and cardiorespiratory demands.     

Effect of maternal weight gain during pregnancy on exercise performance

We examined the effect of maternal weight gain during pregnancy on exercise performance. Ten women performed submaximal cycle (up to 60 W) and treadmill (4 km/h, up to 10% grade) exercise tests at 34 +/- 1.5 (SD) wk gestation and 7.6 +/- 1.7 wk postpartum. Postpartum subjects wearing weighted belts designed to equal their body weight during the antepartum tests performed two additional treadmill tests. Absolute O2 uptake (VO2) at the same work load was higher during pregnancy than postpartum during cycle (1.04 +/- 0.08 vs. 0.95 +/- 0.09 l/min, P = 0.014), treadmill (1.45 +/- 0.19 vs. 1.27 +/- 0.20 l/min, P = 0.0002), and weighted treadmill (1.45 +/ 0.19 vs. 1.36 +/- 0.20 l/min, P = 0.04) exercise. None of these differences remained, however, when VO2 was expressed per kilogram of body weight. Maximal VO2 (VO2max) estimated from the individual heart rate-VO2 curves was the same during and after pregnancy during cycling (1.96 +/- 0.37 to 1.98 +/- 0.39 l/min), whereas estimated VO2max increased postpartum during treadmill (2.04 +/- 0.38 to 2.21 +/- 0.36 l/min, P = 0.03) and weighted treadmill (2.04 +/- 0.38 to 2.19 +/- 0.38 l/min, P = 0.03) exercise. We conclude that increased body weight during pregnancy compared with the postpartum period accounts for 75% of the increased VO2 during submaximal weight-bearing exertion in pregnancy and contributes to reduced exercise capacity. The postpartum increase in estimated VO2max during weight-bearing exercise is the result of consistently higher antepartum heart rates during all submaximal work loads.     

One repetition maximum prediction models for children using the OMNI RPE Scale

This investigation developed statistical models to estimate one repetition maximum (1 RM) muscular strength using submaximal ratings of perceived exertion (RPE) as predictor variables. Ten- to 14-year-old girls (n = 35) and boys (n = 35) performed two sets (10 repetitions) of biceps curl (BC) and knee extension (KE) exercise using weights approximating 30% and 50% 1 RM. RPE was assessed during the final repetition of each set using the children's OMNI Resistance Exercise Scale (0-10). Sex-specific statistical models predicted 1 RM using RPE derived from both sets of BC and KE exercises. For both girls and boys, RPE ranged from 3.7 to 6.6 for BC and 4.1 to 7.2 for KE. Group mean 1 RM was (a) girls: BC, 7.44 kg, KE, 13.25 kg and (b) boys: BC, 9.19 kg, KE, 16.24 kg. One repetition maximum prediction models for girls were significant (P < 0.01) for BC (r = 0.87) and KE (r = 0.89). One repetition maximum prediction models for boys were significant (P < 0.01) for BC (r = 0.89) and KE (r = 0.87). The RPE predictors were practical and accurate measures, making the 1 RM models potentially applicable when assessing large numbers of children in short time periods.     

Contributions of body fat and effort in the 5K run: age and body weight handicap

The 5K handicap (5KH), designed to eliminate the body weight (BW) and age biases inherent in the 5K run time (RT), yields an adjusted RT (RTadj) that can be compared between runners of different BW and age. As hypothesized in a validation study, however, not all BW bias may be removed, because of the influences of body fatness (BF) and effort (run speed; essentially the inverse as measured by rating of perceived exertion (RPE)). This study's purpose was to determine the effects of BF and RPE on BW bias in the 5KH. For 99 male runners in a regional 5K race (age = 43.9 +/- 12.1 years; BW = 83.4 +/- 12.9 kg), BF was determined via sum of three skinfolds just before the race. RPE, on the 20-point Borg scale, was used to assess overall race effort on race completion. Multiple regression analysis was used to develop a new adjusted RT (NRTadj, the RTadj corrected for BF and RPE), which was computed for each runner and then correlated with BW to determine bias. Indicative of slight bias, BW was correlated with RTadj (r = 0.220, p = 0.029). Both BF (p = 0.00002) and RPE (p = 0.0005) were significant, independent predictors of RTadj. NRTadj was not significantly correlated with BW (r = 0.051, p = 0.61), but BF explained 90%, and RPE explained only 6%, of the remaining BW bias evidenced in the 5KH. The previous finding that the 5KH does not remove all BW bias is apparently accounted for by BF and not RPE. Because no handicap should be awarded for higher BF, this finding suggests that the 5KH, for men, appropriately adjusts for the age and BW vs. RT biases previously noted.     

Energy cost of moderate-duration resistance and aerobic exercise

The purpose of this study was to compare energy expenditure of resistance and aerobic exercise matched for total time and relative intensity. Ten trained men (24.3 +/- 3.8 years) performed 30 minutes of intermittent free-weight squatting at 70% of 1 repetition maximum and continuous cycling at 70% of Vo(2)max, in a crossover design. Vo(2), kilocalories (kcal), work, respiratory exchange ratio (RER), V(E), heart rate (HR), and rating of perceived exertion (RPE) data were recorded. Cycling resulted in greater total Vo(2) (87 +/- 3 vs. 53 +/- 3 L, mean +/- SEM), kcal expenditure (441 +/- 17 vs. 269 +/- 13), and work (335 +/- 11 vs. 128 +/- 11 kJ) than squatting did. The mean RER was greater during squatting (1.03 +/- 0.01 vs. 0.94 +/- 0.01), and the V(E) values were greater during cycling (82 +/- 3 vs. 70 +/- 3 L.min(-1)). The HR response was nearly identical between exercise modes (160 +/- 5 vs. 160 +/- 4 bpm), whereas the RPE was greater during squatting (16.96 +/- 0.41 vs. 14.88 +/- 0.42). These data suggest that although lower than similarly matched aerobic exercise, resistance exercise resulted in an energy cost that would meet the recommendations for kcal expenditure as suggested by the American College of Sports Medicine, if performed 4-5 days per week. These findings should be considered by coaches and trainers working with individuals mutually interested in muscular development and weight management, because programs of structured resistance exercise may assist with both.     

Muscle pain perception and sympathetic nerve activity to exercise during opioid modulation

The purpose of this experiment was to examine the effects of the endogenous opioid system on forearm muscle pain and muscle sympathetic nerve activity (MSNA) during dynamic fatiguing exercise. Twelve college-age men (24 +/- 4 yr) performed graded (1-min stages; 30 contractions/min) handgrip to fatigue 1 h after the ingestion of either 60 mg codeine, 50 mg naltrexone, or placebo. Pain (0-10 scale) and exertion (0-10 and 6-20 scales) intensities were measured during the last 15 s of each minute of exercise and every 15 s during recovery. MSNA was measured continuously from the peroneal nerve in the left leg. Pain threshold occurred earlier [1.8 +/- 1, 2. 2 +/- 1, 2.2 +/- 1 J: codeine, naltrexone, and placebo, respectively] and was associated with a lower rating of perceived exertion (RPE) (2.7 +/- 2, 3.6 +/- 2, 3.8 +/- 2: codeine, naltrexone, and placebo, respectively) in the codeine condition compared with either the naltrexone or placebo conditions. There were no main effects (i.e., drugs) or interaction (i.e., drugs x time) for either forearm muscle pain or RPE during exercise [pain: F (2, 22) = 0.69, P = 0.51]. There was no effect of drug on MSNA, heart rate, or blood pressure during baseline, exercise, or recovery. Peak exercise MSNA responses were 21 +/- 1, 21 +/- 2.0, and 21 +/- 2.0 bursts/30 s for codeine, naltrexone, and placebo conditions, respectively. Peak mean arterial pressure responses were 135 +/- 4, 131 +/- 3, and 132 +/- 4 mmHg for codeine, naltrexone, and placebo conditions, respectively. It is concluded that neither 60 mg codeine nor 50 mg naltrexone has an effect on forearm muscle pain, exertion, or MSNA during high- intensity handgrip to fatigue.