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This investigation examined the overall and localized perceived exertion responses to repeated bouts of submaximal, high-intensity running when subjects were deceived. Well-trained male and female (n=40) runners were randomly assigned to four groups who completed three 1680-m bouts of running at 80-86% peak treadmill running speed. The two experimental groups, Expected Similar and Expected Increase, were deceived of the actual run intensities while the two control groups, Control Increase and Control Similar, were informed of the actual protocol. After each run, ratings of perceived exertion (RPE) were taken for the whole body, chest, legs, head, and other areas. No significant differences were found in overall RPE between deceived and control groups. However, there was a tendency for the Expected Increase group, deceived into believing the intensity would be higher than they were subsequently made to run, to experience an attenuated increase in RPE between runs compared to the control group (Control Increase) who were honestly informed. For all groups, legs and chest were given consistently higher localized exertion scores than the head and other areas. It appears that a precise system of afferent feedback mediates the overall perceived exertion response during high-intensity running, and psychological intervention that alters pre-exercise expectations has minimal feedforward effect on exertion ratings taken postexercise.

Purpose: To assess the reliability and stability of 400-m swimming and 1500-m running competitions to establish the number of samples needed to obtain a stable pacing profile. Coaches, athletes, and researchers can use these methods to ensure that sufficient data are collected before training and race strategies are constructed or research conclusions are drawn. Method: Lap times were collected from 5 world and European championship finals between 2005 and 2011, resulting in the capture of data from 40 swimmers and 55 runners. A cumulative mean for each lap was calculated, starting with the most recent data, and the number of races needed for this to stabilize to within 1% was reported. Typical error for each lap was calculated for athletes who had competed in more than 1 final. Results: International swimmers demonstrated more reproducible performances than runners in 3 of the 4 laps of the race (P < .01). Variance in runners’ lap times significantly decreased by 1.7-2.7% after lap 1, whereas variance in swimmers’ lap times tended to increase by 0.1-0.5% after lap 1. To establish a stable profile, at least ten 400-m swimmers and forty-four 1500-m runners must be included. Conclusions: A stable race profile was observed from the analysis of 5 events for 1500-m running and 3 events for 400-m swimming. Researchers and athletes can be more certain about the pacing information collected from 400-m swimming than 1500-m running races, as the swimming data are less variable, despite both events being of similar duration. [ABSTRACT FROM AUTHOR]

Purpose: Exercise is known to result in hemodynamic changes in the bilateral prefrontal cortex. The aim of this study was to investigate hemodynamic changes in right and left hemispheres of the prefrontal cortex (PFC) during incremental cycling exercise. Methods: After 10 min rest, 9 participants (mean age 26.6 ± 2.5 y, mass 77.5 ± 9.7 kg, stature 1.79 ± 0.9 m) cycled a't 100-150 W for 4 min. Thereafter, resistance was increased by 25 W every 4 min until exhaustion (EXH). Respiratory exchange and concentrations of oxy- ([Hb02]), deoxy- ([(HHb]), and total hemoglobin ([Hbtol]) in the PFC were continuously measured. Data were averaged for 60 s at rest and preceding ventilatory threshold 1 (VT1,), VT2, and volitional EXH and after 5 min recovery. Subjective ratings of affect were measured at VT,, VT2, VT, minus 25 W (VT,-25W), and VT2 plus 25 W (VT2+25W). Results: There were no between-hemispheres differences in [Hb02] or [Hbtol] at rest, VT,, or recovery or in [HHb] at any point. Right-hemisphere [Hb02] and [Hbtot] were significantly greater than left at VT2 {P = .01 and P = .02) and EXH (P = .03 and P = .02). Affect was significantly greater at VT1 25W vs VT2 and VT2+25W and at VT, and VT2 vs VT2+25W {P < .01-03). Conclusions: To the authors' knowledge, this is the first study to describe an exercise-state-dependent change in PFC asymmetry during incremental exercise. The asymmetry detected coincided with a decrease in affect scores in agreement with the PFC-asymmetry hypothesis. [ABSTRACT FROM AUTHOR]

The impact of altered blood glucose concentrations on exercise metabolism and performance after a low carbohydrate (CHO) diet was investigated. In random order, 1 wk apart, 9 trained men underwent euglycemic (CI) or placebo (PI) clamps, while performing up to 150 min of cycling at 70% after 48 h on a low CHO diet. The range in improvement in endurance capacity with glucose infusion was large (28 ± 26%, P < 0.05). Fifty-six percent of subjects in CI failed to complete 150 min of exercise despite maintenance of euglycemia, while only 2 subjects in PI completed 150 min of exercise, despite being hypoglycemic. Total CHO oxidation remained similar between trials. Despite longer exercise times in CI, similar amounts of muscle glycogen were used to PI. Maintenance of euglycemia in the CHO-depleted state might have an ergogenic effect, however, the effect is highly variable between individuals and independent of changes in CHO oxidation. [ABSTRACT FROM AUTHOR]

Goedecke, Julia H., Alan St Clair Gibson, Liesl Grobler, Malcolm Collins, Timothy D. Noakes, and Estelle V. Lambert. Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes. Am J Physiol Endocrinol Metab 279: E1325-E1334, 2000.--We examined the variability and determinants of the, respiratory exchange ratio (RER) at rest and during exercise, in 61 trained cyclists. Fasting (10-12 h) RER was measured at rest and during exercise at 25, 50, and 70% of peak power output ([W.sub.peak]), during which blood samples were drawn for [lactate] and [free fatty acid] ([FFA]). Before these measurements, training volume, dietary intake and muscle fiber composition, [substrate], and enzyme activities were determined. There was large interindividual variability in resting: RER (0.718-0.927) that persisted during exercise of increasing intensity. The major determinants of resting RER included muscle glycogen content, training volume, proportion of type 1 fibers, [FFA] and [lactate], and %dietary fat intake. (adjusted [r.sup.2] = 0.59, P [is less than] 0.001). Except for muscle fiber composition, these variables also predicted RER at 25, 50, and 70% [W.sub.peak] to different extents. The key determinant at 25% [W.sub.peak] was blood-borne [substrate], at 50% was muscle, [substrate] and glycolytic enzyme activities, and at 70% was [lactate]. Resting RER was also a significant determinant of RER at 25 (r = 0.60) and 50% (r = 0.44) [W.sub.peak]. muscle enzyme activities; muscle glycogen and triglyceride content; training volume; dietary intake

We investigated cerebral responses, simultaneously with peripheral and ratings of perceived exertion (RPE) responses, during different VO2MAX-matched aerobic exercise modes. Nine cyclists (VO2MAX of 57.5 ± 6.2 ml·kg-1 ·min-1 ) performed a maximal, controlled-pace incremental test (MIT) and a self-paced 4 km time trial (TT4km). Measures of cerebral (COX) and muscular (MOX) oxygenation were assessed throughout the exercises by changes in oxy-(O2Hb) and deoxy-hemoglobin (HHb) concentrations over the prefrontal cortex (PFC) and vastus lateralis (VL) muscle, respectively. Primary motor cortex (PMC) electroencephalography (EEG), VL, and rectus femoris EMG were also assessed throughout the trials, together with power output and cardiopulmonary responses. The RPE was obtained at regular intervals. Similar motor output (EMG and power output) occurred from 70% of the duration in MIT and TT4km, despite the greater motor output, muscle deoxygenation (↓ MOX) and cardiopulmonary responses in TT4km before that point. Regarding cerebral responses, there was a lower COX (↓ O2Hb concentrations in PFC) at 20, 30, 40, 50 and 60%, but greater at 100% of the TT4km duration when compared to MIT. The alpha wave EEG in PMC remained constant throughout the exercise modes, with greater values in TT4km. The RPE was maximal at the endpoint in both exercises, but it increased slower in TT4km than in MIT. Results showed that similar motor output and effort tolerance were attained at the closing stages of different VO2MAX-matched aerobic exercises, although the different disturbance until that point. Regardless of different COX responses during most of the exercises duration, activation in PMC was preserved throughout the exercises, suggesting that these responses may be part of a centrally-coordinated exercise regulation. [ABSTRACT FROM AUTHOR]