Over the last 50 years, a considerable amount of research has been conducted into the development of a ratio scale for evaluating perceived exertion during exercise. The 15-point scale developed by Borg (3) has received the greatest attention in various forms of exercise and across a variety of populations. Although the scale was developed to additionally provide an indication of heart rate, the association between perception of effort and exercise intensity follows an exponential pattern, the mechanisms of which involve the complex integration of various central and peripheral signals (4). Although the relative importance of those central and peripheral components of perceived exertion remain largely elusive, if those perceptions can be used reliably to indicate the physical strain associated with exercise, then it is possible that those same signals could also be used to evaluate recovery after exercise. If so, perceived recovery could be an invaluable tool for regulating interval training where the magnitude of recovery between work bouts determines the overall training stimulus and the subsequent adaptive responses.
Although the evaluation of perceptual responses during short-term postexercise recovery has already received some attention (1,20,24,32), the evaluation of those perceptions has been determined using perceived exertion scales designed to evaluate perceptions of effort during exercise. Moreover, none of the aforementioned investigations linked perceptual responses to the recovery of exercise performance. The aims of this study were therefore (a) to evaluate the pattern of perceived recovery and to compare perceived recovery with the recovery of power output and (b) to compare the pattern of perceived recovery with those of several physiological variables that have been implicated as potential mediating factors in perceptual responses (13).
Experimental Approach to the Problem
During the 10-week period of investigation, the participants completed 10 physiological trials, at approximately the same time of the day, with an average of 7 ± 4 days between each. All the trials were completed in an air-conditioned laboratory maintained at a constant temperature of 18° C. The participants were instructed to maintain their normal diet throughout the testing period, to avoid food and drink in the hour before testing, and to avoid strenuous exercise 24 hours before each trial. Trial 1 was a baseline trial to establish peak power output over 5 seconds and to familiarize the participants with the equipment and the demands of a 30-second maximal cycle sprint test. Trials 2–7 involved the participants performing a 30-second maximal sprint followed by a predetermined stationary rest period and a subsequent 5-second sprint to determine the recovery of peak power output. Trials 8 and 9 were used to establish individual perceptions of recovery after a 30-second maximal sprint and the extent to which individuals had recovered when they perceived they were fully recovered. Trial 10 involved the evaluation of various physiological variables during recovery from a 30-second sprint in an attempt to explain individual perceptions of recovery. Trials 2–7 were randomized, with trials 8 and 9 included in the randomization process after the participants had experienced 2 of the experimental trials. In effect, it was felt important for participants to experience the test before evaluating perceptions of recovery. Trial 10 was the final trial of the investigation.
Seventeen well-trained male strength and conditioning and sport science students volunteered for the study, which was approved by St. Mary's University College Ethics Committee. Before testing, the participants received written and verbal instructions regarding the nature of the investigation and completed a training history questionnaire, which indicated that all had been actively involved in sport for approximately 14 years. Times spent training and competing each week were reported as 8.8 ± 4.9 and 5.0 ± 3.8 hours, respectively. Before the commencement of the study, all the participants completed a health-screening questionnaire and provided written informed consent. Mean ± SD values for age, height, body mass, and estimated body fat (8) of the participants were 22 ± 4 years, 1.83 ± 0.05 m, 78.9 ± 7.6 kg, and 11.1 ± 2.2%, respectively.
All the sprints were performed on an electromagnetically braked cycle ergometer (Lode Excalibur Sport, Groningen, Holland), which was fitted with standard pedals, toe clips, and straps and interfaced with a computer to enable high-frequency logging of the flywheel angular velocity. Perceptions of recovery were recorded using a 20-cm visual analog scale (VAS) ranging from ‘not at all recovered’ to ‘completely recovered.’ Core temperature was monitored using a tympanic thermistor probe (Model CD, Edale Instruments [Cambridge] Ltd., Longstanton, United Kingdom). Blood lactate was evaluated from capillary puncture using an automated analyzer (Biosen C-Line, EKF Diagnostic, Ebendorfer Chaussee 3, Germany). The analyzer was calibrated before all the trials in accordance with the manufacturer's instructions. Heart rates were monitored at 5-second intervals using heart rate monitors (Polar S610, Polar Electro Oy, Kempele, Finland). All respiratory measures were made from expired air (breath-by-breath) using an online gas analyzer (Jaeger Oxycon Pro, Hoechberg, Germany). The analyzer was calibrated before each test using oxygen and carbon dioxide gases of known concentrations (Cryoservice, Worcester, United Kingdom), and the flowmeter was calibrated using a 3-L syringe (Viasys Healthcare GmbH). During the tests, the participants breathed room air through a face mask (Hans Rudolph, Kansas City, MO, USA) that was secured in place by a head-cap assembly (Hans Rudolph).
On arrival at the laboratory, height, body mass, and estimated body fat (determined from the sum of 4 skinfolds) were recorded for each subject. The participants then performed a 4-minute warm-up on the cycle ergometer at a power output of 100 W. The same warm-up procedure was used for all the trials. The saddle height and handlebar position for each subject were determined before the first trial and remained constant for all subsequent trials. On completion of the warm-up and starting from a stationary position, the participants performed a series of 3 × 5-second maximal cycle sprints interspersed with 3-minute stationary rest periods to determine individual measures of peak power output. A torque factor of 0.7 N·m·kg−1 was used for all sprint trials, and the participants were verbally encouraged to give maximal effort. On completion of the third sprint, the participants cycled for a further 3 minutes at a power output of 100 W before performing a 30-second maximal cycle sprint for familiarization purposes. After all the trials, the participants completed a cool-down by cycling at 100 W for a minimum of 5 minutes.
After the warm-up, and from a rolling starting power output of 100 W, the participants completed a 30-second maximal sprint. On completion of the sprint, the participants were instructed to remain stationary on the ergometer for a period of between 5 and 160 seconds before performing a 5-second maximal sprint. Information on the duration of the recovery period was withheld from the subject in every trial, and the computer screen was obscured from view. Because it was anticipated that the recovery of peak power output would likely follow a biphasic pattern (2), the following recovery periods were used: 5, 10, 20, 40, 80, and 160 seconds.
Trials 8 and 9
In trials 8 and 9, the participants followed the same procedure as in trials 2–7 up to the point at which they completed the 30-second sprint. In trial 8, on completion of the 30-second sprint, the participants remained stationary on the ergometer and were asked to indicate, by placing a mark on the VAS at the same time points used for trials 2–7, the extent to which they felt they had recovered their ability to perform a subsequent 5-second sprint. To prevent visual feedback from influencing the results, a fresh VAS was used for each time point in the recovery process. In addition, the participants were asked to indicate at what point in the recovery process they felt they had fully recovered. In trial 9, the participants completed the same procedure as in trial 8, with the additional element of performing a maximal 5-second sprint at the time point in recovery at which they had previously indicated that they felt they had fully recovered.
In trial 10, after the fitting of the face mask and headgear, the tympanic thermistor, and the heart rate monitor, the participants were asked to remain stationary on the ergometer for a period of 3 minutes to enable baseline physiological measurements to be recorded. After a further 4-minute warm-up period, the participants performed a 30-second maximal sprint followed by a 5-minute recovery period during which the following physiological measurements were recorded: heart rate, blood lactate, core temperature, oxygen uptake (V[Combining Dot Above]O2) minute ventilation (VE), and breathing frequency. Blood lactate and core temperature measurements were made at 40-second intervals during the recovery period.
All statistical analyses were conducted using the Statistical Package for the Social Sciences (SPSS for Windows, SPSS Inc., Chicago, IL, USA). Measures of centrality and spread are presented as mean ± SD. The possibility of learning or training effects influencing the outcome of the experiment was evaluated by conducting a 1-way analysis of variance (ANOVA) on peak and mean power output in the 30-second sprints, in trial order. Synchronization of the gas analysis data between the participants was achieved using linear interpolation at 5-second intervals throughout recovery after eliminating values that were outside 4SDs of the midpoint of a rolling 20 breath mean (attributed to ‘noise’) (25). Differences in perceptions of recovery between trials 8 and 9 were evaluated using a 2-way ANOVA, with mean values from each time point subsequently used to investigate the pattern of the recovery process. The recovery data from all the physiological variables were converted to percentages, with values at the end of the 30-second sprint used as the reference point for zero recovery, and with mean resting values from the start of trial 10 used as the reference for full recovery. The recovery of peak power was also determined as percentage data, with peak power from the 5-second sprints in trial 1 considered as the reference for full recovery. Differences between perceptions of full recovery and the recovery of power output at the same time point were evaluated using a Wilcoxon matched-pair test. Differences between perceived recovery and both power output and physiological recovery were evaluated using 2-way ANOVA tests with repeated measures on both factors. The α was set at 0.05 for all analyses. Significant effects were followed up using Bonferroni-adjusted post hoc analyses. Nonsignificant effects were followed up by applying monoexponential models to characterize the kinetics of the corresponding recovery response for each individual using a nonlinear least-squares fitting procedure (XLfit, IDBS Ltd., Guildford, United Kingdom). Models were developed using the same approach previously used for off-transient phosphocreatine (PCr) and V[Combining Dot Above]O2 recovery kinetics (25): ΔX(t) = X0 + ΔX(ss)(1 − e(−t/τ)), where X is the physiological variable concerned, t is the time, ΔX(ss) is the asymptotic value to which X projects, and τ is the time constant of the response (note: because in all the cases, recovery at time point zero was zero, the first term on the right-hand side of the equation was redundant). Resultant time constants were subsequently compared using Pearson correlations.
There was no significant effect of trial order on values of peak (F(4.34,69.51) = 1.572, p = 0.187) or mean (F(8,128) = 1.453, p = 0.181) power output in the 30-second sprints (grand means: 960 ± 146 and 729 ± 86 W, respectively).
Perceived Recovery Vs. the Recovery of Power Output
There were no significant differences between trials 8 and 9 on perceptions of recovery after the 30-second sprint (F(1,16) = 4.350, p = 0.056). The patterns of perceived recovery and the recovery of power output, including the results of the post hoc analysis, are presented in Figure 1. The time in recovery at which individuals perceived they had fully recovered was 163.3 ± 57.5 seconds, at which point, power output was 83.6 ± 5.2% of peak power. In effect, individuals significantly (p < 0.001) underestimated full recovery by 16.4% (95% likely range: 13.7–19.0%). Analysis of the data revealed a significant effect of variable (F(1,16) = 16.99, p < 0.001), time (F(2.5,40.3) = 299.75, p < 0.001), and variable × time (F(2.7,42.8) = 11.68, p < 0.001).
Perceived Vs. Cardiopulmonary Recovery
The recovery patterns of the various cardiopulmonary factors are presented in Figure 2, with patterns of actual recovery presented in Figure 3. There was a significant effect of time (p < 0.001) on each variable. There were also significant variable × time interactions for V[Combining Dot Above]O2 (F(3.07,49.19) = 4.55, p = 0.006), VE (F(5,80) = 20.24, p < 0.001), breathing frequency (F(2.21,35.32) = 56.43, p < 0.001), and heart rate (F(2.27,36.32) = 17.539, p < 0.001). Significant differences between variables were only observed in analyses involving breathing frequency (F(1,16) = 120.90, p < 0.001) and heart rate (F(1,16) = 50.14, p < 0.001). Moreover, post hoc analyses were only able to detect differences in contrasts involving breathing frequency and heart rate. Time constants for perceived recovery, V[Combining Dot Above]O2, and VE were 86.2 ± 33.2, 54.6 ± 15.8, and 92.3 ± 36.3 seconds, respectively. Correlations between the time constants of perceived recovery and both V[Combining Dot Above]O2 and VE were −0.07 (95% likely range: −0.53–0.43) and 0.23 (95% likely range: −0.28–0.64), respectively.
Perceived Vs. Peripheral Recovery
The patterns of perceived recovery vs. the recovery patterns of blood lactate and core temperature are presented in Figure 4, with actual blood lactate and core temperature responses presented in Figure 5. The analysis revealed significant differences between the process of perceived recovery and those of blood lactate (F(1,16) = 14.22, p = 0.002) and core temperature (F(1,16) = 121.74, p < 0.001). There was a significant effect of time for perceptual responses and core temperature in recovery (F(1.49,23.76) = 15.91, p < 0.001). Significant interactions were observed between the patterns of perceived recovery and those of blood lactate (F(1.01,16.21) = 13.81, p = 0.002), and core temperature (F(2,32) = 12.44, p < 0.001). Post hoc analyses revealed significant differences between all contrasts (Figure 4).
The aims of this study were to evaluate postexercise perceptions of recovery and to compare the pattern of those perceptions with the recovery patterns of several potential mediating physiological variables. The results revealed significant differences between the patterns of perceived recovery and the recovery of peak power output. In effect, individuals significantly underestimated recovery in the early stages of the process, with the 2 patterns converging as time progressed. Nevertheless, the results revealed a relatively small (given the absence of any external reference of elapsed time) but significant underestimation of the time to full recovery. In a recent investigation, it was established that individuals were able to maintain performance in a multiple sprint test (12 × 30 m) when left to choose their own between-sprint recovery durations (12). Moreover, after the completion of the first 2 sprints, the duration of those self-selected recovery periods was not significantly different within individuals. Although the underestimation of full recovery in this study appears to conflict with these findings, the 30-second sprint in this study was designed to largely deplete PCr stores (33). In contrast, the 5-second sprints used by Glaister et al. (12) would only partially reduce PCr stores and as such, any slight underestimation of full recovery would be unlikely to affect peak power output, at least in the early stages of the protocol. Indeed, the idea of a slight underestimation of full recovery in the Glaister et al. (12) investigation may explain why the duration of perceived recovery was adjusted (lengthened) by the participants after the completion of the first 2 sprints.
The pattern of perceived recovery was similar to that observed in studies that have investigated perceptual responses during recovery using perceived exertion scales (1,20,32). Although Robertson et al. (24) noted a more linear response, the authors also found a similar nonlinear pattern when perceptual responses were constrained to feelings of strain associated with ventilatory effort. Although it is difficult to say whether perceptions of recovery are the same as those derived using perceived exertion scales, the similarities between the 2 processes combined with the fact that ratings of perceived exertion do not return to baseline immediately upon cessation of exercise suggests that they may be.
Despite the absence of any significant differences between the recovery kinetics of perceptual responses and those of V[Combining Dot Above]O2 and VE the time constants of the corresponding monoexponential recovery kinetics were poorly correlated. Moreover, although post hoc tests were unable to detect any significant differences, the results suggest that time affected the degree of similarity between perceptual and both V[Combining Dot Above]O2 and VE kinetics. Previous research into the relationship between perceptual responses during recovery and V[Combining Dot Above]O2 has shown that, despite similarities in recovery patterns, the 2 processes appear to be unrelated because their kinetics become dissociated under conditions of induced alkalosis (32) and hyperoxia (1). Indeed, research into the link between V[Combining Dot Above]O2 and perceptual responses during exercise suggests that, despite evidence of a positive relationship (r = 0.76–0.97), particularly when V[Combining Dot Above]O2 is expressed as a percentage of V[Combining Dot Above]O2max (27,28), V[Combining Dot Above]O2 is unlikely to directly influence perceptual responses because its kinetics cannot, it appears, be consciously monitored (18). In contrast, VE which has also been shown to strongly correlate (r = 0.61–0.94) with perceived exertion during high (greater than ∼70% V[Combining Dot Above]O2max) (23), rather than low-intensity exercise (6,9) and, in some instances, with perceptions of strain in recovery (24,32), may well explain recovery perceptions. Previous research comparing perceptions of exercise intensity with VE has suggested that the strong correlation between the 2 variables at high exercise intensities is because of afferent feedback from mechanoreceptors associated with the recruitment of ancillary muscles of respiration (23). Because these same muscles remain highly activated during the early stages of recovery, the same process may also explain the link between VE and perceived recovery. Moreover, the reduced activation of the aforementioned ancillary muscles as recovery progresses may explain the nonsignificant widening gap between VE and perceptual responses over time and as such explain the variable × time interaction. However, if VE can explain perceptual responses, aside from a possible homogeneity effect and a limited number of data points with which to model the perceptual responses, it is difficult to reason out why their respective time constants were poorly correlated.
Although the link between perceptual responses and VE appears to hold for both exercise and recovery, the same does not appear to be true for breathing frequency. Previous research examining the relationship between perceptual responses and respiratory variables during exercise has reported similar correlations between perceptions of exertion and breathing frequency as those reported for perceptual responses and VE (16,21,22). Conversely, although similar patterns of breathing frequency and VE have been observed in recovery after exercise (1,24,32), none of the studies observed a significant relationship between perceptual responses and breathing frequency. However, previous research into perceptual responses during recovery used end-exercise intensities ≤V[Combining Dot Above]O2max as the starting point for recovery. In contrast, this study used a much higher exercise intensity to provide a more complete description of the recovery process. As a result, the rapid decline in breathing frequency in the early stages of recovery, in comparison with the much steadier decline in VE shows a clear disparity between the kinetics of the 2 processes.
It is difficult to say whether the cues involved in perceptions of recovery are different from those used in perceptions of effort, although the results from the breathing frequency and heart rate data suggest that this may be the case. However, the relationship between heart rate and perceived exertion during exercise is far from as certain as the original work by Borg (3) and subsequent others (27,28,30) have suggested. For instance, the association between heart rate and perceived exertion has been shown to break down as a result of various environmental and pharmacological interventions (7,10,16,22). In effect, because the relationships between perceptions of effort and both breathing frequency and heart rate are far from clearly established, the perceptual cues that determine the extent of recovery could very well be the same as those used to determine levels of exertion.
The disparity between the recovery kinetics of perceptual responses compared with those of blood lactate, contrasts with the large number of studies which support a significant positive relationship (r = 0.61–0.77) between perceived effort and blood lactate during both exercise (9,11,19) and recovery (1,24,32). However, the lower exercise intensities used, coupled with the lack of frequent sampling (≤3 samples per investigation), raises concerns regarding the validity of the assumptions drawn in previous recovery-based investigations. Indeed, Swank and Robertson (32) highlight that the single measure of blood lactate obtained 5 minutes into their recovery protocol represents a limitation to their conclusions. Concerns also exist regarding the link between perceived effort and blood lactate during exercise because, as with VE the lack of any appreciable accumulation of blood lactate below lactate threshold means that the relationship only appears to hold true for higher exercise intensities. Once again, although the results of various experimental interventions add support to a blood lactate-perceived effort relationship (1,5,10,11,14,15,32), others report contradictory findings (17,29,31). If the cues for perceptual responses are the same in exercise and recovery, then the results of this study clearly show that blood lactate is not a causal factor. However, the contrast between the above findings may simply be a reflection of the fact that muscle, rather than blood, lactate is the influential cue in the perceptual response. In effect, the increase in blood lactate during the recovery period represents the time lag between production, efflux, diffusion, and sampling. In contrast, because anaerobic glycolysis shuts down on cessation of exercise, the corresponding decline in muscle lactate could be a mediating factor in the perceptual response. Then again, the much slower decline of muscle lactate relative to that of PCr (26,33) suggests that neither muscle nor blood lactate is related to the perceptual response.
Finally, although previous research has suggested a possible influence of core temperature on perceptual responses, it appears that any such influence only occurs under extreme environmental conditions when the ability to defend any rise in core temperature is compromised (16,21). In this study, the absence of any notable change in core temperature during recovery, in contrast to the relatively major changes in perceived recovery, supports the view that core temperature has no influence on perceptual responses under normal (neutral) environmental conditions (13,18).
The results of this study show some disparity between perceptions of recovery and the recovery of power output. Although individuals tended to underestimate recovery in the early stages of the process, the 2 patterns converged as time progressed resulting in an underestimation of the time to full recovery. From a practical perspective, coaches and athletes need to be aware of the above and, depending on the goals of the session, adjust recovery periods accordingly if perceived recovery is to be used to regulate rest intervals during training. In the end, as with perceptions of effort, it is difficult to reconcile the physiological cues that regulate perceptions of recovery. However, if perceptual cues are the same for exercise and recovery then, based on the findings of this study, it is difficult to make a case for influential factors other than V[Combining Dot Above]O2 and VE.
The authors would like to express their gratitude to all the participating subjects for their enthusiasm and commitment to this investigation, and to St. Mary's University College, School of Human Sciences Research Support Fund for funding this research.
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Keywords:Copyright © 2012 by the National Strength & Conditioning Association.
perceived exertion; Wingate; sprinting; power output