The anaerobic threshold has been defined as the theoretical highest exercise level that can be maintained for prolonged period. The knowledge of the anaerobic threshold is an important factor in the field of sport training and performance (15,16) but also in the rehabilitation of people suffering of cardiac disorders (1,11). At the present time, there are various methods to determine the anaerobic threshold. Several studies (2,18,19) have determined the anaerobic threshold from the ventilatory response previously defined by Wassermann et al. (24). This method consists of an incremental exercise test until exhaustion to investigate the ventilatory responses such as minute ventilation (VE), oxygen consumption (O2) or carbon dioxide production (VCO2).
Stegmann et al. (20) developed another method usually employed to predict the endurance performance called individual anaerobic threshold (IAT). IAT represents a metabolic rate where the elimination of lactate (La) from the blood is maximal and equal to the rate of diffusion of La from the exercising muscle to the blood. A lot of studies reported that well-trained athletes could exercise at IAT below one hour conserving individual steady-state blood lactate values (14,21). The reproducibility of this method has been previously reported by McLellan et al. (14). Davis et al. (4) described another method to determine the ventilatory threshold based on the slope of the graphical ventilatory curves.
However, these techniques are not easily usable every day during training or competition. For this reason, Conconi et al. (3) proposed to use heart rate recording to determine the anaerobic threshold. However, Groslambert et al. (7) reported that heart rate may not be a good indicator of exercise intensity at ventilatory threshold (VT) because during a steady state exercise, like cycling time trial, the authors observed that heart rate is influenced by psychological stress and by the mechanisms of thermoregulation. Borg (1) proposed to determine the anaerobic threshold from perceived exertion. The author reported that perceived exertion may be considered as configuration of sensations including strain, aches fatigue involving the muscles and the cardiovascular or pulmonary systems. Feriche et al. (6) and Stojiljkovic et al. (22) reported that a fixed value of 12-13 on the Borg's Rating of Perceived Exertion (RPE) scale (1) might be used to detect the exercise intensity corresponding to the VT. This result is in accordance with Hill et al. (9), who also observed that during the transition of the ventilatory threshold, perceived exertion increased significantly in relation with physiological factors like ventilatory and heart rate, blood lactate accumulation, and oxygen consumption (o2). Lind et al. (13) used the feeling scale (FS) of Hardy and Rejeski (8) to observe that affective valence (AV), which corresponds to pleasure or displeasure felt during physical activity, remained positive and stable before the point of transition to aerobic to anaerobic metabolism.
However, most of the studies that determine perceptively the ventilatory threshold (5,13,22) were carried out on sedentary subjects and investigated perceived exertion by using the Borg's RPE 6-20 (1). One major limit is that this rating scale has been constructed to follow the physiologically linear increase of aerobic energy demands for increasing exercise intensity. For this reason and in agreement with Borg (1), we propose to use in the present study the category ratio (CR)-10 scale by Borg (1). This scale appears to be a more appropriate tool to measure perceived exertion throughout a nonlinear and positively accelerating growth function corresponding to the physiological responses (i.e., blood lactate or blood pH) usually observed during a maximal graded test. Therefore, the aim of this preliminary study was to estimate the ventilatory threshold from perceived exertion by using the CR-10 and the AV in trained cyclist during a maximal exercise test. We hypothesised that the use of these tools will allow us to determine their VT.
Experimental Approach to the Problem
To individualize a cycling training program, most coaches have to determine VT. However, the determination of this threshold requires sophisticated material and is very expensive. For this reason, it may be interesting to validate from perceptual markers a simple method that determines the VT.
Ten apparently healthy trained male cyclists (n = 10) volunteered for this study. Their descriptive characteristics and selected physiological responses at maximal exercise are presented in Table 1. Individuals taking medications including anti-inflammatories, antihistamines, pain medications, or antidepressants were excluded. All participants were involved in a regular physical training and performed in national level cycling competitions. The participants gave their written consent in order to participate to the investigation. The experiments comply with the Helsinki declaration (1983) and the protocol was approved by the local ethics committee. Participants were asked to maintain their normal diet and training for the study. Each participant was familiarized with the testing protocol and equipment, but was not informed about the expected results of this study.
Maximal Graded Test
Each participant came to the laboratory around the same time of the day to avoid a possible influence of circadian hormonal responses on perceived exertion, and performed a maximal graded test on a cycle ergometer Monark (818E, Vaberg, Sweden). They began the test at 120 W, and the exercise intensity was increased by 30 W every 2 minutes. The pedalling cadence was kept constant at 80 rpm. To confirm that o2 max was reached, two of the three following criteria had to be attained: a drop in pedalling cadence below 70 rpm, a respiratory exchange ratio (RER) value exceeding 1.1, and a plateau in o2. o2max and the associated maximal power output (POmax) were defined as the highest mean value over a 30-second period during the last stage of the incremental exercise test. The gas exchange data were collected continuously by using an automated breath-by-breath metabolic cart (CPX, Medical Graphics, St. Paul, Minnesota, USA), which measured the following variables: o2(L·min−1), carbon dioxide production (co2, L·min−1), minute ventilation (e2, L·min−1), ventilatory equivalents for oxygen (e2 /o2), and carbon dioxide (e2/co2). Before and after each exercise, known composition of gases and a 3-l Rudolph syringe were used for calibration of the rapid gas analysers and pneumotachograph, respectively.
Determination of Ventilatory Threshold
For the determination of VT corresponding to the independent variable, the method described by Davis et al. (4) was used. Two criteria were used to discern the subject's VT from the maximal graded test: a) a systematic increase in the ventilatory equivalent for O2 (e2/co2) without an increase in the ventilatory equivalent for CO2 (e2/o2), and b) a systematic increase in end-tidal inspired O2 partial pressure (PET O2) without a decrease in end-tidal expired CO2 partial pressure (PET CO2). For most subjects, both criteria were met, although in few instances the systematic increase in e2/o2 was easier to discern (and therefore weighted more heavily in the decision of the VT magnitude) than the systematic rise in PET O2. Three investigators matched their results to confirm the value of VT. The power output (PO) at VT has been also calculated for each subject.
Evaluation of Perceived Exertion and Affective Valence
Overall perceived exertion was investigated by using the CR-10 scale of Borg (1), which was presented in standardized condition to the participant before the test. The scale for eliciting the different levels of overall perceived exertion is a scale with numbers from 0 (no exercise) to 10 and more (highest exertion possible; Figure 1). Affective valence (positivity-negativity or pleasure-displeasure) was assessed by the FS (8). The FS is an 11-point, single-item, bipolar rating scale commonly used for the assessment of affective responses during exercise. The scale ranges from −5 (very bad) to 0 (neutral) to +5 (very good). In this study, PE and VA were the dependent variables and were measured at the end of each step of the maximal graded test. In order to avoid a possible order effect, the different rating scales were randomly presented to participant at the end of each intensity level.
To compare the data between the subjects, after the identification of the VT, PE, and AV, data collected at the following eight time points during exercise were retained: the first and second minutes (min 1 and 2) after the beginning of the maximal graded test (GXT), 1 minute before the VT (VT-1), at the VT (VT), one minute after the VT (VT+1), two minutes after the VT (VT+2), one minute before the end (End -1), and at the end (End) of the GXT. Data are presented as mean ± SD.
Correlation statistical analyses between PO, PE, and AV were examined during GXT but also at PO corresponding to VT. As the data from the present study met the statistical assumptions for using parametric statistics (i.e., homogeneity of variance and normality of the sample distribution), a one-way analysis of variance (time) and a Fischer post-hoc test were used. Statistical significance was accepted at the p < 0.05 levels. Most of the subjects (7 out of 10) reported PE and AV values corresponding to the PO measured at VT. If these values were not reported, an individual regression analysis was to be conducted to interpolate the missed PE and AV data points. According to Robertson et al. (17), in this interpolation procedure, PE and AV values are expressed as a function of PO by using data from all stages of the GXT. The derived regression equations use the target PO to solve their corresponding PE and AV values for each subject. In addition a correlation analysis (SigmaStat, Jandel Corporation, San Rafael, CA, USA) between PO, PE, and AV has been performed in order to determine possible relationships between these variables.
All participants attained at least two of the three criteria used to confirm the end point of the maximal graded test (Table 1) and that the o2max was reached. The average duration of exercise until point of volitional exhaustion was 17.3 ± 2.66 min. The VT was determined to be at 88.91 ± 5.02% of o2max, with range from 83.07 to 95.23%. There is a significant relationship between PO and PE (p < 0.01; r = 0.97) and AV (p < 0.01; r = 0.94) measured during GXT (Figure 2). The analysis of variance indicated a significant time effect for PE (F = 182.03; p < 0.0001) and AV (F = 42.62; p < 0.0001) during the GXT (Table 2 and Figure 3). Follow up analyses showed a significant difference for PE and AV between VT and Min 1, Min 2, VT+1, VT+2, End -1, and End. However, no significant difference was found for PE and AV between VT and VT-1. At VT, the mean values for PE (PEVT) were 5.85 ± 0.82 and −0.95 ± 1.64 for AV (AVVT). The power outputs corresponding to a CR-10 of 5.85 and an FS of −0.95 has been examined for each individual. Then, the mean PO measured at VT (POVT) was 306 ± 39.5 W. The mean POs corresponding to PEVT and AVVT were 311.6 ± 32.7 W and 293.0 ± 51.2 W, respectively, revealing for PEVT a difference less than 1.8% and less than 5% for AVVT. Significant correlations were found between POVT and PEVT (r = 0.92, p < 0.05) and AVVT (r = 0.72, p < 0.05).
The aim of the present preliminary study was to determine the ventilatory threshold in trained cyclists from perceptual markers (perceived exertion and the affective valence) by using CR-10 and FS during a maximal exercise test. The results of the present study show that all subjects fulfilled the criteria for attaining o2max, a plateau in the o2 with increased workload, RER value >1.1, and pedalling cadence <70 rpm during the GXT. This result confirms that for all participants o2max was reached. The percentage of o2max found at VT (88.91 ± 5.02%) is higher than the results observed in sedentary subjects (77.2 ± 5.0% and 78.2 ± 5.02%) in Ekkekakis et al. (5), but corresponds to the values previously reported in trained cyclists of 82% in Hopkins and McKenzie (10). The significant correlation found between PO and PE (r = 0.97) is in line those previously reported by Borg of r > 0.90 (1).
However, the most important finding of the present study is that at VT, all of the perceptual responses are significantly different compared to the values assessed 1 min after VT. Mean value for perceived exertion (5.85 ± 0.82) corresponds to the item “strong” in the Borg CR-10 scale (1) and is caused by the intense exercise. Although the data were not available, it is probable that an important acidosis and muscular pain may explain these values. Our results are in line with Perrey et al. (15) who used the Borg RPE scale (1). They reported 15.7 ± 0.4 values at VT during a GXT, corresponding also to “heavy” muscular exercise. However, at VT lower RPE values were reported in previous studies that also used the Borg RPE scale (1): 13.1-14.2 in Purvis and Cureton (16), 13.1-14.7 in Hill et al. (9), 12.8 ± 0.5 in Swaine et al.(23), 12-13 in Feriche et al. (6) and Stojiljkovic et al. (22), and 13.15 in Ekkekakis et al. (5). This difference appears unclear and may be caused by the different experimental protocol used to determine the ventilatory threshold and the difference in the fitness level of the subjects tested. The value of affective valence (−0.95 ± 1.64) indicate that at VT, exercise intensity produces a bad feeling. This result is in line with Lee et al. (12), who reported in coronary heart disease patients that high exercise intensity training (85% of o2max) compared to low exercise training (50% of o2max) is associated with reduced pleasure during the activity and with reduced exercise adherence. Therefore, AV may be also an important perceptual marker for athletes who would like to perform a long and pleasant training program.
Finally, the results of the present study provide partial validation evidence for perceptual markers to estimate the PO at the ventilatory threshold compared to the VT method. The significant correlations found between POVT, PEVT, and AVVT confirm this result. In addition, the low difference between POVT compared to PEVT was less than 6 W. This potential error appears acceptable to control exercise intensity during a training session. Concerning AVVT, the difference with POVT was equal to 13 W. This difference is obviously too great in experimental studies but suggests that affective valence measurement may be also a simple and useful method to control exercise intensity during a training session. This result may be investigated in further research. However, several limitations need to be appreciated. First, our participants were relatively unique because they were young male trained adults. Thus, our findings may not be generalized to more aged or younger participants. Likewise, further investigations carried out on a large experimental sample and exploring other exercise mode (e.g., walking, running, swimming) and including a test-retest procedure are encouraged to confirm the results of the present study.
Our results confirm, in the experimental conditions of this preliminary study, that during an exercise performed at an intensity superior to VT, many significant changes of perceptual markers appear. For this reason, perceived exertion and affective valence are perceptual markers that can be used to identify the ventilatory threshold, which would be valuable for individuals to be able to recognize during training or competition. This result may allow cyclists to control exercise intensity, particularly during individual time trials. This preliminary study revealed also that endurance exercise (inferior to the ventilatory threshold) does not afford unpleasant sensations. This finding may be useful for coaches who would like to increase the participation of the athletes in their endurance training programs.
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