For the past decade, there has been a marked increase in the popularity of handcycling as a competitive sport (17) and as a rehabilitation tool (30). Research suggests that handcycling is an effective mode of exercise for improving aerobic physical work capacity in persons with paraplegia during clinical rehabilitation (30). It is evident that in most spinal cord injury (SCI) clinical environments, measurement tools for the assessment of exercise intensity can be obtained using ergometers and metabolic equipment (5,30). However, after the rehabilitation period and during competitive sports of handcycling, the equipment required to obtain measurements of power output (PO) and oxygen uptake for exercise and/or training prescription are usually cost-prohibitive. Moreover, HR, a method widely used in the able-bodied community for monitoring exercise intensity, cannot be used by some SCI participants because of the attenuated HR response due to the impairment of the autonomic nervous system (22). It is therefore important that other methods, such as the use RPE to estimate and regulate exercise intensity, be evaluated in participants with SCI.
In healthy able-bodied, active, and sedentary participants, the RPE (1,2) correlate directly with metabolic demand as measured by oxygen uptake and HR in both passive estimation tasks, where the RPE is given in response to fixed work rates (6,24,26), and active production tasks, where the RPE is used to regulate and control the work rates (8,10,11,15,28,31). In the latter application, it has been demonstrated that distinct exercise intensities, as calibrated by differences in oxygen uptake, PO and HR, can be reliably produced across a range of RPE in adults (3,7,8,10,11,14,15) and young children/adolescents (12,13). It is well established that the higher HR, oxygen uptake, minute ventilation, and blood lactate responses for arm versus leg ergometry results in higher RPE in able-bodied individuals (6,24).
The question as to whether these procedures can be applied with similar success in persons with SCI is debatable because there are unique exercise responses in individuals with SCI, which include/are related to the loss of sympathetic innervation, resulting in disturbed blood redistribution (19). Nevertheless, this form of exercise prescription (i.e., the use of RPE to quantify exercise intensity) for persons with paraplegia has been examined during wheelchair propulsion (18,23). Grange et al. (18) observed that perceived exertion using the Borg category-ratio 10 scale (2) was a useful measure of exercise intensity during a 45-min Square-Wave Endurance Exercise Test performed on a wheelchair ergometer in a supervised clinical setting. Lewis et al. (21) noted equivocal findings in a similar rehabilitation context, where subjects with paraplegia underestimated their level of exertion at moderate levels of exertion during arm exercise (21). Another work in a sporting environment has found that RPE is fairly reproducible, particularly when the wheelchair propulsive exercise bouts involve high-intensity effort (23). This is encouraging because the use of RPE could enable trained paraplegic participants to have an awareness of the intensity range. This has particular importance for those participants who are physically active and wish to further augment their physical capacity through vigorous exercise (∼70% of V˙O2peak) (27). On the other hand, it perhaps still remains unclear whether RPE can be used at moderate exercise intensities (∼50 of V˙O2peak). Yet, if deemed suitable, this exercise intensity, combined with an appropriate frequency and duration, will be sufficient to enhance the quality of life after the SCI (19). The question therefore remains as to whether the RPE can be used by an individual with SCI to self-regulate exercise. Yet, it has been suggested that several trials with the Borg 6-20 scale are needed for each individual to determine the effective training intensities of participants with SCI (19,23).
Therefore, the purpose of this study was to examine the validity of perception-based intensity regulation (RPE) during a handcycling exercise of 20 min. Specifically, the purpose was to compare the RPE response to an imposed PO equating to moderate and vigorous exercise intensities against an effort production trial where participants regulated PO with the corresponding RPE. A secondary objective was to identify whether sustained changes in PO occurred during the 20-min period when using the RPE to regulate the exercise bouts.
Eight male, wheelchair-dependent participants with SCI at the T4 level or below voluntarily consented to participate in the study. All procedures had been approved by the university's ethics committee. The participants' characteristics and disability classifications are presented in Table 1.
All tests were conducted in an adjustable 18-gear recumbent sports hand bike (Low Rider; Draft, Godmanchester, UK) mounted on a cycle force magnetic flow ergotrainer (T1682; Tacx, Wassenaar, the Netherlands). The cranks were set for the synchronous mode of cranking preferred by all participants. Participants positioned themselves to ensure that the elbow remained in slight flexion at the point furthest from the body during cranking in accordance to previous research (17). Before testing, a deceleration test was performed as described in the operating manual of Tacx. For the fixed PO exercise bouts, the computer program controlled the resistance on the roller via the magnetic brake system so that, in the chosen gear and at a given pedal rate, the required PO was achieved. In this mode, when the pedaling rate changed, the computer immediately adjusted the resistance on the roller; this mode was not used in the RPE-regulated trial. Each participant self-selected a comfortable gear during the 5-min warm-up period. This gear and seat configuration remained the same for each individual for sessions 1 and 2.
Participants visited the laboratory on two separate occasions, separated by at least 5 d but no longer than 7 d. During the first visit to the laboratory, participants completed an incremental test and a V˙O2peak test on the hand bike. Subsequently, two 20-min exercise tests were completed at an individualized PO (50% and 70% of V˙O2peak). This test day was divided into two distinct sessions, separated by a 2-h rest period, to allow a full recovery. On a separate occasion, participants were instructed to produce and maintain for 20 min a workload equivalent to the RPE previously recorded. The imposed PO- and RPE-regulated sessions were performed on separate days always in this order, with the variations in exercise intensity presented in a counterbalanced order.
To familiarize participants of the handcycling configuration and to establish participants' individual PO at both moderate and vigorous exercise intensities (50% and 70% V˙O2peak), an incremental test and a peak oxygen uptake (V˙O2peak) test were performed. Each participant completed an incremental submaximal exercise test comprising of five or six 4-min stages. The initial PO was predetermined after a self-selected warm-up period of 5 min where HR was approximately 100 bpm. Subsequently, each exercise stage was a 10-W increment of the previous stage; this ensured that we obtained a profile that included 50% to 70% V˙O2peak. During the last minute of each stage, expired air was collected and analyzed using the Douglas bag technique. The concentration of oxygen and carbon dioxide in the expired air samples was determined using a paramagnetic oxygen analyzer (Series 1400; Servomex Ltd, Sussex, UK) and an infrared carbon dioxide analyzer (Series 1400; Servomex Ltd). Expired air volumes were measured using a dry gas meter (Harvard Apparatus, Kent, UK) and corrected to standard temperature and pressure (dry). Oxygen uptake (V˙O2), carbon dioxide output, expired minute ventilation, and RER were calculated. HR was monitored continuously using radio telemetry (Sports Tester PE4000; Polar, Kempele, Finland). A small capillary blood sample was obtained from the earlobe at the start of the test and during a 1-min break between stages for the determination of whole blood lactate concentration [BLa−] using a YSI 1500 SPORT Lactate Analyzer (YSI, Inc, Yellow Springs, OH), which had been calibrated with a lactate standard of 5 mmol·s−1 before testing. RPE was monitored throughout the test (2).
After a 15-min rest period, an incremental PO test was used to determine the peak oxygen uptake (V˙O2peak). This test involved increases in external workloads of 10 W every 1 min from an initial mean ± SD PO of 130 ± 40 W at a freely chosen pedal rate. HR was monitored continuously, expired air samples were collected during the last two consecutive stages of the test, and the final RPE was recorded as previously described. The criteria for a valid V˙O2peak were RERpeak ≥ 1.10 and HRpeak ≥ 95% of the age-predicted maximum (200 bpm minus chronological age in years 22). All of the participants satisfied both criteria.
Session 2: imposed power.
For each participant, a linear regression analysis was conducted using the paired data of V˙O2 and HR values. Using the individual linear regressions of V˙O2, PO data and the PO corresponding to 50% and 70% V˙O2peak were determined for each of the participants. Participants were informed of these PO values and were asked to maintain a constant PO for 20 min as two separate trials with a 30-min recovery between the two intensity conditions. Throughout the entire period of exercise, participants had full vision of the PO display.
Session 3: RPE-regulated.
Before the two RPE-regulated trials, participants were informed of the RPE that was recorded at the two previous intensity conditions and that it was their responsibility to adhere to this RPE throughout the 20-min exercise session. After a 5-min low-intensity warm-up, the participant established the target intensity on the basis of the recorded RPE from session 2 by adjusting their gears and pedal rate accordingly. The participant was unable to read the PO display but was informed of the time elapsed.
To obtain a full perspective of the objective and subjective responses to each 20-min trial, V˙O2 and [BLa−] were measured every 10 min, while HR and PO were measured throughout the exercise at 1-min intervals. During the imposed PO trial, participants recalled the RPE at 5-min intervals throughout each trial, and for the RPE-regulated trial, participants were reminded of the target RPE at 5-min intervals.
Each participant received detailed instructions about the use of the 15-point Borg scale, which is a categorical scale of 6-20 (2), and was given examples of how he might rate overall RPE. At the time points described earlier, the RPE scale was presented to the participant who was asked to state the number that reflected the "overall" RPE to integrate central and peripheral sensations of effort.
Data were analyzed using the Statistical Package for Social Sciences (SPSS for Windows Version 16.0; SPSS, Inc, Chicago, IL). Standard descriptives (mean ± SD) were used to characterize the sample for the physical and physiological measures shown in Tables 1 and 2. Normal distribution of the outcome variables was confirmed by Shapiro-Wilk test (W (8) = 0.87-0.98, P = 0.14-0.96). Paired values for V˙O2, percent V˙O2peak, HR, percent HRpeak, and [BLa−] averaged during each 20-min exercise period between the imposed and RPE-regulated trials within each intensity condition were examined using Student's dependent t-tests. Separate 2 × 2 (intensity × trial) within-measures ANOVA were also used to examine a potential interaction between exercise intensity (moderate and vigorous) and trial (imposed and RPE-regulated) using the variables described averaged during each 20-min handcycling exercise period. Minute-by-minute PO data were available, so a 2 × 20 (trial × time) within-measures ANOVA was used to examine this variable separately in the two intensity conditions. Significance was accepted at P ≤ 0.05, and the 95% confidence intervals of the differences (95% CIdiff) are also provided.
Table 1 presents the participants' characteristics and relevant disability descriptions. It can be seen that the minimum experience of manual daily wheelchair propulsion was 3 yr. The majority (6/8) participants had acquired a complete lesion at T4-T10; the two participants with incomplete lesions had greater functional capacity with lesion levels of T9 and T11. Handcycling experience was varied yet not extensive in either total years or frequency of training. The peak physiological responses and POpeak measured are shown in Table 2. V˙O2peak values ranged from 1.86 to 3.23 L·min−1 across all participants with an average POpeak of 165 ± 47 W. It can be seen that all participants met the criteria for a valid V˙O2peak as described in the Methods section.
A comparison of the physiological responses across the trials and conditions is shown in Table 3. None of the between-trial differences in V˙O2, percent V˙O2peak, HR, percent HRpeak, or [BLa−] at either intensity were statistically significant (Table 3). However, some relatively wide 95% CIdiff suggest considerable intraindividual variability when comparing the imposed and RPE-regulated trials. The PO tended be higher in the RPE-regulated than in the imposed trial in the vigorous condition (P = 0.07, 95% CIdiff = −1 to 19 W). In contrast, average HR (absolute and percent peak) for the group across the trials in the vigorous condition was identical (Table 3).
As anticipated, significant main effects for intensity (F (1,7) ≥ 32.0, P ≤ 0.001) for V˙O2, percent V˙O2peak, HR, percent HRpeak, and [BLa−] showed that this manipulation was successful. Nonsignificant trial-by-intensity interactions, again for dependent variables given above, showed that any fluctuations in the outcome variables between the trials were consistent across intensity (F (1,7) ≤ 1.2, P ≥ 0.32).
The trial-by-time interaction was significant for the minute-by-minute PO data at the moderate-intensity exercise (F (19,133) = 1.7, P = 0.04) but not at the vigorous-intensity exercise (F (19,133) = 1.0, P = 0.48; Fig. 1). From 8 min onward, the PO gradually increased in the moderate RPE-regulated trial, whereas a similar "end spurt" was only evident from 17 min in the vigorous RPE-regulated trial. At both intensities, PO was, on average, ∼7% higher in the RPE-regulated trials, although there was considerable intraindividual variability at both intensities, which may have influenced the statistical analyses.
The physiological effects of an SCI can affect the ability of a participant to self-monitor the intensity of exercise (21). However, the results obtained from a group of participants with SCI (T11 incomplete to T4 complete lesions) demonstrated encouraging support for the use of RPE as an effective tool in establishing the moderate and vigorous exercise intensities corresponding to ∼50% and ∼70% of V˙O2peak during handcycling exercise. These findings are not in agreement with the findings of Lewis et al. (21), which, in our view, may be because of the increased fitness status of our sample. The group's mean ± SD HRpeak of 191 ± 8 bpm was comparable to those of able-bodied runners at exhaustion (25). Importantly, it is notable that all participants met the HRpeak of age-predicted maximum (200 bpm minus chronological age), suggesting that HR was not impaired by abnormal autonomic cardiac regulation secondary to the nature of the disability (20). Furthermore, the mean V˙O2peak value of 2.62 L·min−1 provides further confirmation that these participants were well conditioned (16,20).
The present study found that RPE (12 ± 1 and 16 ± 1) elicited from fixed-load work rates at 50% and 70% of V˙O2peak, which corresponded to 72% ± 12% and 87% ± 7% HRpeak, respectively, could be used to produce similar moderate and vigorous intensities, respectively. It would be of interest to verify the use of RPE at lower-intensity training sessions for recovery-based sessions. Interestingly, whereas Müller et al. (23) support the fact that subjective intensity ratings can be used at high-intensity bouts of exercise in wheelchair users (≥80% HRpeak), their observations on the efficacy of completing 1500 m on the basis of a subjective intensity of 1-5 (warm-up pace through to race intensity) only partly support our findings. Using exercise bouts lasting 9 to 4 min, because 5 × 1500-m bouts that were completed at slow to race paces, they observed that, at exercise intensities set at 1-2 (i.e., estimated as ≤80% HRpeak), there was up to a 14.4% variance in RPE during the two occasions. Therefore, further work at the lower end of the exercise spectrum is warranted because the present study represented a range of only 72% ± 12% to 87% ± 7% HRpeak.
We acknowledge that inferences from the results of this study should take into account the fact that that both the incremental exercise test used to determine the maximal functional capacity and the work rate equating to 50% and 70% V˙O2peak and the fixed-load exercise trial at these intensities preceded the RPE-regulated trials. It is therefore likely that the ability of the subject to regulate intensity from the RPE was facilitated by these previous sessions. The extent of this effect is unknown because we do not know how well persons with SCI who do not have a previous exposure to fixed-load-regulated trials can self-regulate via the RPE to meet percent HR and percent V˙O2peak criteria of moderate and vigorous exercises. This remains a limitation of the present study.
It is encouraging to note that, as shown in Figure 1, PO in the RPE-regulated condition was similar to the PO elicited at the same RPE in the imposed condition. It is also interesting to note that in the RPE-regulated trial, PO increased slightly across time in the moderate condition (50% V˙O2peak) and remained the same in the vigorous condition (70% V˙O2peak). This may be considered somewhat surprising because previous research, which has used an "RPE-clamp" model to control exercise intensity in able-bodied individuals, whereby the exercise work rate is free to vary but the exerciser is instructed to maintain the conscious sensation of exertion at a fixed, predetermined level, has observed a decrease in work rate across time (28). In the latter study, where the work rate on a cycle ergometer was clamped at an RPE of 16 (as in the current study), although the decrease in PO was greater in the hot (35°C) versus the normal (25°C) and cool (15°C) conditions, the decrease occurred in all three conditions. These differences were apparent within the initial 20 min of the task. It is important to note, however, that a difference between the two studies is the open- and closed-loop nature of the task. In the study by Tucker et al. (28), the participants were instructed to cycle for as long as possible. There was no set time, and the trial was terminated when the PO reached a point that was 70% of the PO at the start of the trial. In the current study, participants were instructed to exercise for a known period of 20 min, and they were aware throughout the trial of the time elapsed. In this way, knowledge of the end point was explicit, and participants in the current study could therefore anticipate when this was going to happen. This knowledge is considered to be a crucial factor for setting the RPE and may explain the reason for the difference in response between the two studies and the apparent "end spurt" in PO (see (29) for a discussion of these points). Conversely, research has also shown that where PO is fixed at a constant rate during trials and the participant is instructed to exercise until volitional exhaustion (i.e., the task is open loop), the RPE increases accordingly to maximal or near-maximal levels (4,9).
In accordance with the recommendation that the use of daily training on the basis of HR is not encouraged for all persons with an SCI (23), the current study has shown encouraging potential for the use of RPE to self-regulate exercise intensity in persons with lesions at or above T4. However, the conclusions derived from this study must be interpreted with caution because levels of fitness and the level and completeness of injury would need to be considered. This group consisted of relatively well-trained participants, who, when compared with individuals with tetraplegia, are likely to show more sympathetic nerve activity and some stimulation of the sympathetic nervous system during maximal exercise (19). Hence, the validation of these findings in individuals with tetraplegia who have sustained greater sensorimotor loss and subsequent functional and mobility impairment than individuals within the current study is still warranted. The effect of exercise duration is a potential avenue for enquiry to extend the recent aforementioned work in this area to special populations. In addition, the extension of the experimental design to incorporate exercise modes such as wheelchair propulsion would be of interest to both clinicians and sports trainers for exercise and training prescription.
No direct funding was received for this work other than the support from the corresponding institution.
The authors thank the subjects for their time and travel to participate. The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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