Method

PARTICIPANTS

After approval from the Keele University ethics committee, agreement was then reached with the Royal College for the Blind, Hereford, UK (RCB) to recruit participants. A pilot study was first performed with five members of England's blind soccer team to determine the practicalities of the procedures. The study group consisted of 10 healthy registered blind students of the RCB. There were four women (mean (SD) age 22 (7.6) years) and six men (mean (SD) age 27.3 (11.7) years). All were able to read braille to a high standard. Those with partial vision and/or able to detect light but still registered as officially blind wore special shaded glasses during the exercise tests to ensure that all participants performed the exercise under the same completely unsighted conditions.

EQUIPMENT

The braille RPE scale was mounted on to the hard flat surface of the cycle ergometer's console (fig 1). The cycle ergometer (Tectrix Bikemax, Irvine, California, USA) operated on an electromagnetically braked system. Work rate was adjustable to increments of 10 W in the range 10–450 W and independent of pedal speed. The independence of work rate from pedal speed assumed that participants kept within a recommended pedal speed range of 50–80 rpm.²⁹ Furthermore, an “integrated/overall” RPE has also been shown to be independent of pedal speed in the range 50–80 rpm at a given work rate.³⁰ The cycle was fitted with a heart rate receiver linked to a standard two lead wireless chest strap radio transmitter belt (Polar Electro, Oy, Finland). Expired air was measured continuously using a “breath-by-breath” system (MedGraphics CPX/D Cardiopulmonary Exercise System; Medical Graphics, Minneapolis, Minnesota, USA), which used a low resistance pneumotach and Pitot tube flow meter. The system was calibrated before each trial for each participant using a 3 litre syringe for volume across a wide range of flow rates and against known gases for the O₂ and CO₂ analysers.

TESTING PROTOCOL

The following testing protocol was carried out over five days.

Day 1: familiarisation

The participants gathered in two separate groups to be familiarised with the whole testing procedure. A full description of the testing was explained, including the need for maximal effort, and participants then gave preliminary signed informed consent. Each group was then introduced to Borg's 15 point RPE scale¹ in its braille format. Participants sat at a desk and were given the opportunity to read over the RPE scale until they stated that they had a clear understanding of both the numerical and verbal statements making up the scale. They were then taken through the recommended and standardised procedure of administration/familiarisation of the RPE scale,^1,6 including: understanding the definition of RPE; “anchoring” the top and bottom ratings to previously experienced sensations of no exertion at all and extremely hard/maximal exertion; explanation of how the scale works; being made aware of giving an “all-over” integrated rating which incorporates both peripheral muscular and central cardiorespiratory sensations; understanding that there was no right or wrong rating; ensuring that the rating represented how hard the participants felt they were working at the time of giving the rating; and having the scale accessible (mounted between the handle bars within finger reach) at all times during testing.

Participants were introduced to wearing the wireless chest strap heart rate radio transmitter belt and practised fitting the mouthpiece and nose clip for the expired air analyses. They practised reading the RPE scale during low intensity cycle ergometry (keeping the pedal speed between 50 and 80 rpm through verbal cues if necessary) while wearing the heart rate monitor, mouthpiece, and nose clip. The pilot study determined that the correct pedal speed range (50–80 rpm) could be easily maintained, through verbal cues from the testing staff, without the use of a metronome. Once all participants had completed this practice session they were then asked to give their final informed consent.

Day 2: graded exercise test

On the second day, after a five minute low intensity warm up, all participants performed a graded maximal exercise test on the cycle ergometer using standard procedures^2,3 to determine maximal oxygen uptake (Vo₂max) and maximal heart rate (HRmax). Participants kept within the recommended pedal speed range of 50–80 rpm.

Days 2–5: production trials

After a period of at least four hours after the maximal test or on day 3, participants performed their first trial. A trial consisted of three exercise bouts at each of the three preselected RPEs (9, 11, and 13) performed in random order. Each bout consisted of three minutes of low intensity cycling, and then the work rate was adjusted, on command by the participant, to bring the intensity up to the appropriately produced RPE. Expired air and heart rate were measured continuously and recorded when the appropriate RPE and the work rate were unchanged for a period of four minutes, thus establishing steady state measures. Each exercise bout was followed by ten minutes of rest. As with the practice session and the maximal test, participants were thus notified verbally if they went outside of the pedal speed range of 50–80 rpm. The above production trial procedures were repeated twice more on separate days, between days 3 and 5, at the same time of day.

ANALYSIS OF DATA

The participants' ability to distinctly produce different exercise intensities for a given RPE was assessed using analysis of variance. A two factor repeated measures analysis of variance (RPE × trial) was used to test for differences between each of the three RPE levels and between each of the three trials for both %Vo₂max and %HRmax. α was set at p = 0.05. In cases in which analysis of variance showed a significant difference, a post hoc paired t test, with Bonferoni correction to reduce the possibility of a type I error (α reduced to p = 0.016), was performed to determine the location of pairwise differences.

In accordance with recent recommendations,^19,21 the participants' ability to reproduce the same exercise intensity (intertrial reliability) for a given RPE was assessed by the combined use of an intraclass correlation coefficient (ICC; model 2,1)³¹ and the bias±95% limits of agreement (95%LoA).²⁰ The ICC and 95%LoA analysis assessed intertrial agreement for %Vo₂max and %HRmax at each of the three different RPE levels for the following pairwise comparisons: trials 1 and 3 (T1–T3), trials 1 and 2 (T1–T2), and trials 2 and 3 (T2–T3). Statistical significance of the ICC was determined using the 95% confidence interval (95%CI). All analyses were performed on SPSS for Windows 8.0.

Results

The participants reported no difficulty in understanding or using the braille RPE scale. The group's HRmax and Vo₂max (mean (SD)) were 184 (5.5) beats/min and 2.2 (0.5) litres/min respectively.

VALIDITY

Table 1 summarises group values of %HRmax and %Vo₂max for the three trials at each of the three RPE levels (9, 11, 13). Analysis of variance showed a significant difference in both %HRmax (F = 38.2, p<0.0005) and %Vo₂max (F = 66.6, p<0.0005) between the three RPE levels. There was no significant interaction between trials and RPE levels for either %HRmax (F = 3.1, p = 0.10) or %Vo₂max (F = 0.58, p = 0.68). Post hoc t tests showed that all pairwise comparisons of the three different RPE levels were significantly different (p<0.016) with respect to both %HRmax and %Vo₂max.

RELIABILITY

Analysis of variance disclosed no significant differences across the three trials for either %HRmax (F = 0.56, p = 0.48) or %Vo₂max (F = 0.33, p = 0.72) at each of the three RPE levels (table 1). The variability within the 95% LoA for both %HRmax and %Vo₂max between trials (T1–T3, T1–T2, and T2–T3) decreased with successive trials for all three RPE levels. Tables 2 and 3 summarise the 95% LoA, and fig 2 provides a graphical example of these data. For %HRmax, the ICC increased with successive trials. Statistical significance, as identified by the 95%CI excluding zero (tables 2 and 3), was attained for all three RPE levels between T2 and T3. Similar results of T2–T3 for %Vo₂max were true for RPEs 9 and 11 but not for RPE 13, where the ICC (0.52) was not significant (95%CI −0.08 to 0.85).

For T2–T3, there was a positive relation between RPE level and the amount of variability in %Vo₂max (table 3; ICC and 95% LoA).

Discussion

The registered blind participants in this study were able to successfully use a braille RPE scale while performing cycle ergometry. They were able to use RPE to differentiate between intensity levels, and improved their ability to repeat a given intensity at the same RPE with each successive trial. Of course, finger reading of the braille scale was facilitated by the stationary position of the upper body during the cycle ergometry. It could be recommended that blind participants learn to use and memorise the scale from its braille format during cycle ergometry and then apply the concept during the use of other ergometers. Abadie¹⁰ found that, when sighted participants who were familiarised with RPE were asked to produce an RPE when the scale was not in view, exertion was underestimated. That study, however, used a treadmill, and it has been reported that using RPE during cycle ergometry provides better reproducibility than treadmill exercise.¹⁵

DIFFERENTIATING RPE LEVELS IN RELATION TO %VO₂MAX

Over the three trials, the RPE levels of 9, 11, and 13 equated to mean values of 47%, 53%, and 63% of Vo₂max respectively (table 1). These values fell within similar previously reported ranges for cycle ergometry.^14,25 The RPE range 12–16 is recommended for the development of both health based and rehabilitative cardiorespiratory fitness.^2,4 In keeping with these recommendations, at RPE 13, all our participants in all trials achieved the required exercise intensity range (50–80% Vo₂max) for developing cardiorespiratory fitness. The %Vo₂max values (table 1) were, however, quite varied among the individual participants. At RPE 9, 11, and 13, they were 35–62%, 40–65%, and 52–78% Vo₂max respectively. Dunbar et al³² have expressed concern about such between subject variability in the RPE-%Vo₂max relation, especially with respect to exercise prescriptions for older less well trained people. An important reason for between subject variability at a given RPE is endurance fitness (training status).^33,34 RPE during cycle ergometry and treadmill exercise were reported as being more strongly related to the lactate or ventilatory threshold than to %Vo₂max. The more highly trained subjects exercised at a higher %Vo₂max for a given RPE than their less trained counterparts. During exercise to music or circuit based exercise, training status appears to be less of a mediator in the RPE-%Vo₂max relation.³⁵ In general, however, it would seem sensible that exercise prescriptions using RPE should account for a subject's training status.

INTERTRIAL RELIABILITY

Our results confirm previous observations^25,36 that reliability of using RPE improves with more than two trials. The Bland and Altman²⁰ plot in fig 2 illustrates how heart rate response becomes less variable with each successive trial. Most of the RPE production mode multiple trial studies have used a motorised treadmill.^{22–24,26,27} Our study adds to the number of studies^15,16,25,36 that have used the cycle ergometer to evaluate variability and reliability of reproducing a given exercise intensity with RPE. In using heart rate alone to judge the reliability of RPE to reproduce a given exercise intensity, the ICC and 95%LoA results (tables 2 and 3 and fig 2) showed that, after two trials, RPE provided a high level of reliability. With the same analysis, but using Vo₂ as the criterion, the reliability argument is somewhat weakened at higher intensities (RPE 13; >55%Vo₂max). Our results therefore highlighted two questions: (a) how well can heart rate on an interday basis be used as a reliable marker of exercise intensity and (b) should heart rate therefore be used as a means of evaluating the reliability of RPE? Interestingly, Dishman⁵ concluded that, within the range 50–70%Vo₂max, the reproduction errors in Vo₂ were no greater when using a target RPE than when using a target heart rate.

Similar to the results of Lamb et al,¹⁹ our application of the 95%LoA analysis (tables 2 and 3, fig 2) showed that between a first and second trial, there was lack of good agreement for many of the individual participants' scores. For example, for %Vo₂max between T1 and T2, which is a typical test-retest scenario, the 95%LoA ranges for RPE 9, 11, and 13 were ±15.8%, ±20%, and ±15.7% respectively. Unlike Lamb et al,¹⁹ we performed a third trial analysis (T2–T3), in which agreement further improved at RPE 9 and 11: the 95%LoA ranges decreased to ±10.6% and ±13.2% respectively. These were reductions in variability by a factor of 1.5. Unfortunately, at the higher intensity of RPE 13 (>50%Vo₂max), more trials are required to attain such an improvement in intertrial agreement/reliability. In line with the recent available recommendations¹⁹ for sighted people, blind participants using RPE in braille also require at least two repeated exposures (habituation) to achieve acceptable reliability. It must be acknowledged, however, that Lamb et al¹⁹ evaluated RPE in estimation mode using progressive treadmill exercise, whereas our study used two distinctly different variables: steady state RPE in production mode and the use of a cycle ergometer. It is therefore yet to be clearly established whether or not between trials variability and thus reliability are also functions of RPE mode (estimation, production, preferred).

CONCLUSION

These findings show that, when a group of healthy registered blind participants employed a braille RPE scale in production mode to control cycle ergometer intensity, they produced similar cardiorespiratory responses to those outlined in recommended guidelines for healthy sighted people. Furthermore, factors affecting multiple trial reliability are comparable with those in similar studies with sighted subjects. The results highlight that between trials reliability of RPE is a function of the number of trials performed. When RPE reliability is judged by %Vo₂max and evaluated using a combined analysis of an ICC and limits of agreement, our results show that at least two separate exposures are required in the RPE range 9–12. Attaining exercise intensity reliability for RPE >13 using the braille scale in this group of participants requires more than three trials. RPE in braille during cycle ergometery can be used by healthy blind people, with similar effect to the existing exercise testing/prescription guidelines for healthy sighted people. Future studies should include: a between trials reliability comparison of RPE for sighted versus blind; exploration of the number trials required, as judged by %Vo₂max, for RPE to become reliable at higher intensities; determination of the means by which RPE is mediated by the mode (production, estimation, preferred) in which it is used.