The subjects participating in this study self-reported an average of more than 10 years of RT experience. Men were stronger than women in absolute strength (p < 0.001) and had greater height and weight (p < 0.005, Tables 1 and 3), but there were no sex differences in the relative 1RM (as %BW).
Subjects responded to the question: “Did you feel like the foot plate would fly off of your feet if you pushed as fast as possible?” affirmatively when experiencing loads on this cable pulley leg press machine that were less than or equal to approximately 50% 1RM, which corresponded with an RPE of less than or equal to approximately 11.
Borg RPE ratings were found to significantly predict loads relative to the 1RM for older adults with RT experience, resulting in the acceptance of the experimental hypothesis. The load-RPE relationship presented in this study may be useful when training older adults using ERT on the leg press. For example, commonly selected RT loads that elicit strength and power gains (≥70% 1RM, as suggested intensity for RT by Pollock et al. (37)) were identified with an RPE of ≥14 in this study using the leg press. It is important to note that the subjects' ratings were obtained before their 1RM test, so their ratings were solely based on their reflection of the perception of the load with the numbers and qualitative phrases on the Borg RPE scale and not based on a recent experience with the sensation of the loads used during a 1RM test. This makes this approach feasible for regulating ERT loads in the absence of a 1RM test in a fitness center.
The resulting load-RPE relationship seems to be reasonable for use in an RT setting; a load that would be considered high intensity (e.g., 80% 1RM) corresponds to an RPE of 15–16, corresponding to a qualitative description of “hard” on the scale. Very high–intensity loads (e.g., 90% 1RM) relate to the range of 17–18 on the RPE scale, corresponding to a qualitative description of “very hard.” Loads less than 60% 1RM, and therefore less useful for improving muscle strength, align with an RPE of 11 and lower on the RPE scale, corresponding to a qualitative description of “fairly light” at the highest intensity within that range. This load-RPE relationship may represent a useful depiction of the desired perceptions for older adults during ERT of various loads, opening the door to the elimination of maximal strength testing as a means of regulating intensity during ERT. The load-RPE relationship appears to be less useful in the highest range of the scale, where a “maximal” exertion of 18–20 corresponded with a range of 99–112% 1RM, whereas the intention of the score of 20 is that it would represent 100% 1RM.
The results of the present study do not conform with results obtained by Lagally et al. (27) for the lower loads, as they found a 30% 1RM load to correspond to a rating of 13.0 (somewhat hard) on the Borg RPE scale, whereas in the present study, an RPE of 13 corresponded with 67% 1RM. This difference is likely because of the previous study's methods of anchoring the low and high ends of the RPE scale to unweighted and 1RM leg press loads, respectively, as did Gearhart et al. (13), who also used the 15-point RPE scale (ranging in rating from 6 to 20) during RT with young adults on several different upper and lower extremity exercises, identifying 90% 1RM and 30% 1RM as approximately 14–15 and approximately 8–10 on the RPE scale, respectively. This process involved a detailed method of “anchoring” the low and high end of the RPE scale to the sensation of performing the lift with no load and at 1RM. The present study aimed to provide a simple and straightforward method for identifying ERT loads in a fitness center, and so a set of instructions identifying a baseline rating of 6 for the leg press with no load and a maximal rating of 20 for the 1RM, as in Gearhart et al. (13), was not used. In the present study, RPE successfully and strongly linearly predicted the %1RM for loads between 30 and 100%1RM. The more time-consuming anchoring procedures used in previous studies (13,27) appear to be unnecessary for characterizing useful ERT loads using the standard RPE scale with only a simple explanation to the people who exercise.
Several limitations can be identified that affect the applicability of these results to all older subjects. The study procedures took place in the summer season, and it is possible that increased summer physical activity rates may influence the results of this analysis (6). However, the leg press 1RM values for the subjects in the present study (Table 4) compare well with the average baseline leg press results for older adults in previous RT studies, which have ranged from 64 to 123 kg for older women (1,10,23) and 113 to 175 kg for older men (5,7,18,20,21,23). Furthermore, the present study included older adults who are accustomed to RT but who had no experience with ERT. It remains to be seen whether a similar load-RPE relationship would also exist between ERT loads and RPE for older adults with no experience in RT, but previous research revealed no difference in RPE and muscle activity between experienced and novice lifters for young adults performing bench press (26), and the authors of that study noted this finding as a support for the use of RPE to regulate exercise intensity for both experienced and inexperienced weightlifters.
It is unknown whether this study's results would also be found using different exercise machines other than the leg press. Furthermore, it is unknown whether the use of RPE to determine loads for ERT will be effective in long-term programs with older adults, although there is some evidence that RPE increases over the course of a training program along with increases in the absolute training load (43). Additionally, the regulation of RT load using constant-RPE tracking (where the RPE is used to identify a constant relative load) appears to have both promise and limitations for RT in older adults, given that RPE predicted the same %1RM after exercise for some exercises and loads, although not all (14). The usefulness of RPE through a training program, as a method of regulating the load used during ERT, is yet to be established.
Six subjects did not reach a true 1RM because they stopped the test because of their concerns regarding the potential for injury at such high loads; thus, it is unclear how far from their true 1RM these subjects were, and because the loads were represented as a percentage of the 1RM, it is uncertain how much this would have affected the RPE at each load for these subjects. These subjects' 1RM was designated as the last load they completed during the 1RM test. If this 1RM approximation was much less than the true 1RM, then each relative load would be overestimated compared with if a true (higher) 1RM had been measured (e.g., 80 kg is 67% of a 1RM of 120 kg, but if the true 1RM was 130 kg, then 80 kg would actually be 61.5% 1RM). This inflation of the relative loads for these subjects likely contributed to the overestimate of 112% 1RM at RPE = 20 in the present study. However, each of these subjects rated the last load they lifted as RPE 19 or 20, indicating that they were likely near their personal 1RM. When excluding these subjects from the analysis, an RPE of 20 estimated 104–108% 1RM for the linear and polynomial models and 111% for the power model, which is still an overestimate of the %1RM that an RPE of 20 should represent.
Although not measured, the nutritional and hydration status of the subjects were presumed to have remained unchanged, as subjects were tested within 1 week apart at about the same time of day for both session 1 and session 2, and this time typically corresponded to the subjects' preferred training time (the subjects were tested during the time they usually arrived for RT).
Explosive resistance training at both high-intensity and low intensity loads is desirable because the range of intensities improves muscle strength, power, balance, and functional capacity in different and important ways in older adults. There is a need for simplified methods for regulating ERT intensity with older adults, to make ERT more accessible for personal trainers and their older adult clients (i.e., not requiring a maximal strength test). The load-RPE relationship resulting from the present study reveals that the numbers and qualitative ratings on the standard Borg RPE scale predict relative seated leg press loads on a cable pulley RT machine. Therefore, the numbers on the scale can be used as a guide to select the intended load for ERT. For example, an RPE between 14 and 16 corresponds to loads in the range of approximately 70–90% 1RM for ERT, a stimulus that is known to significantly improve leg press strength and power simultaneously in older adults (7). Additionally, an RPE lower than 12 corresponds to loads less than approximately 60%, which is the range of ERT intensity that is related to balance function (32).
This study also revealed that loads less than or equal to approximately 50% 1RM (corresponding to less than or equal to approximately 11 on the RPE scale) are potentially problematic on a leg press cable pulley RT machine because subjects reported, during these light loads, that the leg press foot plate would have projected off of their feet had they pushed as fast as they could. The hazard of this occurring is that the foot plate would then rapidly return to the starting position, potentially injuring the client. Such light loads, therefore, should be avoided when conducting ERT on a cable pulley leg press machine. On the other hand, moderate to high loads were safely conducted using ERT methods with this population on a cable pulley leg press machine.
It is yet unknown whether the load-RPE relationship would be effective for regulating training intensity throughout the course of an ERT intervention (e.g., it remains unknown whether an RPE of 14–16 would consistently relate with a relative load of approximately 70–90% 1RM throughout an ERT program). It is also unknown whether the load-RPE relationship identified here would apply similarly to other exercises beyond the leg press.
Even before the full impact of the load-RPE relationship is understood for ERT, the present study's results can be implemented by personal trainers who aim to improve strength and power simultaneously in their older adult clients, without requiring maximal strength testing, by the following: (a) directing older clients' attention to the Borg RPE scale; (b) providing a description of the meaning of the 6- to 20-point ratings using the original accompanying qualitative descriptor words; (c) selecting a load that the client rates within the range of an RPE of 14–16, corresponding to an intensity of approximately 70–90% 1RM; and (d) training the client to increase the velocity with each repetition until it is as fast as safely possible during the concentric phase while avoiding locking the knee before the eccentric phase and conducting the eccentric phase in a slow and controlled manner.
The authors would like to acknowledge the contributions of C. Scott Hollander and Angela Roake for their work on the data collection aspect of this project and other administrative tasks, and Gordon Chalmers for his helpful reviews of the article. The authors further acknowledge Western Washington University for providing the summer research grant that made this work possible.
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