Ratings of perceived exertion (RPE) have been assessed for the overall body and the active muscles during resistance exercise (3,5-8,12-14,17-19). Consistent results indicate that RPE increases during an exercise bout whenever resistance is added (3,4,6,7,10,15-18), regardless of the physical work (i.e., repetitions and resistance) performed (7,15) and that increases in RPE are linked to increases in select physiological variables, such as lactic acid concentration and muscle activity (6,7,16). Based on these results, it has been suggested that RPE can be used during resistance exercise to (a) prescribe training intensities, (b) guide daily training dosages, and (c) track training progress (14).
The findings that perceived exertion and physiological variables are linked during resistance exercise are in line with Borg's model of the Effort Continua (1). The model indicates that all individuals will demonstrate a similar correspondent perceptual-physiological link. This means that RPE will be similar among all individuals when the intensity or workload is similar (i.e., relative to individual maximal levels). According to this model, subjective responses to exercise rely on 3 effort continua: (a) physiological, (b) perceptual, and (c) performance. A functional link among these 3 effort continua suggests that both perceptual and physiological variables can provide similar information about performance. As such, during resistance exercise, the perceived exertion reported during a lift would provide similar information about the intensity of the lift as the level of muscle activity involved, or other physiological markers of exercise intensity. Another application of Borg's model is that RPE can be used as a method of tracking training progress or strength tracking. In terms of resistance exercise, strength tracking can occur by using RPE as a reference value to monitor changes in muscle strength as a function of a resistance training program. In this case, as physiological variables, such as [HLa] and muscle activity, change at a given workload with changes in muscle strength, RPE should also change. A study by Pierce et al. (13) found a reduction in blood lactate and heart rate and a corresponding reduction in Borg scale RPE after 12 weeks of high-volume resistance training when comparisons were made using an absolute load. Maximal strength increased after training, so the weights lifted at the post-training time point represented a lower percentage of maximal. These results suggest that RPE may reflect changes in physiological variables associated with an increase in strength, and thus, in agreement with Borg's model of the Effort Continua, provides information about performance (i.e., a change in muscle strength).
Strength tracking using RPE may be particularly beneficial for older adults because it may reduce or eliminate repeated 1 repetition maximum (RM) testing used to assess changes in strength. In a study of 70- to 79-year-old subjects, nearly 20 % of all injuries in a walk/jog and variable resistance training investigation occurred during 1RM strength testing (2,15). Also, according to the Pierce et al. study (13), when strength increases, RPE decreases for a given load. Thus, as training continues, the resistance required to achieve the target RPE would increase (16). When used in this manner, RPE would eliminate the need for older adults to participate in the heavy lifting associated with 1RM tests because resistance would be automatically adjusted without reassessing strength. Using RPE during resistance exercise may also be useful because older adults may already modify their resistance for a variety of exercises based on subjective feelings caused by existing conditions, such as arthritis or other general aches and pains that are more common in the older population. However, to our knowledge, no information is available using RPE during resistance exercise in the older adult population, so it is unknown whether or not RPE can be used in this way for strength tracking in this group.
Because older adults are more likely than younger adults to have a limited training background with resistance exercise, the OMNI-resistance exercise scale (OMNI-RES) may be the appropriate RPE scale to use with this population. OMNI scales include mode specific pictorials, numerical ratings, and corresponding verbal descriptions that are distributed along an increasing intensity gradient. Earlier scales contain only numerical and verbal descriptions of perceived exertion. It is proposed that the inclusion of visual, numerical, and verbal perceptual descriptors aid individuals who rely on visual, hierarchical, verbal, or some combination of the 3 types of cues to rate their perceived intensity of exertion. Both concurrent and construct validity have been established for the OMNI-RES using the Borg 15-category scale as the criterion metric during an acute bout of resistance exercise (7, 18). Furthermore, it has been suggested that the OMNI-RES is an effective tool to use with beginning exercisers as it provides a simple, subjective guide to aid in determining safe and appropriate resistance training intensities (16). Therefore, the purpose of the present study is to determine if the OMNI-RES could be used to track training-induced strength changes in older adults (Figure 1).
Experimental Approach to the Problem
Height, weight, and percent body fat (Dual X-ray Absorptiometry) were measured upon arrival to the laboratory. At the orientation session, memory anchoring instructions, as described by Robertson et al. (18), were provided for the high and low anchor on the OMNI-RES. The subjects underwent 2 weeks of resistance exercise training (RET) orientation (3 days a week). The same workout that was performed during the training (see training section) was performed during the orientation sessions. However, the intensity was maintained at a low level by having subjects adjust the resistance to correspond to an RPE of 4. An RPE of 4 (i.e., somewhat easy) on the OMNI-RES corresponds to 11 (i.e., light) on the Borg 15-category scale (7). Each day and for each set, the resistance was modified to maintain an RPE of 4 (OMNI-RES). The orientation was performed to induce the neurological component of strength to get true strength measures and to reduce the rate of injury associated with initiation of intense resistance exercise programs.
One Repetition Maximum Testing and Ratings of Perceived Exertion Data Collection
After the orientation sessions, testing was performed to assess the 1RM for each of 7 exercises, including the leg press, latissimus dorsi (lat) pull-down (Cybex, Cybex International, Inc., Medway, MA), chest press, leg extension, leg curl, arm extension, and arm curl (Cybex, Cybex International, Inc., Medway, Mass.)performed in this sequence. The 1RM tests were performed in this order, and the order was the same for all subjects both before and after training. Using the subjects' experience with an OMNI-RES RPE of 4 and the investigators' judgment, the initial weight was chosen for the 1RM test protocols. Subjects progressively lifted increasing amounts of weight until only 1 repetition could be completed. A 1-minute rest period was provided between each lift. The time required to choose the resistance for the subsequent lift was minimal because it was completed before the 1-minute rest period between lifts had expired. At the end, when 1RM was attempted, and effort was made to minimize the number of attempts required to achieve max. Subjects were encouraged to lift additional resistance to be sure that maximal muscle force was achieved. Most 1RM trials resulted in concentric muscle failure. Only when it was clear from their effort that no further resistance could be added was a nonfailure trial accepted. The 1RM was determined to be the most resistance the subject could concentrically lift at once. After each lift throughout the 1RM test for each exercise, subjects reported their overall RPE from the OMNI-RES. This provided a series of estimated perceived exertion responses across a range of resistances from light to heavy both pre- and post-training, similar to how estimation of RPE occurs during a graded exercise test.
Three days a week for 12 weeks, subjects participated in a supervised RET program that included 10 minutes of cycle ergometry warm-up, 5 minutes of dynamic stretching, and 3 sets of 8-12 repetitions for the 7 resistance exercises, performed in a counterbalanced order, with resistance set at 75 % of the exercise specific 1RM. Exercises included the leg press, lat pull-down (Cybex, Cybex International, Inc., Medway, MA), chest press, leg extension, leg curl, arm extension, and arm curl (Cybex, Cybex International, Inc.). Subjects were instructed to perform as many repetitions as possible unless they achieved 12 repetitions. When a subject achieved 3 sets of 12 repetitions on an exercise, the resistance was increased to a level where only 8 repetitions were possible. Subjects rested for 60 seconds between sets and for 2 minutes between exercises. After the 12-week intervention, the 1RM protocol, as described above, was performed for each exercise.
Subjects were recruited by broad advertisements and included men and women age 60-69 years old who were generally healthy, nonsmokers, and able to perform RET and training. The subjects ranged from sedentary to recreationally active. All testing was approved by the Institutional Review Board at Kent State University, Kent, Ohio. Twenty-two men (64.3 + 3.2 years) and 27 women (63.8 + 2.8 years) volunteered to participate. Signed, written informed consent was obtained from each subject before participation. Subjects were excluded if a medical history or physical exam by a nurse practitioner revealed blood pressure >160/100 mm Hg, cardiac arrhythmias, cancer, hernia, aortic aneurysm, kidney disease, or lung disease. Pretraining descriptive data for subjects are found in Table 1.
Alpha was set at 0.05. Differences in pre- and post-training 1RM values were determined using paired samples t-tests. Linear regression using RPE as the independent variable, and resistance lifted (kilogram) as the dependent variable was determined for pre- and post-RET for each subject. This was performed to predict pre- and post-training resistance lifted at the criterion RPE of 4, 6, and 8. Differences in these predicted values were examined using paired samples t-tests. Analyses were performed using SPSS software version 14.0 (SPSS Inc., Chicago, Ill.).
The results of the paired samples t-tests examining differences in 1RM indicated that the 1RM increased from pretraining to post-training (p < 0.05) for all exercises (Table 2). The t-tests examining the pre- and post-training resistance lifted at given RPE values indicated that the absolute load lifted (kilogram), as predicted from the individual regression analyses, increased at each criterion RPE (i.e., 4, 6, and 8) (p < .05) after the 12-week training session (Table 3) for every exercise.
The purpose of this study was to evaluate the use of OMNI-RES RPE as a method of tracking strength changes in an older adult population. Borg's model of the Effort Continua (1) suggests that subjective responses to exercise rely on the 3 effort continua of (a) physiological, (b) perceptual, and (c) performance and that a functional link exists among these three continua. Thus, perceptual responses to exercise should provide similar information as physiological responses about exercise performance. With resistance exercise, the effort continua model would suggest that as strength changes because of RET, perceptual responses should reflect those changes. The results of the present investigation agree with the effort continua model in that a 12-week RET program resulted in an increased muscular strength and an increase in the absolute load lifted at 3 criterion OMNI-RES RPE (i.e., 4, 6, and 8) in older men and women.
These results are similar to the results found for younger subjects by Pierce et al. (13). In that study, after high-volume strength training, subjects reported a reduced RPE at each absolute load, indicating that as training induced changes in muscular strength, RPE from the Borg 15-category scale was able to track these changes. This is the reciprocal of the present findings where RPE was kept constant and load was allowed to vary. During the 12-week resistance exercise program, the 1RM increased as expected. The resistance required to produce each criterion RPE also increased. As such, a heavier absolute load was required to produce the criterion RPE at the post-training time point as compared with the pretraining time point. It is believed that this is the first investigation to use RPE to track training-induced strength changes in a male and female hexagenarian population. The present results indicate that for a given RPE, older adults lift more weight as muscular strength increases. The results were consistent across upper- and lower-body exercises, as well as between large- and small-muscle groups. This provides an RPE-based procedure to track strength training changes during a variety of resistance exercises using the OMNI-RES. For example, a target RPE could be prescribed throughout the length of a given strength training program, and the resistance could be manipulated based on the subjective feelings of exertion. Tracking strength in this manner may be of particular importance with an older cohort because the incidence of injury has been shown to be high with 1RM testing in this group (2,15). Additionally, there is some evidence that using RPE to regulate intensity may increase compliance (2,4,15) to an exercise program.
Pierce et al. (13) have indicated that after high-intensity resistance training, subjects indicated a reduced RPE at the same absolute load using the Borg 15-category scale. The present investigation produced similar results using the OMNI-RES. A possible advantage of OMNI-RES over the Borg RPE scale is that the inclusion of pictorial, numerical, and verbal perceptual descriptors aid individuals who may rely on different types of cues (i.e., visual, hierarchical, or verbal) to rate their perceived intensity of exertion. This makes the OMNI-RES applicable to a wider range of individuals than scales that contain fewer types of descriptors. The results of the present study indicate the OMNI-RES is an appropriate metric to track strength changes in older adult men and women.
Previous research using the OMNI-RES was performed on young, recreationally trained subjects. This presents a possible limitation to the present investigation. While the OMNI-RES has not been validated with an older population, the results of the present study suggest that there is a link between RPE and resistance exercise intensity in seven different exercises. Furthermore, there is no reason to believe that older individuals would not exhibit the same links between RPE and physiological variables as younger people. However, it would be worthwhile to examine the possible mediators of RPE in an older population in the future. Future research of interest could also examine the given RPE required to induce changes in not only muscular strength, but also endurance and hypertrophy, to provide information on the target RPE values that might be used in resistance exercise prescription to achieve each muscular fitness goal.
In summary, the results of the present study indicate that as muscular strength improves, older adults may track the strength changes from a resistance exercise program using RPE from the OMNI-RES. When exercise is prescribed at a given RPE, it seems that the prescribed RPE continues to be useful, even as strength increases, because the resistance required to achieve the target RPE also increases. This result is consistent with Borg's model of the effort continua. One benefit of regulating resistance training intensity using RPE is that the training load could be manipulated as strength increases without the need for 1RM testing, which may reduce the risk of injury during strength training programs.
The present results may have implications for the clinician or personal trainer working with older adults. As older adults train, strength gains become apparent, and training adjustments must be made for continued progress. It seems that RPE from the OMNI-RES can be used to track strength changes over time in older adults. Given the present results, which demonstrate that the resistance lifted at a given RPE will increase after training, the use of a target OMNI-RES RPE will automatically provide an upward adjustment of training load as adaptations occur. This RPE-based adjustment of resistance could possibly increase exercise adherence as well as eliminate the need for repeated 1RM testing and thus reduce injury from maximal testing in this population.
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