Impact of Testing Strategy on Expression of Upper-Body Work Capacity and One-Repetition Maximum Prediction after Resistance Training in College-Aged Men and Women

Abstract

Mayhew, JL, Brechue, WF, Smith, AE, Kemmler, W, Lauber, D, and Koch, AJ. Impact of testing strategy on expression of upper-body work capacity and one repetition maximum prediction after resistance training in college-aged men and women. J Strength Cond Res 25(10): 2796–2807, 2011—The purpose of this study was to assess the effect of resistance training on upper-body muscular strength and the expression of work capacity and muscular endurance. In addition, a training-induced change in the relationship between muscular strength and endurance was assessed by testing changes in the accuracy of using endurance repetitions to predict 1 repetition maximum (1RM) bench press before and after training. College-aged men (n = 85) and women (n = 62) completed a 12-week linear periodization resistance training program. Before and after training, the subjects were assessed for 1RM and repetitions to fatigue (RTFs) with a submaximal load. After pretraining 1RM determination, the subjects were randomly assigned to perform RTFs at 65% 1RM (n = 74) or 90% 1RM (n = 73). Pretraining and posttraining RTFs were conducted at the same respective %1RM. Work capacity was determined from repetition weight × RTF. After training, there was a significant increase in 1RM in both men (∼14%) and women (∼23%). Posttraining RTF was not different from pretraining RTF at 65 %1RM (18.2 ± 5.1 and 19.0 ± 6.0, respectively) but was significantly reduced in the 90% 1RM group (6.1 ± 3.6 vs. 4.5 ± 2.7, respectively). Likewise, there was a differential effect of training on the expression of work capacity, which increased in the 65 %1RM group (123 ± 155 kg-reps) but decreased in the 90% 1RM group (−62 ± 208 kg-reps); the effect was independent of gender within each testing group. In conclusion, the changes in muscular strength associated with resistance training produced an increase in work capacity when tested with a 65 %1RM load without a change in endurance. In contrast, both work capacity and endurance decreased when tested with 90% 1RM. Thus, the impact of strength training on work capacity and muscle endurance is specific to the load at which endurance testing is performed.

Introduction

Resistance training often has 2 major objectives: to increase muscular strength and improve muscle endurance and work capacity (^4,22,41). Each objective may be important to differing degrees at varying times during the training cycle for athletes, occupational specialists, fitness participants, and rehabilitation patients. The degree of emphasis placed on each objective depends on the major requirement of the individual undergoing the training. Although the primary objective of most resistance training programs is typically focused on an increase in muscular strength, the ability to enhance muscular work capacity may also be important. One approach to determining work capacity may be the product of maximum repetitions with a given load. Thus, an improvement in work capacity might indicate an increased ability to perform repetitive daily work tasks, enhance recreational sports capabilities, or hasten the rehabilitation process. Although muscular strength and work capacity are generally assumed to be related, the association remains questionable and is most probably defined by training state and set and repetition patterns used in a training program (^1,6,7).

Most training programs are designed based on various combinations of sets and repetitions, regardless of the training level of the individual. If we accept the validity of the training specificity principle, there should be a direct relationship between the training stimulus and the response, that is, individuals should make the greatest gains when the exercise overloads a specific area of the energy continuum (^22,23). In resistance training, the use of heavy loads and few repetitions should produce maximum gains in strength, whereas light loads and many repetitions should produce the greatest improvements in muscle endurance. Anderson and Kearney (¹) had earlier noted that when training, intensity groups were based on repetition “windows” (low = 6–8 reps; medium = 30–40 reps; high = 100–150 reps), the high-load, low-repetition group did not improve significantly in work capacity after training, whereas the other groups did. Campos et al. (⁹) produced similar findings using low-rep (3–5 repetition maximum [RM]), intermediate-rep (9–11RM), and high-rep groups (20–28RM), with the former making the greatest gains in strength (1RM) and the latter making the greatest gains in local muscle endurance.

Despite the dictates of the specificity principle, most resistance training programs tend to focus on the production of maximal strength gain. In previous years, these programs used a traditional approach of multiple sets with fixed RM loads. In recent years, however, resistance programs have centered on various forms of the periodization technique (^4,22,41). Recent studies comparing linear and nonlinear periodization programs have noted no significant difference in the strength gains from these approaches (^2,3,30-32). The work of Rhea et al. (³³) is one of the only studies directed at the effect of periodization on muscle endurance. They found that a reverse linear periodization model, in which the intensity was reduced and the volume increased over 15 weeks of training, augmented muscle endurance more than a progressive increase in intensity with a reduction in volume. Given that few studies have observed changes in muscle strength, muscle endurance and muscle work capacity during resistance training, it seems advisable to evaluate these parameters that result from a program specifically designed to increase strength. Therefore, the purpose of this study was to assess the effect of resistance training on upper-body muscular strength and the expression of work capacity and muscular endurance in young men and women. In addition, a training-induced change in the relationship between muscular strength and endurance was assessed by testing changes in the accuracy of using endurance repetitions to predict 1RM bench press before and after training.

Methods

Experimental Approach to the Problem

Previous sources have suggested that resistance training using heavy loads (>85% RM) to perform low repetitions (<5 repetitions) emphasize muscular strength development (^22,23,41). When higher numbers of repetitions are performed, the emphasis of the resistance program may shift to the development of muscle work capacity (¹). A popular and productive training method applies the linear periodization principle, where repetitions are progressively reduced and loads increased over various training cycles (⁴). Although this approach appears to maximize strength development, limited information exists concerning its effect on muscle work capacity. Furthermore, almost no information is available concerning the effect of periodized resistance programs on the development of both strength and work capacity in untrained women.

Given the importance of both muscular strength and work capacity in various settings, this study sought to evaluate the effect of a short-term, periodized resistance program on the development of muscular strength and the enhancement of muscular work capacity in previously untrained men and women. Work capacity, calculated from the product of load (RepWt) and repetitions to fatigue (RTFs), was evaluated by dividing the subjects into 2 testing groups to test RTFs at either 65% 1RM or 90% 1RM, thus encompassing a wide range of the load-repetition continuum. Furthermore, we evaluated the relationship between maximal strength and muscular endurance across this wide range of repetitions through regression and equations predicting 1RM.

Subjects

College-aged men (n = 85) and women (n = 61) volunteered to undergo a linear periodization resistance training program as part of a required fitness program. The subjects were untrained at the start of the study, having not participated in a regular training program within the previous 6 months.

During the course of the study, no attempt was made to control the diet or hydration level of the subjects, although classroom discussions provided proper nutritional information for improving general wellness. Weight training instructors emphasized the need for adequate hydration and encouraged the participants to bring water bottles during training. The study was fully explained to the subjects, and written consent was obtained before the study. The protocol was approved by the Institutional Review Board of the university. Physical characteristics of the subjects by group are shown in Table 1.

Table 1: Physical characteristics and pretraining and posttraining performance characteristics of the 65% 1RM and 90% 1RM testing groups.*†

Procedures

Before strength assessment, the subjects were measured for height, weight, and 3 skinfolds. Height was measured with a stadiometer, and weight was determined from a certified balance scale accurate to 0.1 kg (Homs, model 150KTM, Homs Corp., Buffalo Grove, IL, USA). Skinfolds were measured in triplicate by an experienced investigator at the triceps, suprailiac, and thigh sites for women and the chest, abdomen, and thigh sites for men using Harpenden calipers (John Bull Ltd., London, England). The reliability for skinfold measurement for this investigator had previously been determined to exceed 0.95. The sum of the average of the 3 measurements at each site was used to estimate body density using generalized prediction equations (^19,20). Fat mass (FM) was estimated as body mass (BM) × %fat/100. Fat-free mass (FFM) was determined as BM − FM.

During the first week of the study, the subjects were evaluated for 1RM free-weight bench press. Testing followed a standard “touch-and-go” protocol in which the bar was lowered slowly to touch the chest before being pressed immediately to full-arm extension (^22,41). During testing, each subject performed a warm-up according to personal preferences using light weights of approximately 50–70% of the estimated 1RM for several sets. When testing began, a weight was selected, and 1 repetition was performed. A minimum of 5 minutes rest was given before attempting subsequent repetitions. After a successful repetition, weights were added, ranging from 1.1 to 6.8 kg, according to the perception of effort of the previous repetition. This approach allowed most subjects to reach their 1RM within 3–5 attempts. A spotter assisted in the lift-off to place the bar above the chest in a straight-arm position before each 1RM attempt. Reliability for 1RM has previously been established on similar populations at 0.93–0.97 (^15,17,34).

After the initial 1RM test, members of each gender were randomly assigned to 1 of 2 intensity groups to test RTF: either 65% 1RM (n = 74) or 90% 1RM (n = 73). The subjects then completed the RTF test at their specific load (group assignment). At least 48 hours of recovery was allowed between the 1RM and RTF test.

To perform the RTF test, each subject completed a warm-up of 2–3 sets with light weights (30–40% of 1RM), then rested for 5 minutes before completing the RTF test. Although no cadence was used, the subjects were encouraged to maintain a steady rhythm and to raise and lower the bar through a full range of motion. Work capacity was calculated as repetitions (RTF) times the load (RepWt). Reliabilities between 0.87 and 0.95 have been noted for RTF in similar populations (^15,17,34).

Resistance Training Program

All the subjects then underwent the same 12-week linear periodization resistance training program 3 d·wk⁻¹. Core lifts of bench press and squat followed a program of 3 × 10–12RM during the first 5 weeks, 3 × 6–8RM during the next 4 weeks, and 3 × 3–5RM during the final 3 weeks. Auxiliary exercises included seated behind-the-neck press, arm curls, lat pull-downs, upright rows, and calf raises and were performed in 3 sets of 10RM throughout the study. Training weights were incremented for auxiliary exercises when the subject could perform >10 repetitions in each set.

Posttraining Testing

After the 12-week training program, the subjects again completed a 1RM test and an RTF test at the same relative load as in the pretest (according to group assignment). All posttesting was completed at the same time of the day, using the same testing procedures, equipment, and testing personnel as in the pretest. Figure 1 illustrates the study design.

Figure 1: Testing and training program during the 16-week study.

Statistical Analyses

A 2 × 2 (intensity × gender) mixed factorial analysis of variance (ANOVA) was used to identify significant differences in the dependent variables before and after training. When significance at p ≤ 0.05 was noted, a Bonferroni post hoc test was used to isolate the differences. Statistical power ranged from 0.58 to 0.90 for all analyses. Comparisons between predicted and actual 1RM bench press performances were made using a repeated measures ANOVA with Bonferroni post hoc comparisons and interclass correlation coefficients (ICCs). Multiple regression analysis was used to determine the relative contribution of selected variables in estimating a criterion variable.

Results

Pretraining Measurements

There were no significant differences in physical characteristics between the groups (Table 1). Independent of testing group, men were taller, heavier, had more FFM and less %fat than women did (Table 2). For submaximal RTF testing, the 90% 1RM group used significantly greater RepWt and RepWt/kg, which produced significantly fewer RTFs and lower work capacity than the 65% 1RM group (Table 1).

Table 2: Physical characteristics and pretraining and posttraining performance characteristics by gender, independent of testing group.*†

Bench press strength was positively related to BM, FFM, and work capacity and negatively related to FM and %fat in both intensity groups (Table 3). In the 65% 1RM group, RepWt had a higher correlation with work capacity at the pretraining (r = 0.86) and posttraining measurement (r = 0.80) than did RTF (r = 0.43 and 0.40, respectively). Analysis of the standardized regression coefficients from linear regression indicated that RepWt accounted for a larger portion of the known variance (pretraining = 78% and posttraining = 72%) than did RTF (22 and 28%, respectively). In the 90% 1RM group, RepWt had a lower correlation with work capacity at the pretraining (r = 0.49) and posttraining measurement (r = 0.46) than did RTF (r = 0.64 and 0.68, respectively). Analysis of the standardized regression coefficients from linear regression indicated that RTF accounted for a larger portion of the known variance (pretraining = 58% and posttraining = 62%) than did RepWt (42 and 38%, respectively).

Table 3: Relationship between muscular strength (1RM bench press) and selected variables in the 65% 1RM and 90% 1RM testing groups.*†

When divided by gender, men used a significantly greater RepWt and RepWt/kg, which produced a significantly greater work capacity at both testing intensities than women did (Table 4). Given the gender differences in 1RM and BM, it was interesting that work capacity was similar between men tested at 90% 1RM and women tested at 65% 1RM (Table 2). The relationship between muscular strength (1RM) and RTF was not significant within either intensity test group (Table 3) or within either gender (Table 5) and accounted for <4% of the shared variance between the 2 variables. There was a significant relationship of muscular strength to BM and FFM in men and women regardless of testing intensity (Table 5). Work capacity was significantly related to FFM in both men (r = 0.35) and women (r = 0.33) in the 65% 1RM group and women in the 90% 1RM group (r = 0.40) but not for men in the 90% 1RM group (r = 0.16).

Table 4: Physical characteristics and pretraining and posttraining performance characteristics of the 65 and 90% 1RM testing groups separated by gender.*†

Table 5: Impact of gender on the relationships between muscular strength (1RM bench press) and selected variables in low-intensity and high-intensity testing groups before and after training.*

Posttraining Performance

The posttraining 1RM bench press and 1RM per kilogram of BM showed significant (p < 0.001) gains in both intensity groups, which caused RepWt and RepWt per kilogram to increase significantly (Table 1). After training, RTF remained unchanged in the 65% 1RM group but decreased significantly in the 90% 1RM group. When tested at 65% 1RM, work capacity increased, whereas it decreased when tested at 90% 1RM. There were no significant differences between intensity groups in the percent change for 1RM, RepWt, RTF, and work capacity (average difference: 16.5–21.4%) (Table 1). Independent of the testing group, women made significantly greater percent gains (average gains = 22.5–24.8%) in 1RM, RepWt, RTF, and work capacity than men (average gains: 13.7–15.8%) (Table 2). Although 90% of the subjects increased 1RM, a greater number of men (85%) and women (75%) in the 65% 1RM testing group made gains in work capacity compared with the 90% 1RM testing group (men = 57% and women = 59%). The correlations between strength gain and work capacity gain for both the 65% 1RM (r = −0.38, p < 0.001) and 90% 1RM (r = −0.40, p < 0.001) groups were negative and significant (Table 5), thus showing a tendency for greater gains in maximal strength to be associated with decreases in work capacity. The correlation between strength gain and work capacity gain for men (r = −0.31, p < 0.001) and women (r = −0.36, p < 0.001) were also significant and negative, revealing no gender-specific difference in the response to training (Table 5). However, across all the groups, the variance accounted for ranged from 8 to 32%, indicating very little dependence of work capacity gain on strength gain.

Prediction Equations

Four curvilinear prediction equations were used to estimate 1RM bench press from RTF in each group (Table 6). At the pretraining evaluation, most of the predicted values for the moderate-intensity testing group were significantly below the actual 1RM, with only the Wathen equation (³⁸) producing nonsignificant differences between predicted and actual 1RM. To the contrary, all of the pretraining predicted values for the high-intensity test group were above the actual 1RM (Table 6). In the pretraining combined analysis of all the subjects, the Lombardi equation (²⁴) produced fewer subjects within ±5% of their actual 1RM (11%) compared with the Desgorces et al. (39%) (¹¹), Mayhew et al. (32%) (²⁵), and Wathen (30%) equations (³⁸). After training, a similar pattern of underprediction in the moderate-intensity testing group and overprediction in the high-intensity testing group was still evident (Table 5). In the posttraining combined sample, the Lombardi (20%) equation (²⁴) still produced fewer subjects within ±5% of their actual 1RM compared with the Desgorces et al. (54%)(¹¹), Mayhew et al. (42%) (²⁵), and Wathen (41%) equations (³⁸).

Table 6: Strength prediction before and after training using repetitions and selected %1RM loads in college-aged men and women.

In the combined analysis of all the subjects, the Desgorces et al. equation (⁷) was the only one to produce accurate estimates of the 1RM at both pretraining and posttraining evaluations and had the smallest 95% confidence interval of percent differences between predicted and actual 1RM (Table 7). The number of subjects within ±5% of the actual 1RM at pretraining was comparable between genders (men = 40%; women = 39%) but was slightly higher for men (58%) than for women (48%) at posttraining. The same pattern was evident for intensity level, with comparable percentage at pretraining (65% 1RM group = 36%; 90% 1RM group = 38%) but a higher value at posttraining for the 90% 1RM group (70%) than for the 65% 1RM group (42%). Standardized beta weights from multiple regression analysis confirmed that gender and intensity level contributed <0.5% each to the estimation of actual 1RM at both the pretraining and posttraining, leaving >99% to be contributed by the predicted 1RM using the Desgorces et al. equation (⁷).

Table 7: Comparison of the difference between predicted and actual strength changes after resistance training in college-aged men and women (n = 147).*

Discussion

By convention, resistance programs using heavier loads (>85% of 1RM) and fewer repetitions (3–6 reps) primarily develop muscular strength, whereas lower loads (<75% 1RM) and higher repetitions emphasize muscular endurance (i.e., RTF) (^22,41). Further, gains in strength are purportedly associated with increased muscular endurance, yet recent studies have reported contrary findings of either no change or reduced RTF after resistance training (^6,7,9,28,33). However, limited research has focused on the effect of heavy resistance programs on muscle work capacity (^3,6,7,33,40). Part of the problem when attempting to assess the effect of training on muscular performance may stem from differences in definition and expression of performance variables. For the present purpose, muscular endurance was defined as the RTF, whereas work capacity was defined by RepWt × RTF (as noted in the Methods section).

Hoeger et al. (¹⁵) indicated that there were no differences in RTF at 40, 60, and 80% between trained and untrained men in the bench press indicating a similar muscular endurance despite differences in training status. However, trained women produced more RTF than did untrained women at the corresponding %1RM indicating increased muscular endurance (¹⁵). Despite that lack of significant difference between trained and untrained men, the former performed 15% more RTFs at 60% 1RM which, in combination with a greater RepWt would have produced 72% greater work capacity than the latter. Similarly, the trained subjects produced 24% more RTFs and would have had an 89% greater work capacity with an 80% 1RM RepWt (¹⁵). Thus, it would appear that the trained individuals had a greater work capacity while expressing a similar muscular endurance.

This study indicates that previously untrained men and women, completing the same heavy resistance program, increased muscular strength but had a varying impact on the expression of muscular endurance (RTF) and work capacity depending upon the intensity of the testing protocol used. In individuals who gained strength, 58% failed to increase work capacity in the 90% 1RM group; however, the same training program significantly enhanced work capacity in 82% of the subjects tested using the 65% 1RM testing protocol. Of those individuals in the 90% 1RM group for whom there was a decrease in work capacity, 55% were men and 45% were women, indicating no gender bias in the effect of the training. Although the differences in RTF (muscular endurance) before and after training for both the 65% 1RM and 90% 1RM groups were minor, the individual differences in RTFs made the biggest contribution to explaining the overall change in work capacity for the 60% 1RM group (94.4%) and the 90% 1RM group (97.2%). This relegated the change in RepWt (3.8 and 0.5%, respectively) and gender (1.8 and 2.3%, respectively) to significantly lesser roles in the changes with training. These findings are noteworthy because the intensity groups were similar in initial strength levels and maximal strength gains made with training. The change in muscular strength was moderately but negatively correlated with change in work capacity, indicating that greater gains in strength in the current subjects were likely to be associated with lesser gains in work capacity. This is in contrast with previous findings in well-trained college football players (⁶) in whom the gains in strength were modestly associated with gains in work capacity for moderate-intensity testing (60–70% 1RM; r = 0.28–0.31) but not for high-intensity testing (80–90% 1RM; r = −0.18 to 0.06). However, what is in agreement between the present and previous studies (^6,7,26,35) is that the RTF (muscle endurance) remained unchanged with training, whereas work capacity increased when tested at moderate-intensity, whereas both RTF and work capacity measured with high-intensity testing tended to decrease after training. Training history may contribute to this because differences in strength (1RM) appear to impact RTF (^6,7,23). Trained and untrained men (²⁶) or low- and high-strength athletes (⁶) performed approximately the same RTFs at 65% 1RM (∼22 RTF), but untrained men (²⁶) and lower-strength athletes (⁶) performed more RTFs at 90% 1RM. Thus, at moderate-intensity, trained or high-strength individuals had a greater work capacity than untrained or low-strength individuals did; however, at high-intensity, the reverse was true, with untrained or low-strength individuals having an equal or greater work capacity. Goto et al. (¹⁴) observed that training with a “hypertrophy/high strength protocol” led to a slight reduction in leg extension work capacity (−4.7 ± 5.8%) compared with training that included a high-repetition set in their program (18.8 ± 9.4%). This trend appears to be supported by a cross-sectional comparison where body builders (typically training with 10–15 repetitions per set) performed more work than the weightlifters (rarely using >3–5 repetitions per set) (¹). Further, when individuals trained with 30–40 repetitions in each of 2 sets (classified as medium resistance, medium repetitions), bench press work capacity (tested at 40% 1RM) increased 22%, whereas individuals performing 6–8 repetitions in each of 3 sets (high resistance, low repetitions) decreased their work capacity by 7% (¹).

In studies in which the same subjects were measured for RTF before and after resistance training (^6,7,26,27), no change in RTF (muscular endurance) was observed; however, increases in RepWt (measured as 60–75% 1RM) produced an improvement in work capacity (ranging from 16 to 33%). In college football players (^6,7), the lack of change in RTF but increase in RepWt after resistance training produced an increase in work capacity only with moderate-intensity testing but a mean decrease in work capacity because of a decrease in RTF with high-intensity testing (>80% 1RM). One of the few studies to produce an increase in RTF at a standard %1RM observed an approximate twofold increase in RTF at 75% of 1RM bench press after 16 weeks of training in national-class, Spanish ball-game players (¹⁶). Interestingly, such increases would have produced an approximately 175% increase in work capacity.

One particularly interesting observation is the apparent reduction in muscular endurance (RTF) and work capacity that is associated with increased strength after training. In studies that have used RTF to represent muscle endurance, some have noted that individuals with greater strength tend to have a lower muscle endurance (^6,7,11,12,33). This is supported by the findings in this study where RTF were poorly related to 1RM at the pretraining and posttraining evaluations for both the 65% 1RM testing group (r = 0.00 and −0.13, respectively) and 90% 1RM testing group (r = −0.19 and −0.21, respectively). Furthermore, 45% of the individuals in the 65% 1RM testing group and 60% of those in the 90% 1RM testing group had decreases in RTF after training, again supporting earlier studies that suggest that heavy-resistance training could hamper muscle endurance (^1,6,7). In studies in which RepWt × RTF has been used to represent work capacity, the findings appear to be more controversial. Observations from this study and others have shown work capacity to increase when measured with a low-to-moderate intensity procedure (^6,7,18) but to decrease with a high-intensity measurement protocol (^6,7,26,28). In the RepWt × RTF protocol, work capacity and 1RM bench press are likely to be positively related, as was the case in this study for the 65% 1RM testing group at the pretraining and posttraining evaluation (r = 0.87 and 0.83, respectively), while the 90% 1RM testing group exhibited a significantly lower relationship (r = 0.51 and 0.50, respectively). Thus, it would appear that understanding the physiological changes in muscle endurance or work capacity after resistance exercise and the expression of those changes hinges on the method used by various investigators to assess and categorize muscular performance. In this study, where initial performance characteristics and the resistance training program were similar, individuals tested using the moderate-intensity protocol showed improvements in work capacity, whereas those tested with the high-intensity protocol showed decrements. This supports previous observations (^6,7,21,26) and the conclusion that increases in muscular strength associated with heavy resistance training programs result in improvements in work capacity expressed with moderate loads (40–70% 1RM) and also result in apparently confounded effects on high-intensity work capacity (loads > 85% of 1RM), which may be unchanged or more likely reduced. Clearly, more work is needed to understand this issue.

The expression of muscular work capacity, using submaximal loads and RTF, is likely determined by an interaction among neural factors, muscle components, and metabolic energy supply (⁵). One possible neural component contributing to increased work capacity could be the desynchronization of motor units resulting in fewer motor units required to complete a given repetitive task, thus offering more rest to parts of the working muscle (²⁹) leading to an increased RTF. In addition, there may be greater neural activation after training to allow increased RTF before fatigue limits performance (¹³). Occurring concurrently with these factors is the possibility that, as muscle contraction intensity increases, muscle force generation becomes sufficient to occlude circulation within the exercising muscle (³⁶), thus potentially hastening the onset of fatigue by limiting energy supply and waste removal and reducing intracontractile metabolic recovery (^5,8,10). However, if training produces increased capillary density in the working muscle, this might reduce the fatigue effect of occluded circulation, thus prolonging contraction (³⁶). Hence, prolonged endurance repetitions may be more related to metabolic factors (i.e., energy supply) (^5,8) than to muscle fiber composition (³⁶) or neural activation as observed with moderate-intensity testing (¹³), but this approach has rarely been studied in repetitive muscular work using external loads (e.g., barbells) as opposed to low-load, long-duration activity (e.g., running). The varying interaction of neural, muscle, and metabolic factors at differing intensities of contraction may make it difficult to pinpoint a limited number of elements controlling work capacity. Because muscular fatigue appears to occur more rapidly at higher intensities, especially with higher levels of strength, further investigations may be required to isolate the major factors along the repetition continuum that dictate work capacity.

This study is one of the few to evaluate the accuracy of prediction methods for tracking the changes in 1RM strength during training (^6,7,26,27). The major concerns when using any prediction technique to estimate muscular strength (1RM) is the degree to which such predictions are able to accurately capture the actual strength performance at any given time in the training cycle and how well prediction techniques can assess changes in strength level. Over a wide range of RTF, curvilinear equations have proven to be better for predicting 1RM (^{6,7,11,24-27,38}) and hence were the main focus in this study.

Interestingly, the best equation for determining 1RM bench press performance both before and after training in this study was formulated on male athletes (⁷). The %1RM range in that study (20–85%) was considerably greater than typically used for predicting 1RM, and yet the correlations between predicted and actual %1RM for the current subjects were very strong at pretraining and posttraining (ICC = 0.912 and 0.947, respectively). This allowed 55% of the women to produce predicted 1RM values within ±2.3 kg of their actual 1RM at pretraining, which was enhanced to 58% after training. In men, 58% were predicted within ±4.5 kg at pretraining and 60% at posttraining. When the intensity groups were analyzed, the high-intensity testing group had a greater percentage of women within ±2.3 kg and men within ±4.5 kg at pretraining (66%) and posttraining (70%) than the moderate-intensity testing group (47 and 49%, respectively). This agrees with earlier work indicating that fewer RTF with greater loads tend to produce better prediction of strength (^6,7,25,27,37). Previous studies have suggested that there is no correlation between RTF and the difference between predicted and actual 1RM (³⁷); however, the current sample had significant correlations between RTF and the difference between predicted and actual 1RM at pretraining (r = 0.43) and posttraining (r = 0.26). These relationships may have been influenced by the design of this study that dichotomized the groups rather than employing a continuous %1RM scale.

The ability of a prediction equation to accurately track changes in muscular strength after training may be critical to the acceptance of the equation for routine use. A unique feature of this study is the comparison of the accuracy of tracking strength changes (i.e., differences between actual strength gains and predicted strength gains) for the 2 intensity groups. The comparison of the measurement of strength changes was not significantly different in the moderate-intensity testing group (actual change = 9.0 ± 6.2 kg; predicted change = 9.2 ± 5.0 kg), whereas the strength change for the high-intensity testing group was significantly underestimated (actual change = 8.3 ± 6.9 kg; predicted change = 6.2 ± 6.0 kg). However, the correlation between predicted and actual changes in strength in the moderate-intensity testing group (ICC = 0.559) was significantly lower than in the high-intensity testing group (ICC = 0.797). In the composite sample, there was no significant difference (p = 0.07) between the actual strength change (8.6 ± 6.6 kg) and the predicted strength change (7.7 ± 5.7 kg), and the correlation between them was strong (ICC = 0.701). Thus, it appears that changes in strength can be tracked with acceptable accuracy over a fairly wide range of intensities using the newly developed Desgorces et al. equation (⁷).

Practical Applications

A primary finding of this study was that heavy-resistance strength training not only improves maximal strength but also has a positive effect on moderate-intensity work capacity. For individuals such as firefighters, police officers, maintenance workers, and lumberjacks whose daily tasks require repetitive work at <70% of their maximum strength capacity, an increase in maximal strength is likely to transfer to greater work output. In this study, moderate-intensity work capacity was determined at 65% of 1RM, which meant that the RepWt increased as the individual got stronger. In an industrial setting where the load might remain constant, the additional strength would mean that the RepWt would represent a decreasing percent of maximal strength and hence should become easier to manipulate as more strength is gained.

A secondary finding of this study was that an RTF approach can be used to estimate 1RM strength in the bench press and can be used to track changes resulting from a training program in young, untrained men and women. This approach could save time in the testing process, allow individuals to periodically check their training progress, and offer motivation for training adherence. Previous sources have indicated that the best prediction (i.e., minimal error) will be achieved when the equation used is matched to the training status (level of muscular strength), training goal of the cycle, and the general training base of the individual. The current work expands those concepts for application to young men and women who have relatively little background in resistance training. In the present context, adequate predictions with ≤5% error can be realized using a wide range of RTFs by employing a curvilinear equation.