Secondary Logo

Journal Logo

Original Research

The Effects of Manual Resistance Training on Improving Muscular Strength and Endurance

Dorgo, Sandor1; King, George A1; Rice, Christopher A2

Author Information
Journal of Strength and Conditioning Research: January 2009 - Volume 23 - Issue 1 - p 293-303
doi: 10.1519/JSC.0b013e318183a09c
  • Free

Abstract

Introduction

Improving muscular strength and endurance has long been the goal of physical training programs. To elicit changes in muscular strength and endurance, skeletal muscles must receive appropriate levels of stress, commonly achieved by the application of external resistance. Some of the most widely accepted methods for applying exercise resistance are free weights, weight machines, and elastic cords. Some less common methods include hydraulic machines, pneumatic machines, stones, kegs, and logs. Manual resistance training (MRT) is another method that has yet to be well accepted among strength and conditioning professionals. A possible explanation for the underutilization of MRT may be the lack of published research investigating the efficacy of this very basic and simple training method.

It is well accepted that many free weight training exercises do not apply equal resistance to the contracting muscle throughout the movement because of joint position leverage and susceptibility of the static load to gravity (i.e., the resistive load is greatest when the movement is perpendicular to the ground and in direct line with gravitational forces). Accommodating resistance is a term used to describe a work load that varies during an exercise movement to match the force-producing ability of the target muscle group throughout the full range of motion (5,12,21,26); it is commonly associated with isokinetic dynamometers and exercise machines designed with a variable-resistance cam. Previous investigators have speculated that exercises that elicit maximal muscle contraction throughout the full range of motion may produce greater strength gains than constant-load resistance (8,12,21). Manual resistance training incorporates accommodating resistance concepts; thus, in theory, it may generate muscular strength improvements similar to traditional weight resistance training (WRT).

Publications on MRT date back to the early 1980s and come mainly from practitioners' journals (1,10,16,25,27). Other terms used for the same training concept of MRT are manual accommodating resistance exercises (1) and cooperative strength training (25). With the application of MRT, participants work in pairs, with one assuming the role of the lifter and the other being the spotter. The resistance for any given exercise is provided by the spotter, and thus traditional weight training equipment, such as bars, dumbbells, and plates are not used. Most traditional free weight and machine-based resistance training exercises can be simulated (16) when MRT exercises are properly designed and may provide the intended training stimuli. However, MRT is not appropriate to mimic explosive movements (i.e., those used in Olympic weightlifting), because the resistance provided by a spotter may not match the force curves generated in these activities. To establish an effective training position or exercise set-up for MRT, only limited equipment is necessary, which may include benches, chairs, tables, step boxes, PVC pipes, and straps. The most ideal training position for any MRT exercise provides the spotter with the mechanical advantage, thus allowing the spotter to intentionally control the resistance applied for the lifter. Consequently, a maximal effort and muscular contraction may be elicited from the lifter throughout the full range of motion, which is known to be available only through isokinetic machines (1). Thus, in theory, MRT could provide significant muscular strength improvements (1). Nevertheless, research is limited regarding the MRT training concept.

One study examining the effects of MRT had 1100 male soldiers train for 12 weeks by either MRT or calisthenics (11). The study's findings indicate that MRT was more effective than calisthenics in increasing strength as measured by a hand-grip dynamometer, medicine ball throws, and the number of push-ups performed in 2 minutes (11). In another study (19), improvements in strength and endurance for a group of untrained women that completed a 6-month training program comprising plyometric, calisthenics, and MRT were compared with improvements for a traditional resistance training group and an aerobic training group. Manual resistance training was used to mimic the field training program most often used by soldiers without access to equipped training facilities. The authors report the greatest improvement in bench press and squat strength for the equipment-based traditional resistance training group; however, the group using MRT exercises also showed moderate strength improvements during the initial stages of the program (19). This study, although not applying a pure MRT program compared with WRT, concluded that traditional resistance training was clearly superior for improving strength and endurance (19).

Although a deficiency of the MRT method is the inability to quantify the resistance applied by the spotter whereas, with traditional resistance training, the intensity of the movement is indicated by the amount of weight lifted, numerous advantages over traditional resistance training exist and have been reported previously (1,10,16,25,27). Perhaps the greatest advantage of MRT is the minimal need for equipment, which makes it possible for low-budget athletic programs, public recreational centers, and schools to apply resistance training if a well-equipped weight facility is not available. The physiologically significant advantage of MRT is the variable resistance, which potentially allows for maximum muscular tension throughout the full range of motion of a given exercise, and maximum effort in every repetition of a given set. For example, a set of 10 repetitions, if performed properly, is composed of 10 maximum-effort repetitions where the spotter provides less resistance as the lifter fatigues. Theoretically, this maximum overload provided by the spotter results in maximum muscular involvement (16) and is effective in gaining strength (1). Therefore, the purpose of this study was to investigate the effects of an MRT program on muscular strength and muscular endurance, and to compare these results with the outcome of an identically structured WRT program.

Methods

Experimental Approach to the Problem

The experimental design included a longitudinal training intervention in which changes in muscular strength and muscular endurance were assessed in response to two different types of resistance training programs. To compare the effectiveness of MRT with that of WRT, 84 healthy college students were randomly assigned to either an MRT or WRT group and engaged in a 14-week training program. Each participant's performance was assessed before and immediately after the 14-week training period. Muscular strength in the upper body was assessed by the one-repetition maximum (1RM) bench press test, and the 1RM squat test assessed lower-body strength. Muscular endurance tests were performed with 70% load of the achieved pretraining 1RM weight for both the bench press and squat exercises.

Subjects

Eighty-four (N = 84) undergraduate students were recruited for this study: 46 males and 38 females. After the pretraining assessment of muscular strength and muscular endurance, participants were randomly assigned to either the MRT (n = 53) or the WRT (n = 31) group. The ratio of males to females was similar for the MRT and WRT groups (53 to 47% and 58 to 42%, respectively). Because of space, equipment, and scheduling issues, the number of participants in the WRT group was limited. Pretraining descriptive characteristics of the subjects are presented in Table 1.

Table 1
Table 1:
Mean (±SD) pretraining descriptive characteristics of the weight resistance training (WRT) group and the manual resistance training (MRT) group study participants.

Before the data collection, each participant completed a health history and training background questionnaire to assess participants' health, physical limitations, physical activity habits, and resistance training experiences. All participants reported being healthy and suitable for participation in a resistance training program. Forty-two subjects reported performing vigorous physical activity for a minimum of 1 hour twice per week, and 38 subjects reported engaging in resistance training a minimum of 2 hours per week before the intervention. The project was approved by the appropriate institutional review board, and each subject provided written informed consent to participate. Before the experiment, the complete testing procedure and training protocol were thoroughly explained to each subject both orally and written in the consent form.

Muscular Strength and Muscular Endurance Assessment Procedures

Subjects were first tested on their 1RM bench press and squat performance. Before the 1RM testing, all participants followed a standard warm-up routine composed of one set of 10 repetitions with approximately 50% of the anticipated 1RM load, followed by 3-5 repetitions with approximately 75% of the 1RM. After the warm-up protocol, subjects performed their first 1RM attempt with a load slightly lower than their anticipated maximum weight. Trained research assistants supervised the testing and dictated the resistance of each 1RM attempt. A minimum rest interval of 5 minutes was strictly enforced between 1RM attempts. Most subjects achieved their true 1RM weight within three to four attempts.

Each subject's muscular endurance was assessed 24-48 hours after the muscular strength test. The muscular endurance tests were performed with 70% of the achieved 1RM weight for both the bench press and squat exercises. After a warm-up routine composed of a light cardiovascular activity and light weight lifting on the two exercises, subjects performed the maximum number of repetitions to exhaustion with the predetermined weight. Trained research assistants monitored form and technique, and only correctly executed repetitions were counted. Posttraining 1RM testing procedures followed the same warm-up and testing protocol. To accurately measure improvements in muscular endurance, the load for the posttraining test was the same load as the pretraining test (70% of the pretraining 1RM load).

Training Protocol

All participants, independent of pretraining performance, performed the same workout routine. However, the absolute resistance applied for a given exercise was individualized. Participants engaged in a 14-week training program with three 1-hour training sessions per week. All participants were instructed to abstain from other strength training activities during the study period. All sessions were organized in a triset (mini-circuit) training format, where three exercises were performed in succession with short (20-30 seconds) rest intervals between each exercise. The volume and intensity of the training sessions were adjusted weekly according to the training plan, which was designed by applying the progressive overload principle. Subjects performed a total of 15 sets per training session at the beginning of the program, which was then progressively increased to 28 sets by the last weeks of the intervention. Generally, participants performed six to nine large-muscle-group exercises during each training session (two or three trisets) with two to four sets of 8-12 repetitions. All subjects were required to rest for at least 24 hours between training sessions. A sample program plan is presented in Table 2.

Table 2
Table 2:
Sample training program for weight resistance training (WRT) group and manual resistance training (MRT) groups.

The training intensity was kept in the hypertrophy zone (8-12RM) for the entire training program because working at these intensity levels was perceived to provide sufficient stimuli for simultaneous improvements in muscular strength and muscular endurance. At the beginning of the program, sets of 12 repetitions were used, but for the majority of the 14-week intervention subjects performed all exercises with 10 repetitions. In the last few weeks of the program, as the total number of sets performed per training session reached the maximum 28 sets, the number of repetitions performed per set was reduced to eight. Participants in the WRT group were encouraged to use sufficiently heavy loads to reach full exhaustion in each set (i.e., performing 10 repetitions with 10RM load). Trained research assistants supervised all training sessions, monitoring participants for safety and motivational purposes. Spotters in the MRT group were instructed to provide maximum resistance for their partners adjusted to the lifter's level of fatigue while allowing for full range of motion and smooth execution of the movement in each repetition. The speed of movements for the MRT exercises were controlled (approximately 3 seconds for both eccentric and concentric phases of each movement), which assisted MRT spotters with applying the appropriate resistance. The trained research assistants that supervised the MRT group were also responsible for monitoring exercise techniques and encouraging the lifters and the spotters for greater effort.

The training programs for the two groups were as identical as possible. Both groups performed the same number of exercises with the same numbers of sets and repetitions. The rest intervals between exercises and sets were also identical. The researchers attempted to create a training program in which the MRT and WRT exercises in the two programs were as similar as possible. However, because the force curve differs between the variable resistance applied during MRT and the constant resistance of WRT for a given movement, exercises in the MRT and WRT programs were not biomechanically identical. The WRT program was primarily based on free weight large-muscle-group multijoint exercises (i.e., bench press, shoulder press, squat, lunge, etc.), with single-joint movements (i.e., leg curl, arm curl, etc.) only used as supplemental exercises. For most exercises, the MRT exercise mimicked the WRT exercise by targeting the same muscle groups, requiring identical movements, and using similar exercise set-ups. For a few WRT exercises, however, a similar set-up for the MRT version was not practical for providing the spotter with the mechanical advantage, and, therefore, the training stimulus was not sufficient. For these few instances, an exercise that targeted the same muscle group and with a similar movement was applied.

A simple example for identical WRT and MRT movement is the standing biceps curl (Figure 1). Whereas subjects in the WRT group performed this exercise with a standard weight bar, MRT group participants used a PVC pipe with the resistance provided by their partners. Here, the lifter assumed the appropriate lifting position for the exercise with the PVC pipe while the spotter kneeled in front of the lifter with his or her hands on the pipe. As the lifter performed flexion of the elbows, the spotter resisted the movement so that the movement would be smooth and continuous. In the eccentric phase of the movement, the spotter applied more force and pulled the pipe down in a controlled manner while the lifter attempted to resist and slow down the descent of the pipe. Spotters were constantly supervised for providing proper resistance, with the speed of the movement being the best indicator. This partially ensured that the lifters worked with the highest intensity for the given exercise and set. However, because of the nature of MRT, no quantifiable feedback was available for the MRT subjects on the exercise intensity, as opposed to the known amount of weight lifted for the WRT subjects.

Figure 1
Figure 1:
Manual resistance training standing biceps curl exercise demonstrated by two subjects.

In addition to closely mimicking the WRT exercises, a priority when designing MRT exercises was to provide the spotter with a mechanical advantage over the lifter for any given exercise. The spotter's ability to generate greater forces than the lifter, thus controlling the applied resistance throughout the range of motion, is critical when applying MRT. This may be achieved by using exercise set-ups where the spotter can use larger muscle groups or the entire body weight to overcome the forces that the lifter may generate in the targeted muscle groups. With such an exercise set-up, a weaker spotter is able to provide sufficient resistance for a stronger lifter, enabling individuals of differing strength to be partners. An example of an exercise set-up where the spotter has the mechanical advantage is illustrated in Figure 2.

Figure 2
Figure 2:
Resisted seated chest press. The spotter (female) has a mechanical advantage over the lifter (male) because she is able to utilize both upper- and lower-body muscle groups to apply resistance.

The resisted seated chest press exercise was one of the primary MRT exercises applied in the present study to mimic the free weight bench press used by the WRT group. In the illustrated exercise set-up (Figure 2) the noticeably weaker female subject (BW = 54.4 kg, 1RM bench press = 36.3 kg) was able to provide sufficient resistance for the stronger male subject (BW = 106.6 kg, 1RM bench press = 136.1 kg). Specifically, by attaching a 2000-N-capacity hanging scale to the support chain, we were able to measure the concentric force generated during the seated chest press exercise. The male subject shown in Figure 2 was able to generate 1343 N of concentric force while in the lifter position, whereas the female subject was able to generate 1423 N of concentric force from the spotter position. Although we were not able to measure maximum eccentric strength, it is reasonable to assume that the female spotter may have been able to generate even greater eccentric forces. Consequently, the exercise set-up provided the weaker spotter a mechanical advantage enabling her to generate more than sufficient resistance to elicit maximum muscular contraction from the stronger lifter (Figure 2).

Statistical Analyses

All statistical analyses were performed using a software package (SPSS for Windows, version 13.0; SPSS, Inc., Chicago, Ill). Pre- and posttraining data were analyzed for main effects using a two-way analysis of variance. When significant main effects were revealed, specific differences were assessed using Bonferroni adjusted t-tests. One-repetition maximum was defined as the greatest weight moved through the full range of motion (one repetition) for the bench press and squat exercises. Absolute performance was defined as the actual total weight (kg) lifted during the 1RM test. Relative performance was defined as the absolute 1RM weight divided by body mass (kg·kg−1 body mass). Muscular endurance performance was recorded as the maximum number of repetitions completed with 70% of pretraining (baseline) 1RM load. Alpha was set at the 0.05 level.

Results

At baseline, there was no significant difference between the MRT and WRT groups in the absolute and relative strength measures for either the bench press (p > 0.36) or the squat test (p > 0.61). Similarly, there were no significant differences between groups for baseline muscular endurance values of the bench press (p > 0.64) or the squat exercise (p > 0.46). However, a significant effect of sex (p < 0.001) was observed for both baseline and posttraining values where males were significantly stronger than females.

Compared with baseline values, the 14-week training programs produced significant improvements in muscular strength (p < 0.001) for both training groups (Table 3). For the WRT group, there was a significant (p < 0.001) improvement in the absolute 1RM bench press performance, from 67.3 ± 33.2 kg at baseline to 73.9 ± 31.8 kg after training; and in the relative 1RM bench press performance, from 0.88 ± 0.38 kg·kg−1 body mass to 0.96 ± 0.36 kg·kg−1 body mass, respectively. From baseline to posttraining, significant improvements (p < 0.001) in performance were also observed in the MRT group for absolute bench press strength (61.6 ± 34.3 to 66.1 ± 32.4 kg, respectively) and relative bench press strength (0.80 ± 0.37 to 0.87 ± 0.34 kg·kg−1 body mass, respectively). For squat performance after 14 weeks of training compared with baseline, there was a significant (p < 0.001) improvement in absolute strength and relative strength for the WRT group (81.1 ± 35.8 to 107.8 ± 35.5 kg, and 1.07 ± 0.38 to 1.42 ± 0.36 kg·kg−1 body mass, respectively) and for the MRT group (76.7 ± 38.6 to 97.2 ± 39.3 kg, and 1.02 ± 0.43 to 1.30 ± 0.41 kg·kg−1 body mass, respectively). No significant differences in absolute or relative muscular strength of the bench press or squat were observed between the WRT and MRT groups after the 14-week training program (p > 0.22).

Table 3
Table 3:
Mean (±SD) absolute and relative muscular strength values at baseline and after the 14-week training program, and absolute and relative change in muscular strength for the weight resistance training (WRT) group and the manual resistance training (MRT) group.

The 14-week training program facilitated significant (p < 0.001) muscular endurance improvements after training compared with baseline for the WRT and MRT groups (Table 4). Muscular endurance values of the WRT group significantly improved from 13.5 ± 4.0 repetitions at baseline to 21.2 ± 6.6 repetitions after training for the bench press (p < 0.001), and squat muscular endurance significantly improved from 17.1 ± 10.6 repetitions at baseline to 39.3 ± 17.6 repetitions after training (p < 0.001). For the MRT group, muscular endurance improved significantly (p < 0.001) for the bench press from 14.0 ± 4.4 repetitions at baseline to 20.0 ± 7.3 repetitions after training, and from 15.4 ± 9.4 repetitions at baseline to 32.4 ± 14.0 repetitions after training for the squat. No significant differences in muscular endurance were observed between the WRT and MRT groups after the 14-week training program for the bench press (p > 0.53) or the squat (p > 0.09) exercises.

Table 4
Table 4:
Mean (±SD) muscular endurance values at baseline and after the 14-week training program, and absolute and relative change in muscular endurance for the weight resistance training (WRT) group and the manual resistance training (MRT) group.

Discussion

The purpose of this study was to investigate the effects of an MRT program on bench press and squat strength and muscular endurance, and to compare these results with the outcome of an identically structured WRT program. All MRT and WRT training sessions were organized in a triset format where three exercises were performed consecutively, similar to circuit training. Two to four sets of 8-12 repetitions were performed for all exercises in both programs. The major findings of this study were that improvements in muscular strength and muscular endurance after a 14-week MRT program were similar to those produced by a WRT program, and well-designed MRT exercises seemed to be effective in improving muscular fitness.

The scientific literature contains numerous investigations of weight-based resistance training programs; however, there exists a relative paucity of published reports focused on MRT. Considering the similar results between the WRT and MRT groups of the current study, a comparison of the WRT group with previously reported weight-based resistance training programs seems appropriate for evaluating the overall effectiveness of our WRT and MRT programs. The strength improvements for the WRT group of the present study are comparable with those previously reported. Table 5 provides a summary of previously reported resistance training studies that used the bench press to assess upper-body strength and the squat or leg press to assess lower-body strength. The studies presented in Table 5 also implemented training methods similar to those used for the WRT group of our study (i.e., free weights and/or exercise machines, moderate training intensity, 8-20 repetitions, two to four sessions per week, 8- to 24-week duration). Bench press strength improvements for these previous studies ranged from 1.8% (18) to 31.9% (17), whereas improvements for the squat and leg press strength were between 5.2% (18) and 53.5% (17). However, the majority of investigations involving an 8- to 12-week, moderate-intensity resistance training program reported 12.4 to 20.4% improvement for the bench press (2,3,4,6,9,20, 32) and 11.2 to 33.0% improvement for the squat or leg press strength (3,5,6,9,23,26,28,32). Comparable with the reported literature, the bench press and squat strength improvements of the WRT group in the present study were 9.8 and 32.9%, respectively. Additionally, our finding that the degree of improvement for upper-body strength was not as great as that of the lower body is in agreement with previous research (3,28,33,35).

Table 5
Table 5:
Summary of resistance training research that assessed upper-body strength by bench press and lower-body strength by squat or leg press.

Our results for the strength improvement of the WRT group were also similar to findings of previous studies using a circuit training format. Scheduling restrictions for the training sessions of the WRT and MRT groups necessitated a time-efficient training format. The triset (mini-circuit) training format was selected because we hypothesized that this training format was appropriate to achieve simultaneous improvements in muscular strength and endurance while reducing the amount of time spent off-task. Previous research has demonstrated that, for untrained individuals, circuit training and traditional weight training programs are similarly effective for eliciting improvements in strength, although high-intensity weight training is the most optimal for substantial strength increases both for trained and untrained subjects (13). Most previous studies that were methodologically similar to the present study and that used a circuit training method to improve upper- and lower-body strength reported 12.2-21.0% improvement for bench press strength (14,15,22-24,36) and 16.0-27.0% improvement for leg press strength (15,24,36). The similar improvements for muscular strength (bench press: 9.8%; squat: 32.9%) of our WRT group to those of previous reports demonstrates the effectiveness of our training program and supports the comparison with our MRT group.

The muscular endurance improvements of our WRT group (Table 4) far exceeded those improvements reported in previous studies (Table 6). Previous research had assessed muscular endurance using resistance loads of 45-80% of pretraining (baseline) 1RM (23,32). For this study, muscular endurance for the bench press and squat exercises was assessed by recording the maximum number of repetitions performed by each subject with a resistance equal to 70% of the baseline 1RM. Bench press endurance of our WRT group improved 57.8%, as opposed to the 2.1-24.8% improvements previously reported for studies using similar training and testing protocols (2,23,32). Similarly, our subjects' 129.2% improvement for squat endurance was greater than the 16.0-65.9% improvements previously reported for squat or leg press endurance (23,32). Whereas the differences in bench press and squat endurance between our findings and those of previous studies are impressive, a remarkable 54-152% improvement in muscular endurance has been reported for single-joint exercises (7). These data suggest that our training program facilitated improvements in muscular endurance at the higher end of the performance spectrum compared with previous reports that similarly assessed upper- and lower-body muscular endurance (23,32). However, it is important to acknowledge that not all subjects in the present study had at least a moderate level of resistance training experience before the intervention, and thus an exercise learning effect may have contributed to the increased performance in addition to the improved muscle function.

Table 6
Table 6:
Summaries of reported muscular endurance improvements of studies using bench press to assess upper-body strength and squat or leg press to assess lower-body strength.

To our knowledge, the effectiveness of a training program that exclusively used MRT exercises has not been investigated. However, the limited available literature on manual training suggests that the effects of manual training are similar to those of accommodating resistance training because maximal muscle tensions may be elicited for the full range of motion of a given exercise (1). Accommodating resistance training devices, such as variable-resistance cam designs and isokinetic machines, vary the applied resistance during the movement in an attempt to match the force-producing ability of the given musculoskeletal lever system for the full range of motion (5,12,21,26). It has been hypothesized that training with maximal muscle contractions elicited throughout the full range of motion may result in superior strength gains compared with those achieved by training with constant resistance (8,12,21). Our MRT exercises required the resistance to be applied by a partner (spotter), and, because a skilled spotter may be able to vary the applied resistance to elicit a maximal muscular effort from the lifter throughout the full movement, MRT exercises may become a more accepted form of accommodating resistance. Consequently, the accommodating nature of the resistance applied with MRT may provide a similar or even greater level of improvement in strength than that achieved by traditional WRT.

To overcome the lack of available data on MRT, we hypothesized that studies investigating the effects of accommodating resistance training, using variable-resistance cam designs and isokinetic machines, would provide a legitimate basis for comparison. We identified several investigations that used accommodating resistance training for similar training periods (6-20 weeks) and that assessed upper-body strength by the 1RM bench press and lower-body strength by the 1RM squat or leg press exercises (Table 7). These previous reports indicate that an 8- to 20-week accommodating resistance training program generated bench press strength improvements of 9.7-18.0% (4,5), 3.1-4.5% improvements for squat strength (34), and 6.7-11.2% improvements for leg press strength (5,14,26,29).

Table 7
Table 7:
Summaries of reported strength gains elicited by variable-resistance or isokinetic training programs that used isotonic bench press to assess upper-body strength and isotonic squat or leg press to assess lower-body strength.

In the present study, as a result of the 14-week MRT program, subjects demonstrated a 7.4% improvement in bench press strength, which was similar to that observed for circuit training (2.1-24.8%) (2,23,32). However, the bench press strength improvement for our MRT group was slightly lower than the 9.7-18.0% strength improvements reported in previous accommodating resistance training studies (4,5) and the 11.8-20.4% improvement reported for traditional WRT programs (2-4,6,9,20,32). Conversely, the 26.8% squat strength improvement for our MRT group was greater than the 6.7-11.2% improvement reported by previous accommodating resistance training studies (5,14,26,29,34) and was comparable with previous studies of traditional resistance training (11.2-34.5% improvement) (3,5,6,9,23,26,28,32) and circuit training programs (16.0-27.0% improvement) (15,24,36). Similar to the WRT group, the MRT group's muscular endurance improvements of 43.1% for the bench press and 109.8% for the squat exceed the greatest improvements previously reported (24.8 and 65.9%, respectively) (32). Although the changes in strength and muscular endurance were significant for both the MRT and WRT groups, we must acknowledge that the performance improvements may be partially attributed to neuromuscular adaptations and exercise learning effects. Approximately half of our subjects were not involved in regular resistance training programs before the intervention, and thus it is likely that these subjects experienced some level of neuromuscular adaptation. However, noticeable improvements in strength and endurance were also observed in those MRT and WRT subjects who had participated in regular resistance training programs before the intervention. Nevertheless, because the physiological parameters of subjects in the MRT and WRT groups were similar, and the MRT and WRT programs produced similar improvements in muscular strength and endurance, it is reasonable to assume that subjects in both groups received similar training stimuli throughout the 14-week experimental period.

It is well recognized in the literature that measured strength improvements may not accurately represent actual strength gains when the assessment method or device is different from that used during the training program. The theory that measured improvements in strength are greatest when assessed with a device or procedure similar to the training procedure is often termed movement pattern or training-testing specificity and has been repeatedly observed in previous studies (5,14,21,26,29,30-34). Therefore, strength improvements elicited by accommodating resistance training may not seem as great if measured by an exercise that is different than those used in the program (i.e., free weight 1RM measure). This must be acknowledged when interpreting the results of the present study because a standardized strength measure (free weight 1RM) was used for both the WRT and MRT groups. The WRT group had an apparent advantage in the free weight 1RM testing because the same equipment was used for training and assessment, whereas the MRT group did not use any free weights or exercise machines during the 14-week program. Therefore, it may be inferred that the slightly greater strength improvements observed for the WRT group compared with the MRT group are attributable to training-testing specificity rather than differences in the effectiveness of the training modalities.

These data suggest that a short-term, well-designed MRT program can elicit improvements in muscular strength and muscular endurance similar to traditional weight training, circuit training, and accommodating resistance training programs. However, the long-term applicability and effectiveness of the MRT modality require further investigation. For example, will the application of an MRT program be effective for individuals with extensive experience with traditional resistance training modalities (advanced resistance trainees) such as athletes or those who have already experienced substantial neuromuscular adaptations? What is unique to the MRT exercises designed for this study is that within a given exercise set, the applied resistance can be varied throughout the movement of a single repetition and between repetitions. This enables the lifter to produce a maximal muscular effort throughout the full range of motion with each repetition of the set. Well-designed MRT exercise positions provide the spotter a mechanical advantage enabling a weaker spotter to generate sufficient resistance to elicit maximum muscular contraction from the lifter; however, a disadvantage of the MRT modality is that no direct training intensity feedback is available for the lifter. Whereas in traditional resistance training the exercise intensity is reflected by the amount of weight lifted, in MRT only the application of a force-measuring device would provide the lifter with accurate intensity values. In addition, because the resistance is provided by a partner, another disadvantage of MRT is that the effectiveness of this modality greatly depends on the spotter's ability to provide appropriate resistance while simultaneously allowing for the full range of motion. To achieve this balance between the applied resistance and the range of motion, spotters may require more extensive training than in traditional resistance training programs. Nevertheless, if the lifter and spotter can work together appropriately, the advantages of MRT, including the minimal and relatively inexpensive equipment, make this modality a practical and useful alternative resistance training method.

Practical Applications

The results of the present study suggest that MRT is effective for improving muscular strength and muscular endurance. Strength and conditioning professionals may benefit from the application of MRT because it provides a cost-effective alternative training method for poorly equipped facilities or a supplemental training method to conventional weight-based resistance training. The application of MRT may be particularly appropriate in non-weight-room-based training settings, including indoor (classrooms, gymnasiums, etc.) or outdoor (field) environments. Manual resistance training also requires little space and may be performed in areas otherwise not suitable for resistance training. Because the effectiveness of the MRT method is dependent on the lifter-spotter partnership and maximum effort, as well as the proper exercise set-up that provides the spotter with mechanical advantage, professionals applying this training modality need to teach their athletes the correct MRT lifting and spotting techniques before allowing the exertion of maximum force.

Acknowledgments

This study was funded by the University Research Institute at the University of Texas at El Paso.

References

1. Adamovich, DR and Seidman, SR. Strength training using MARES (manual accommodating resistance exercises). Natl Strength Cond Assoc J 9: 57-59, 1987.
2. Anderson, T and Kearney, JT. Effects of three resistance training programs on muscular strength and absolute and relative endurance. Res Q Exerc Sport 53: 1-7, 1982.
3. Baker, D, Wilson, G, and Carlyon, R. Periodization: the effects on strength of manipulating volume and intensity. J Strength Cond Res 8: 235-242, 1994.
4. Berger, RA and Hardage, B. Effect of maximum loads for each of ten repetitions on strength improvement. Res Q 38: 715-718, 1967.
5. Boyer, BT. A comparison of the effects of three strength training programs on women. J Appl Sport Sci Res 4: 88-94, 1990.
6. Brazell-Roberts, JV and Thomas, LE. Effects of weight training frequency on the self-concept of college females. J Appl Sport Sci Res 3: 40-43, 1989.
7. Butts, NK and Price, S. Effects of a 12-week weight training program on the body composition of women over 30 years of age. J Strength Cond Res 8: 265-269, 1994.
8. Cabell, L and Zebras, CJ. Resistive torque validation of the Nautilus multi-biceps machine. J Strength Cond Res 13: 20-23, 1999.
9. Coleman, AE. Nautilus vs universal gym strength training in adult males. Am Correct Ther J 31: 103-107, 1977.
10. Diange, J. Manual resistance exercises: incorporated during both the in-season and off-season, this program will help athletes develop and maintain strength. Athl J 62: 14-19, 1982.
11. Dombroski, RT and Henderson, JM. Partner resistance exercises versus calisthenics for upper body strength improvement. In: Third Annual Meeting of American Medical Society of Sports Medicine. Ranch Mirage, Calif: American Medical Society of Sports Medicine, 1994.
12. Fleck, SJ and Kraemer, WJ. Designing Resistance Training Programs. Champaign: Human Kinetics, 2004.
13. Gettman, L and Pollock, M. Circuit weight training: a critical review of its physiological benefits. Phys Sportsmed 9: 44-60, 1981.
14. Gettman, LR, Culter, LA, and Strathman, TA. Physiologic changes after 20 weeks of isotonic vs isokinetic circuit training. J Sports Med Phys Fitness 20: 265-274, 1980.
15. Gettman, LR, Ward, P, and Hagan, RD. A comparison of combined running and weight training with circuit weight training. Med Sci Sports Exerc 14: 229-234, 1982.
16. Hendrick, A. Manual resistance training for football athletes at the U.S. Air Force Academy. Strength Cond J 21(1): 6-10, 1999.
17. Herrick, AB and Stone, WJ. The effects of periodization versus progressive resistance exercise on upper and lower body strength in women. J Strength Cond Res 10: 72-76, 1996.
18. Hoffman, JR, Kraemer, WJ, Fry, AC, Deschenes, M, and Kemp, M. The effects of self-selection for frequency of training in winter conditioning program for football. J Appl Sport Sci Res 4: 76-82, 1990.
19. Kraemer, WJ, Mazzetti, SA, Nindl, BC, Gotshalk, LA, Volek, JS, Bush, JA, Marx, JO, Dohi, K, Gomez, AL, Miles, M, Fleck, SJ, Newton, RU, and Hakkinen, K. Effect of resistance training on women's strength/power and occupational performances. Med Sci Sports Exerc 33: 1011-1025, 2001.
20. Lee, A, Craig, BW, Lucas, J, Pohlman, R, and Stelling, H. The effect of endurance training, weight training and a combination of endurance and weight training on blood lipid profiles of young male subjects. J Appl Sport Sci Res 4: 68-75, 1990.
21. Manning, RJ, Graves, JE, Carpenter, DM, Leggett, SH, and Pollock, ML. Constant vs. variable resistance knee extension training. Med Sci Sports Exerc 22: 370-375, 1990.
22. Marcinik, EJ, Potts, J, Schlabach, G, Will, S, Dawson, P, and Hurley, BF. Effects of strength training on lactate threshold and endurance performance. Med Sci Sports Exerc 23: 739-743, 1991.
23. Marx, JO, Ratamess, NA, Nindl, BC, Gotshalk, LA, Volek, JS, Dohi, K, Bush, JA, Gomez, AL, Mazzetti, SA, Fleck, SJ, Hakkinen, K, Newton, RU, and Kraemer, WJ. Low-volume circuit versus high-volume periodized resistance training in women. Med Sci Sports Exerc 33: 635-643, 2001.
24. Mosher, PE, Underwood, SA, Ferguson, MA, and Arnold, RO. Effects of 12 weeks of aerobic circuit training on aeroic capacity, muscular strength, and body composition in college-age women. J Strength Cond Res 8: 144-148, 1994.
25. Munson, WW and Pettigrew, FE. Cooperative strength training: a method for preadolescents. J Phys Educ 59: 61-66, 1988.
26. Pipes, TV. Variable resistance versus constant resistance strength training in adult males. Eur J Appl Physiol Occup Physiol 39: 27-35, 1978.
27. Riley, DB. Manual resistance: a productive alternative (part 1). Scholast Coach 51: 80-86, 1981.
28. Schiotz, MK, Potteiger, JA, Huntsinger, PG, and Denmark, DC. The short-term effects of periodized and constant-intensity training on body composition, strength, and performance. J Strength Cond Res 12: 173-178, 1998.
29. Smith, MJ and Melton, P. Isokinetic versus isotonic variable-resistance training. Am J Sports Med 9: 275-279, 1981.
30. Stanforth, PR, Painter, TL, and Wilmore, JH. Alteration in concentric strength consequent to powercise and universal gym circuit training. J Appl Sport Sci Res 6: 152-157, 1992.
31. Stone, MH, Collins, D, Plisk, S, Haff, G, and Stone, ME. Training principles: evaluation of modes and methods of resistance training. Strength Cond J 22(3): 65-76, 2000.
32. Stone, WJ and Coulter, SP. Strength/endurance effects from three resistance training protocols with women. J Strength Cond Res 8: 231-234, 1994.
33. Stowers, T, McMillan, J, Scala, D, Davis, V, Wilson, D, and Stone, M. The short-term effects of three different strength-power training methods. Natl Strength Cond Assoc J 5: 24-27, 1983.
34. Wathen, D and Shutes, M. A comparison of the effects of selected isotonic and isokinetic exercises, modalities, and programs on the acquisition of strength and power in collegiate football players. Natl Strength Cond Assoc J 4: 40-42, 1982.
35. Willoughby, DS. The effects of mesocycle-length weight training programs involving periodization and partially equated volumes on upper and lower body strength. J Strength Cond Res 7: 2-8, 1993.
36. Wilmore, JH, Parr, RB, Girandola, RN, Ward, P, Vodak, PA, Barstow, TJ, Pipes, TV, Romero, GT, and Leslie, P. Physiological alterations consequent to circuit weight training. Med Sci Sports 10: 79-84, 1978.
Keywords:

accommodating resistance training; weight training; resistance training modalities; circuit training

© 2009 National Strength and Conditioning Association