Strength training has been recognized by the American College of Sports Medicine (ACSM), American Heart Association and the Surgeon General as a key component of physical fitness programs (18). Not only has strength training become an integral part of athletic conditioning and personal physical enhancement, but it is also needed to maintain one's quality and quantity of life (21).
Strength and Conditioning Specialists, personal trainers, and fitness professionals prescribe resistance-training programs based on a percentage of an individual's 1-repetition maximum (1RM). The 1RM is considered the “gold standard” of dynamic strength testing and is defined as the maximum weight that can be lifted with proper technique for only 1RM (1,2). Prescribing exercise using a percentage of a 1RM is extremely important, because certain adaptations occur (muscular endurance, hypertrophy, and strength) depending on the percentage of 1RM prescribed (5). The fitness professional may choose to estimate or actually measure an individual's strength level depending on training status (1). However, 1RM testing can be time consuming and requires considerable mental preparation by the lifter (6). By developing regression equations that allow for more accurate transition from 1 modality to another, a fitness professional will be much more effective in prescribing proper exercise and, perhaps more importantly, decreasing risk for injury to the participant because of overestimation of one's 1RM on a given modality.
An abundance of research has established equations to accurately predict a 1RM from a submaximal load being lifted in untrained women, trained women, trained men, adolescent boys, and male class athletes (3,7,8,11-13,15,17,19,22). These predictions provide valid prediction equations that save time for the fitness professional (9,14,23). They also benefit the lifter by not requiring a maximal lift and possibly reducing the risk of injury because maximal stress is not put on the musculoskeletal system (10,16).
Trial and error and a person's resistance training experience usually determine equivalent workloads for different modes. To date, there are 3 studies that provide prediction equations when switching exercise modalities (4,20,24). Cotterman et al. compared muscle force production using the Smith machine and free weights (FWs) for the bench press and the squat. The authors found differences between FW and Smith machine 1RM lifts (1RM's) for both the bench press and the squat. For all participants, the Smith machine 1RM squat was greater than the FW squat, and the FW bench 1RM was greater than the Smith machine 1RM. However, when controlling for gender, the Smith machine squat 1RM was only higher for the women, whereas for the men, there was no difference. Regression equations were appropriately developed for women only on the squat exercises and for both men and women for the bench press exercises (4). Willardson and Bressel predicted a 10RM for the FW parallel squat based on an individual's 10RM using a 45° angled leg press. Novice and trained men participated in this study, and regression equations were developed for each training status and for the entire training population as a whole (24). Simpson et al. compared 1RM's between FWs and Universal machines. Both men and women performed 1RM's on Universal Bench Press vs. FW Bench Press and on Universal Leg Press vs. FW Parallel Squat. Eight prediction equations were developed to accurately predict 1RM's from either FW to universal machines or vice versa (20). These prediction equations help fitness enthusiasts by accurately estimating a 1RM based on one's performance when using a different type of exercise equipment, by providing a more time efficient 1RM estimation, and by giving valuable information to individuals incorporating more than 1 type of exercise apparatus into their training. Practically speaking, it is extremely beneficial for an athlete to have a quantitative method of determining equivalent workloads for different modes. Although previous researchers have examined various relationships between certain modalities (4,20), there is no research examining the relationship between hammer strength (HS) equipment, which is a commonly used brand of resistance training equipment in many training facilities, to FW exercises.
The purposes of this study were to determine whether a relationship exists between 1RM performed on HS machines compared to FW and to develop regression equations that can accurately predict 1RM when switching from 1 exercise modality to another. The researchers hypothesized that the 1RM measurements from the HS machines would be greater than the 1RM measurements from the analogous FW exercises and that these differences would be statistically significant.
Experimental Approach to the Problem
The researchers approached this study with the intent to determine what descriptive variables would be significant predictors in developing a regression equation to transition from one upper-body lift to another when using HS externally loaded machines and FW. Transition between FW and HS machines (or other resistance training modalities) may be important to recreational weight lifters if they choose to add variety to their workouts, train at a different facility, or if their facility updates their equipment. It should be noted that transitioning between different modalities may lead to altered motor unit recruitment strategies, though the actual movements between modalities, for example, FW bench press vs. HS chest press, may be similar. Additionally, HS exercises may produce greater 1RMs because of less reliance on stabilizer and neutralizer muscles compared to performing the analogous FW exercises. The descriptive variables considered were height, weight, percent body fat, grip strength, and waist/hip ratio, along with 1RM.
Thirty-one trained male college students participated in this study. “Trained” status was determined as engaging in a structured resistance-training program for at least 3 months. However, the subjects' average training experience was 4.3 ± 2.7 years. None of the subjects were prior college athletes. All data were collected during the months of December and January. The Human Subjects Review Board of Western Kentucky University approved all procedures and protocols. Written informed consent and a Physical Activity Readiness-Questionnaire (PAR-Q) were obtained from all subjects. All subjects were classified as “low risk” according to the ACSM before participation (2). This study was conducted with a quasiexperimental design because of a lack of true random sampling. Validity was controlled by requiring the subjects to complete both tests within 48-72 hours and by the researcher discouraging subjects to engage in resistance training for that period.
All descriptive data were taken on the first day of testing. Subjects' height and weight were measured on a Healthometer 402KL Physician Mechanical Balance Beam Scale (Sunbeam Products, Boca Raton, FL, USA) while they were fully clothed, without wearing their shoes. The ACSM standards were used to calculate body composition using a 3-site formula (chest, abdomen, and thigh) with Lange Skinfold Caliper Model 68902 (Beta Technology, Santa Cruz, CA, USA), Country Technology, Inc. Waist-to-hip circumference was measured using a Body Tape Measure 85410 in accordance with ACSM guidelines (2). Grip strength was assessed using a Preston Grip Dynamometer (Takei Kiki Kogyo, Tokyo, Japan) as detailed by the Canadian Standardized Test of Fitness Operations Manual third Edition. Subjects were then given verbal descriptions on correct exercise techniques, and the criteria validating a successful lift were explained. A low-intensity specific warm-up (no weight) first set was observed to correct any biomechanical errors. Three testing sessions were required to complete a total of 6 1RM's, with each session requiring 48-72 hours of recovery. All sessions were counterbalanced, and subjects were maximally tested on 2 different exercise modalities in random order at each testing session. For example, a subject may have performed a 1RM on FW bench press and HS bicep curl on 1 day, followed 48-72 hours later by 1RM testing on HS chest press and FW preacher curl. No 1RM testing was done on similar body parts, or with similar movements, on the same day. All 1RM testing sessions were conducted by the same researcher to ensure consistency. 1RMs were performed only on the upper body musculature (pectoralis major, deltoids, biceps brachii). The FW exercises included the following: free weight flat barbell bench press (FWBP), free weight seated dumbbell overhead press (FWOP), and free weight bilateral preacher curl (FWPC). The HS externally plate loaded exercises included the following: iso-lateral wide chest press (HSCP), iso-lateral shoulder press (HSSP), and seated bicep curl (HSBC). These exercises were chosen because they are common upper-body movements performed by most recreational weightlifters; thus, there would likely be an interest in the transition between FW and HS equipment for these exercises. Ivanko Rubber Encased Plate w/Rubber Encased End Plate Dumbells were used for FWOP. A Pro Power PP325 Multipurpose Bench, (PRO Industries, Franklin, IN, USA) was used for FWOP. Ivanko Olympic Calibrated Competition Weightlifting Disc plates were used on a Standard 45-lb Olympic Test Bar to test FWBP. The FWBP testing took place on a PP105 Supine Bench Press. The FWPC took place on an FW 1222 Standing Preacher Curl, Body Masters Inc. (Body Masters Sports Industries, Rayne, LA, USA) Iron Grip Iron Olympic Plates were used on all HS equipment.
One Repetition Maximum Protocol
The 1RM testing was conducted according to the guidelines established in a prior research study by Earle (6). One repetition maximum was chosen as the dependent variable for this study because it is a common measure used for exercise prescription. All subjects performed a warm-up set of approximately 50% of their perceived 1RM for 10 repetitions. A 1-minute recovery was given, then a second set was performed approximately 75% 1RM for 5 repetitions. After a 2-minute recovery, a third set followed at approximately 90%, allowing 3 repetitions. After a 4-minute rest period, 1RM's were tested with increments of 5-10 lbs to maximal exertion. A 4-minute recovery was given between each maximal attempt. All rest intervals were timed using an Accusplit 601X stopwatch. The maximum weight lifted successfully and meeting all criteria was recorded as the 1RM. For all lifts, subjects used slow and controlled movements and exhaled on exertion.
A repeated-measures analysis of variance was conducted to determine whether differences existed between subjects' 1RM on HS compared to FW modalities. Regression analyses were used to generate prediction equations between modalities.
Subjects' physical characteristics are summarized in Table 1. All subjects had participated in a resistance training program for at least 3 months (4.3 ± 2.7 years). Subjects' performance characteristics are illustrated in Table 2. There were significant differences (p < 0.05) between 1RM's performed on the HS equipment compared to its counterpart FW exercise. For all exercises, 1RMs were significantly higher on HS equipment. Correlations were calculated to determine the strength of the relationship when switching from 1 exercise modality to another. Correlations were significant for all tests when predicting a 1RM for HS equipment from FW exercises.
Regression equations were developed to determine equivalent workloads for HS equipment and FW exercises (Table 3). Selected variables for each exercise were used in a forward linear regression to determine which variables explained the most variance to predict 1RM. When predicting HSSP and HSBC from their respective counterpart FW mode, the 1RM explained the greatest percentage of the variance for the 1RM on the opposite mode. Body weight and 1RM on the FWBP were significant predictors of HSCP 1RM. When predicting an FWBP 1RM from an HSCP 1RM, body fat, body weight, and HSCP 1RM were all significant predictor variables. When predicting FWOP and FWPC from their HS counterparts, there were no variables that could significantly predict their respective 1RM's. Interestingly, grip strength was not a significant predictor for any lifts.
The findings in this study are consistent with those of previous research, with individuals having a greater 1RM on machine-based equipment as compared to an FW exercise with movement specificity (4,20,24). It was hypothesized that 1RM's on the HS equipment would be significantly greater than its comparable FW 1RM. It is believed that a reduced need for balance and less muscle activity contributed toward stabilization, allowing more force to be applied in the linear path of HS machines. Although both exercises that were compared involved maximum force production of the same muscles, the movement patterns were distinctly different. An HSCP keeps the individual in an upright position, whereas an FWBP is performed while the individual is in a supine position. Also, an HSCP has a horizontal movement pattern, whereas an FWBP requires a vertical press. Because of the vertical press, the force of gravity acts against the force of the lifter, possibly causing less weight to be lifted as compared to a horizontal press where gravity would not be as disadvantageous. A limitation of this exercise was comparing a unilateral HSCP to a bilateral FWBP. Results may have been different if an FW dumbbell bench was compared because both movements would then be unilateral. However, the poundage of dumbbells was not significant enough for individuals to achieve a 1RM. The HSSP allows the individual to lean back slightly as compared to a 90° upright chair that was used for the FW dumbbell shoulder press. Both of these movements were unilateral, but because of the slight backward lean on the HSSP, it is hypothesized that the pectoralis minor may have contributed to force production, allowing more weight to be lifted. Although on the 90° upright FWOP, the majority of the stress was placed on the deltoids and because of less muscles being recruited, 1RM's were less. The HSBC and FWPC involved very similar movements, which resulted in the smallest differences in 1RM's. Because the movement patterns were so specific, as stated above, it was hypothesized that the reduced need for balance allowed HSBC 1RM's to be greater than that of FWPC.
Fitness centers offer many different types of resistance training equipment (FW, Selectorized Machines, Externally Loaded Machines). As recommended by the ACSM, a beginner resistance trainer may begin with 8-10 exercises that target the major muscle groups (chest, back, shoulders, abdomen, hips, and legs). However, as one becomes more advanced, or depending on the individual goals, other exercises will need to be performed to further elicit strength, hypertrophy, or endurance gains. This study provides regression equations for individuals looking to further advance their resistance training program by including the tested FW and HS exercises.
These equations will improve time efficiency when switching exercise modalities, especially if the Fitness Professional prescribes exercise intensity based on the percent of a 1RM. Rather than spending valuable time testing the client for a 1RM, these equations will allow the Fitness Professional to accurately predict a 1RM. These results also allow for increased safety when switching exercises. As reported by Simpson et al., there were significant differences between the Universal Leg Press and the FW Parallel Squat (20). Therefore, the regression equations from the past studies and from this study will increase the safety of the lifter when switching exercises modalities and increase the accuracy of predicting a 1RM. Future research may include similar procedures that compare free-weight movements with any type of resistance exercise equipment.
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