Introduction
During the past decade, researchers have determined that resistance training is an effective method for developing musculoskeletal strength. It is often prescribed for fitness, health, weight loss, and the prevention and rehabilitation of orthopedic injuries (1,2,3). Because strength training is an integral component in a comprehensive health program promoted by the major health and fitness organizations (e.g., the National Strength and Conditioning Association, American College of Sports Medicine, American Heart Association, and the US Surgeon General's Office), population-specific guidelines have been recently published (3,7,12).
Research on strength training has revealed improved balance and strength with both free-form training (9,13,14,23) and fixed form resistance training devices (2,12), yet research has not clearly established whether one type of training modality has any advantages over the other. Since a variety of strength training equipment is currently available, and is frequently used in various athletic and health facility settings, the purpose of this study was to compare free-form resistance training with fixed form resistance training devices to determine whether one type of training would be superior to the other relative to strength and/or balance improvements.
Methods
Experimental Approach to the Problem
In this study, previously sedentary men and women participated in a resistance training program to determine if there was a difference in strength development between fixed and free-form training devices. The author hypothesized that balance would improve more in free-form resistance training patterns and strength improvements would be similar or slightly better on fixed form devices. A 16-week training intervention was used, since this length of time was sufficient for changes to be noted from both neurological adaptation and hypertrophy.
A fixed form training device was defined as any resistance training device that had a fixed range of motion in which a user was unable to deviate from the intended range. Such an example is a leg extension machine in which the movement arm of the equipment only allows a range of motion from extension to flexion and additional movements are restricted by the equipment (Figure 1). A free-form training device was defined as any device which allowed multiple planes of motion within the intended exercise movement of the machine, although free weights would also qualify as a free-form of equipment. An example might be a chest fly machine in which movements could be changed to encompass press movements, fly movements and movements in the low horizontal, horizontal, and high horizontal planes (Figure 2).
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Figure 1: Fixed form training device.
Figure 2: Free-form training device.
Subjects
A total of thirty sedentary male and female subjects were recruited for this study (51% male and 49% female), all subjects completed the study. Inclusion criteria included being sedentary, being over thirty years of age and having no known major medical limitations to exercise. Sedentary was defined as individuals who had not been active in a regular exercise program for at least 6 months or longer (≥6 months). All subjects reported that they were free of any known significant disease, balance disorders, and cardiovascular or neuromuscular diseases. Five subjects within both exercise groups reported headaches on a frequency of 2-4 times per week prior to beginning the study. The headaches did not impede ADL's, therefore the headaches were not considered an adverse event or criteria for non-inclusion in the study. All groups were followed for a period of 16 weeks.
Procedures
All individuals attended a preliminary meeting in which they were informed of risks and benefits of participation and told not to exercise outside of the study and not to change their lifestyle, including their diet, while involved in the study. This was checked at the half way and end points of the study by questionnaire. Subjects completed an Activities of Daily Living (ADL) questionnaire, provided personal health histories including cardiovascular risk factors, documented their past and present activity history and completed a standard Participation Questionnaire (Par-Q). Before testing all subjects completed an informed consent consistent with the University of Minnesota's Institutional Review Boards policy on human subject testing. Subjects also completed a medical screening questionnaire and when necessary, obtained a release form signed by a physician.
The subjects were randomly assigned to one of three groups: Group I: Control (C n = 10), Group II, Free Form (FF group n = 10) and Group III, Fixed Form (FX group n = 10). The Control group performed no resistance training or lifestyle adjustments during the course of the study but were tested pre and post study. The FX strength group used a commercial plate loaded fixed range-motion machine (Figure 1) that provided both concentric and eccentric resistance, typically available in most health clubs. These devices included a leg press, a leg extension, a seated leg curl, a lat pull-down, a seated row, a chest fly, a chest press, an overhead press, a bicep curl, a seated tricep dip, a lower back machine, an abdominal machine, and a seated calf raise. After initial testing whereby a 10-rep maximum was obtained, subjects were asked to perform one set of 8-12 repetitions to muscle failure. Muscle failure was defined as not being able to perform another repetition with perfect form. Once 12 repetitions were obtained with good form, a standard 5% increase in resistance was assessed and the subject again performed one set until they again reached 12 repetitions. The FF resistance training group also used a commercially available training machine (Figure 2), typically found in many health clubs; these training devices included the squat machine, the quadriceps extension, a hamstring curl, a calf raise, a lat pull down, a row machine, a chest press, a shoulder press, a bicep curl, a tricep extension and a standing abdominal machine. Because the manufacturer of the free-form equipment did not offer a low back exercise, the biceps machine was modified in a way that the subject could perform a split-stride lumbar extension by maintaining a fixed pelvic position and executing a lumber extension. The FF group were also assessed a 10-rep maximum pretest value, then performed one set of 8-12 repetitions to muscle failure and then the resistance was increased by 5% once 12 repetitions with good form had been obtained. Both groups performed a warm-up set of 50% of their 10 RM weight. The FF group was also further challenged by changes in stability. This occurred in 3-week segments during the study in which the participants were asked to move from a sitting to a standing position, with and without support, and perform various movement patterns which involved rotating, twisting and lifting on a proprioceptively enriched surface. Free-form equipment was defined as equipment that allowed the user multiplaner motion without fixed angles. This equipment was plate loaded and cable assisted. Since it was cable based and the equipment allowed motion in multiple ranges within the exercised joints capability, it was considered free-form as defined by the fitness industry.
Subjects in the FF and FX groups performed one set of 8-12 repetitions to muscle failure two times per week. One additional set was used as a warm-up prior to testing. To begin, starting weight was determined over three exercise sessions and starting resistance was based on a resistance that the subject could lift ten times without form break [10 repetition maximum (10 RM)]. This resistance was then used as the baseline. When the subject was able to perform 12 repetitions without breaking form, the equipment resistance was increased by a standard 5% in accordance with National Strength Conditioning Guidelines (10). The general guideline for repetitions was 8-12 per set, performed with proper technique to the point of muscle fatigue. Studies show that 8-12 repetitions can typically be completed with weight loads between 70 to 80% of maximum resistance (8,21). Each subject performed a single warm up set and one set of 8-12 repetitions to muscle failure on each work-out machine.
Verbal responses were collected at each exercise session and included: frequency of headaches, pain scales (using a scale of 0-10 whereby 0 = no pain and 10 = severe pain), sleep quality, energy levels, and stress. Additional baseline data collected included.
A BOSU Balance Test
Subjects were asked to stand on one leg on the flat surface of a floor (5,16,17). Younger subjects were able to balance on the flat floor surface for longer periods at base line when compared to older subjects. There was a concern that different levels of muscular fatigue could affect the test results rather than the ability to balance. There may also have been a ceiling effect. Therefore, subjects were asked to stand on one leg on the dome surface of a BOSU ball. This ball was positioned with the flat surface down and dome surface up. All subjects were able to balance on the dome surface with appropriate support if needed. Once balance was obtained, the subjects were asked to stand on one leg and balance without arm support. A stop watch was used to measure the length of time that the subjects could maintain their balance. Timing began when the subjects obtained a one-legged balance position without arm support. The measurement ended when the non-supported leg touched down or the subjects touched the safety bar. Each leg was timed for the best of three attempts, and the highest score was recorded.
A Sit and Reach Test
For this test, the subjects sat on the floor with legs forward and feet up. The subjects' feet (shoes off) were placed 10.16 centimeters (4 inches) apart and flat against a box. The subjects were instructed to keep the back of both knees flat against the floor, then they were asked to slowly exhale and lean forward with the hands overlapped without bouncing or jerking. The score was recorded using a measurement stick placed between the heels with the 31.1 centimeters (15-inch) point at the heel base. The distance was recorded in centimeters reached measured by the tips of the fingers. The test was repeated twice and the best score was recorded. This test followed the procedure described by Pepin, Phillips and Swan (16).
Statistical Analyses
The subjects were statistically assessed pre- and posttest between groups. Because the subjects were randomly assigned, a one-way analysis of variance (ANOVA) was used to compare pre- and posttest measures. The level of significance for all tests was accepted at P ≤ 0.05. Verbal feedback was also obtained for headache frequency and pain scales on a 0-10 scale were used to assess any discomfort experienced during the period of analyses.
Since the exercise subjects were measured on equipment that they used in training, and since that equipment was different (fixed versus free-form) the outcome results of each group were subject to the influence of different movement patterns and exercise equipment. However, with each group training the same muscle groups, the percent improvement in each group could be compared from start to end. For this reason a one-way analysis of variance (ANOVA) was used to evaluate the groups by percent of improvement of each study participant. Statistical significance was accepted if P ≤ 0.05. Because the total number of subjects was low, no additional statistical data were collected other than those looking at a total percent of improvement.
Results
The total starting resistance weight (in kilograms) was compared to the end resistance weight (in kilograms), based on a 10-RM test. A 1-RM strength test was not performed since the study's aim was to compare free-form strength with fixed-form strength; thus no single test could have been used without risking a biased outcome. Further, research indicates a reasonable correlation between 1RM and 7-120RM measurements (24). The results of the testing revealed that strength measured by starting and ending total resistance improved in both groups (Table 1). However, the free-form group elicited a strength improvement of 115% compared to the fixed group 57%, When compared this yielded a statistically significant improvement (P = .000001, Table 2). These data indicate that free-form training is a more effective means of improving a user's overall strength. When the FF group was compared with the control, outcomes were equally as compelling (Table 3).
Table 1: Summary of Strength Improvement
Table 2: ANOVA Summary Statistics between FX and FF groups
Table 3: FF group compared to control
Balance, which has been shown to have a strong negative correlation with frequency of falls, especially in the elderly (4,5,11,13), improved in this study in both groups (Table 4). More specifically, in the standing balance test, the FX group improved 49%, supporting past research that strength training can improve balance and reduce the risk of falls (17,18,23).
Table 4: Summary Balance Improvement (in seconds)
Interesting to note are pain level scores for the two exercising groups (Table 5). The frequency of headaches in both groups dropped significantly (50%). Frequency of headaches was reported verbally based on the number of headache episodes experienced prior to training and since the last training session. Headache frequency was considered from a questionnaire at the beginning of the study (pre-training) and compared with the frequency at the end of the study (post-training). The mechanism for headache reduction was not clear during the study; however, based on participant feedback the reduction may be associated with stress and tension reduction as a result of exercise. Overall joint pain (measured on a 0-10 scale) in the FX subjects, increased 111%, while the pain scores of the FF subjects, some of whom had known pre-existing but not debilitating pain, experienced a 30% reduction in overall pain with no new symptoms of pain from the training. This was particularly interesting since the FX had no prior joint concerns or reported pains before training began.
Table 5: Summary Self Reported Pain (0-120 scale)
Discussion
The purpose of this study was to compare measures of balance and strength between subjects who use fixed training equipment and free-form training equipment. Measures of standing balance and strength were compared in subjects who participated in a fixed resistance training program and a free-form resistance training program. While it is accurate to argue that the forms of resistance were not identical, the results clearly demonstrated that both trained groups benefited from improved strength and balance; however, the free-form group improved more than the fixed form group as an overall percentage of gain.
Initially, it was hypothesized that FX subjects would improve significantly more than FF subjects in overall strength. This hypothesis was primarily due to FX subjects performing a standard 12 repetition program in which a uniform 5% increase in resistance was applied once 12 repetitions had been achieved. The increases in resistance were therefore uniform and anticipated. In the FF subjects however, while the same basic one set of 12 repetition principle was applied, the subjects were challenged every 3 weeks by changes in stability. For instance, while the FX did not change position (fixed), the FF group went from sitting supported to sitting without support, to standing to various movement patterns involving rotating and twisting and while balanced on a wobble board or a proprioceptively challenging surface. This change in challenge followed basic recommendation guidelines from the manufacturer and industry leaders. Upon each change in challenge, the FF group was required to significantly reduce resistance until they acclimated to the new movement pattern and resistance. Thus, it was assumed that the FX, who was fixed in progression as well as position, would improve over the FF subjects. Yet, the FF group actually improved their strength 58% greater than the FX group.
Balance increased in the free-form group more than twice the value of the fixed group (49% versus 245%). The balance improvement was not necessarily surprising since the free-form group was required to exercise both in stable and unstable positions and the fixed group was not. Of interest however, is the obvious advantage of incorporating balance activities into strength training rather than requiring individuals to strength train on equipment that does not enhance balance. This may be especially true in high fall risk populations. The use of balance devices in a training program is appropriate since proprioceptive rehabilitation programs often prescribe balance training devices, such as unstable balance platforms, in order to address balance and proprioceptive deficits and restore functional stability of the ankle joint (15). Balance training has also shown improved performance with selected sport-related activities (14,22). Other tests, such as the Tinetti Balance Assessment and a Berg Balance Test (4,19,20), were used but were found to be age-inappropriate and thus not reliable tests. Younger subjects easily scored high points on these tests and thus would have created a ceiling effect. The control group, who did not exercise showed no improvement in strength or balance in the 16-week period.
These data appear to support the position of free-form training advocates who suggest that the mechanical systems of the body are complex, multiarticular systems that require muscular synergy and balance (6,9,14,22). Results in both strength and balance indicate that fixed training patterns, while they isolate and strengthen, may not promote natural movement patterns and, due to their fixed pattern of movement could hypothetically promote injury or pain in both athletic and exercising populations due to their inability to strengthen a system as a functional unit and due to their fixed pattern of overload. This theory, while hypothetical, may find support based on strength and balance improvements and by observations of increased pain in the FX subjects and decreased pain in the FF subjects.
Practical Applications
This study finds that the assumptions in fixed training (i.e., it is better to isolate a muscle in order to strengthen it), may be inaccurate. There appears to be a relationship with free-form movement patterns that is dependent on all muscles within that movement pattern (closed kinetic chain) being trained as a single unit rather than isolated into specific muscles. An overhead press motion for instance does not only involve the shoulder joint, but also the coordinated and synergistic contribution of muscles and joints controlling the scapula, clavicle, and ribs in order to accomplish that movement. An injury is assumed to occur to whatever muscle is weakest in any closed kinetic chain. This muscular weakness may, in fact, be augmented by isolation training and corrected through free-form training. In short, movement is not the result of isolated actions of individually working muscles but the complex interrelationship of many muscles and joints stabilizing and contracting concurrently and sequentially. This “synergy” is further complicated by the difference between “machine” movements and “life” movements. Movements in life are neither fixed nor isolated. In pathological and non-pathological movement, the nervous system will select a motor strategy that is optimal for the movement pattern being performed. This requires strength in all ranges and motions, not any one fixed and isolated movement. The selection of the optimal movement pattern is also dependent on the freedom to migrate a movement pattern into a pattern less stressful for the participant. Results of this study therefore seem to indicate that free-form training might prove more beneficial in developing strength and balance, especially for the elderly and further research should be conducted in this regard.
In addition to the findings of this study, the subjects, who participated at a rate of 98% compliance, were asked why they remained in the study and why they did not quit. The two most prevalent reasons for compliance were 1) obligation to the study and 2) not wanting to let down the trainer. When asked if they would have considered quitting if the frequency of exercise had been three times per week versus only twice, 50% said they would have quit. This response may have important implications when considering the initial training frequency of new clients.
Data also from this study indicate that another hypothesis for repetitive stress injuries (RSI's) may be that injuries are more associated with imbalance in muscle synergy sequencing than simply a case of overuse and micro-trauma. This hypothesis is based on the studies results, and observations in athletic populations who are consistently involved in repetitive motion but appear also to develop balance in muscular strength. It is feasible that over developing one muscle group, such as the repetitive movement pattern required of a job function (i.e., stacking boxes), renders an imbalance that may alter muscle sequencing and posture, leading to more stress and ultimately pain or injury. While only a hypothesis postulated by this author, data warrants that more research in this area may be beneficial.
There are several aspects of the study that should be considered when analyzing the results. Since the average age range was 49 (±3.7 years), age related factors may have influenced the results of this study. Likewise, older individuals may experience a slower learning curve than younger subjects, or some subjects may have been balance challenged before the study which dramatically affected results through improvement during the study. All subjects who participated in the program had reported various sinus, allergy or cold infections which could also have affected the outcome of the testing given the low subject pool. Since a single set was used over higher volume protocols it is accepted that higher volumes of training may have produced different results. This hypothesis should be explored in future studies.
In summary, the key findings of this study revealed improved balance and strength in the test groups, but improvements appeared significantly greater in the free-form trained groups over the fixed or linear trained groups. Limitations of this study included: the age range was limited and the subject pool was relatively small. However, the changes in strength and balance were statistically significant regardless of the above mentioned factors. Further research is warranted, perhaps with a larger subject pool to confirm these initial findings. Additionally, more research should be conducted using higher intensities and greater volume to determine whether these mechanisms affect the outcomes. Without question this training format had advantages for beginner exercisers. It is assumed that these same advantages would be available to advanced lifters if adjusted for volume and intensity.
Acknowledgments
The author would like to gratefully acknowledge Arlene Eliason for her assistance in proofing, feedback, and statistical analysis. Thanks are extended to the FreeMotion Corporation for risking their theories on scientific study and for their generous donation of exercise equipment.
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