Acute joint range effects of exercises at different strength intensities on unstable and stable platforms.
While traditional strength exercises are commonly performed on stable surfaces, the use of unstable surfaces is becoming an important strategy for the implementation of power exercises. The latter's popularity is associated with a greater use and application of the neuromotor and neuromuscular systems (8). In fact, it would be difficult to find a fitness facility without an instability device such the Swiss ball. It is an unstable base, which is considered to be an important piece of equipment that is believed to improve physical fitness (13) and promote motor control adaptations.
Interestingly, the resistance training literature does not speak to either positive or negative effects on joint range of motion exercises performed on unstable platforms. However, assuming that the inherent instability of a stable training platform requires major adaptations of the neuromuscular system (5) and that range of motion is related to the improvement of neural activities (9), it seems likely that modifying the proprioceptive system with an instability device should produce a positive influence on the range of motion of specific joints.
Studies (7, 11) have shown the influence of traditional strength training intensity on range of motion (i.e., flexibility). Fatouros and colleagues (7) analyzed the effects of 24 wks of strength training at different intensities (low intensity = 45 to 50% of 1RM, moderate intensity = 60 to 65% of 1RM, and high intensity = 80 to 85% of 1RM) on flexibility. They concluded that flexibility demonstrated an intensity-dependent enhancement (3 to 12% in LI, 6 to 22% in MI, and 8 to 28% in HI). Clearly, the findings indicate that resistance training has a positive influence on range of motion.
Similarly, Novaes Neto et al. (11) compared the acute effects of training at different intensities of resistance exercise (40%, 60%, 80%, and 100% of 1RM) on range of motion and found major changes at the intensity of 80% 1RM. Relative to an unstable platform, it is possible that different intensities promote greater adaptations in joint range due to increased proprioceptive system use, which may alter the length-tension relationship of the neuromuscular system.
Given that there is limited information regarding changes in flexibility with resistance training carried out on unstable platforms, the purpose of the present study was to compare the acute effect of a strength exercise at different intensities of 60% and 80% of 1RM while using a stable platform (flat bench) and an unstable platforms (Swiss ball) on joint range in recreationally trained men.
Twenty-six recreationally trained male volunteers (23.2 [+ or -] 3.7 yrs of age, 79.6 [+ or -] 12.3 kg, 1.77 [+ or -] 0.07 m, 25.4 [+ or -] 2.9 kg/[m.sup.2]) participated in the study. Based on an a priori analysis, the sample size was determined to be sufficient to provide statistical power of 85.1%. Following the recommendations of Beck (4), a power of 0.85, [alpha] = 0.05, correlation coefficient of 0.5, nonsphericity correction of 1 and an effect size of 0.25 resulted in an N of 26 subjects. This a priori analysis of the statistical power was performed to reduce the probability of type II error and to determine the minimum number of participants required for this investigation. It was found that the sample size was sufficient to provide statistical power of 85.1%.
Subjects' participation was allowed if they: (a) were not smokers; (b) did not have some type of musculoskeletal injury; and (c) did not respond positively to any of the items of the Physical Activity Readiness Questionnaire / PAR-Q (8).
The study was carried out over nine visits on non-consecutive days. On the first visit, after being informed of the risks and benefits, the subjects read and signed an informed consent form and underwent an anthropometric assessment that was followed by a range of motion test. On the second visit, the range of motion was retested. On the third visit through the fifth visit, the subjects performed a familiarization bench press exercise on an unstable platform. From the sixth visit, the subjects were randomly assigned to input offset in the following experimental conditions: (a) 60% of 1Rm on the stable platform; (b) 80% of 1RM on the stable platform; (c) 60% of 1RM on the unstable platform; and (d) 80% of 1RM on the unstable platform.
Test of 1MR
Maximum dynamic strength was evaluated using the American College of Sports Medicine's (1) recommendations for performing dumbbell press exercises on a flat bench. The subjects performed the 1RM test. Then, they were retested after 48 hrs to verify the reproducibility of the loads encountered.
Standardized instructions regarding the procedures were previously provided. Also, various strategies were adopted to minimize errors during the 1RM test. The subjects were verbally encouraged and performed four trials for each exercise with a standardized rest interval of 5 min between attempts. The maximum load achieved in the last full run was recorded as 1RM.
Range of motion was assessed in four joint movements of the shoulder: (a) flexion; (b) extension; (c) abduction, and (d) horizontal adduction. All flexibility measurements were made on the right side of the subjects, which was followed by a retest to verify the reproducibility of the results. Flexion, extension, and abduction were performed with greater ease due to lying to neutralize the possible compensatory movement of the subjects. Horizontal adduction of the shoulder was verified with each subject sitting in a chair. To assess range of motion, the appraiser adjusted the subject's body to the point of pain or anatomical limitation. The measurements were made using a Carci (0.20 x 0.05) goniometry, using the procedures described by Norkin and White (10). The data collected at the beginning were not available to the evaluator during the subsequent evaluation.
The parametric assumptions of normality and sphericity were validated using the Kolmogorov-Smirnov test and Mauchley test, respectively. The results are presented as the mean [+ or -] standard deviation (M [+ or -] SD). A two-way ANOVA for repeated measures was used to test the effect of the intensity and the type of platform on joint range. When the interaction between factors was significant, paired t tests with Bonferroni correction were used to detect specific differences. Paired t tests were performed to compare the differences in range of motion after exercise sessions with pretest values. The reproducibility of the measurements was assessed using an intraclass correlation coefficient (ICC). All statistical analyses were made using SPSS software (v.19, SPSS Inc., Chicago, IL, USA), with a significance level of 5% (P [less than or equal to] 0.05).
An intraclass correlation coefficient was used to verify the reproducibility of the mean values in the range of motion tests. High correlation coefficients were observed (r = 0.99) with no significant differences between the test and retest range of motion.
Table 1 shows the effects of intensity and the type of platform on shoulder range of motion. Flexion, extension, abduction, and adduction are shown horizontally. Shoulder flexion range of motion was significantly greater after exercises performed at the intensity of 80% of 1RM versus the intensity of 60% of 1 RM (P<0.001).
With respect to shoulder abduction, range of motion was greater after exercises at 80% of 1 RM rather than after exercises at 60% of 1RM (P=0.001), and on an UP rather than on a SP (P=0.03). However, shoulder adduction was observed at a higher amplitude after exercise was conducted on an UP versus on a SP (P=0.005).
When comparing the joint range of motion for the pre-test and post-test values, greater shoulder flexion (156.0 [+ or -] 12.2 vs. 150.5 [+ or -] 15.0; P = 0.01) and shoulder abduction (157.1 [+ or -] 16.2 vs. 149.1 [+ or -] 19.6; P = 0.02) were observed after sessions held on an UP at 80% of 1RM versus the pre-test. With respect to shoulder adduction, higher values of joint amplitude were observed after the sessions using an UP at 60% of 1RM (44.9 [+ or -] 10.2; P = 0.02) and 80% of 1RM (45.4 [+ or -] 12.9; P = 0.02) versus the pre-test (38.0 [+ or -] 13.7).
The purpose of the present study was to compare the acute range of motion effects of bench press exercises on an unstable platform (UP) and a stable platform (SP) at the intensities of 60% and 80% of 1RM. Our main finding was that resistance exercise performed on an UP increased horizontal abduction and adduction shoulder flexibility compared to exercise performed on a SP. These findings are especially interested since there appears to no studies in the scientific literature that reported on the range of motion effects of resistance exercise performed on an UP.
It is believed that the results found in the present study are a function of the changes in the proprioceptive system caused by the instability during exercise (2). The proprioceptive system is composed of muscles, tendons, and joints as well as proprioceptors by nociceptors, which are essential mechanisms for the protection and organization of the complex structures involved in human movement (3). Thus, it is speculated that a possible change in the sensitivity of proprioceptors and the nociceptors may have modified the neurophysiological aspects of movement control, as well as the pain threshold. The result is an increase in the subjects' range of motion when performing exercises on the UP. Thus, it is suggested that instability produces a positive response in flexibility.
Relative to intensity, the results of this research showed that exercise performed at 80% of 1RM compared to 60% of 1RM increased joint motion in abduction and flexion amplitude on both platforms amplitude. It is possible that the increased intensity caused increased tension and consequent muscle-tendon autogenic inhibition due to the action of the Golgi tendon organs (6). In this sense, the use of the higher intensity during resistance exercise seems to produce a reflex inhibitory response of greater magnitude that results in lower passive tension that generates an increase in range of motion.
Results consistent with the present study were found by Fatouros et al. (7) and Novaes Neto et al. (11) in traditional training. Fatouros et al. (7) examined the influence of different intensities of force (40%, 60%, and 80% of 1RM) on flexibility after 6 months of training and detraining. The authors concluded that percentages above 60% of 1 RM are effective for generating flexibility gains in elderly individuals. Although Fatouros et al. (7) observed the chronic effect of traditional strength training intensity on flexibility in the untrained elderly and the present study verified the acute effects in young trained subjects, it is very likely there is a direct relationship between the findings of both studies.
Recently, Novaes Neto et al. (11) compared the effect of different intensities on joint range in young trained participants. Their subjects performed the bench press and leg press exercises at intensities of 40%, 60%, 80%, and 100% of 1RM. The authors found significant differences in the range of motion in flexion, abduction, and horizontal adduction for the protocol at 80% of 1RM compared with those at pre-test. For the same training intensity compared to the pretest, the present study found differences in the same joint movements in the bench press exercises performed on the UP, which confirms the findings of Novaes Neto et al. (11) in traditional training. This increase from the pre-test values indicates that, regardless of the platform, the exercise of force alone is able to improve range of motion.
Given that much of the population has the objective of achieving maximum physical fitness results in minimum time, the UP provides more efficient training. Also, the exercise performed at high intensity maximizes the effects on neuromuscular and neuromotor fitness.
Our study supports the hypothesis that bench press exercises at an intensity of 80% of 1RM on an unstable platform promotes improved range of motion in shoulder flexion, abduction, and horizontal adduction in trained men.
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Amanda Brown , Jeferson Vianna , Ingrid Dias , Humberto Miranda , Gabriel Rodrigues Neto , Jefferson Novaes 
 Physical Education Graduate Program, Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, RJ, Brazil,  Physical Education Post Graduation Program, University Federal of Juiz de Fora, Juiz de Fora, Brazil,  Medical Clinic Post Graduation Program, University Federal of Rio de Janeiro, Rio de Janeiro, Brazil
Address for correspondence: Amanda Fernandes Brown, MSc, Rio de Janeiro Federal University, Physical Education Graduation Program. Rio de Janeiro - RJ, Brazil. Zip-code 21941-590. Phone +55 32 9181 9213, Email: firstname.lastname@example.org
Table 1. Mean [+ or -] Standard Deviation of Shoulder Range of Motion after Bench Press Pre-Test and at 60 and 80% of 1RM Performed on a Stable and Unstable Platform. Pre-Test 60% SP Flexion 150.5 [+ or -] 15.0 144.4 [+ or -] 19.8 (degrees) Extension 17.1 [+ or -] 3.9 17.5 [+ or -] 3.8 (degrees) Abduction 149.1 [+ or -] 19.6 145.2 [+ or -] 17.5 (degrees) Horizontal 38.0 [+ or -] 13.7 37.6 [+ or -] 11.2 Adduction (degrees) 60% UP 80% SP Flexion 148.2 [+ or -] 16.1 153.0 [+ or -] 15.5 * (degrees) Extension 17.8 [+ or -] 3.9 17.2 [+ or -] 3.2 (degrees) Abduction 149.1 [+ or -] 153.6 [+ or -] 14.9 * (degrees) 18.0 ([not equal to]) Horizontal 44.9 [+ or -] 41.8 [+ or -] 13.0 Adduction 10.2 ([not equal to][dagger]) (degrees) 80% UP Flexion 156.3 [+ or -] 12.2 *([double dagger]) (degrees) Extension 17.8 [+ or -] 3.7 (degrees) Abduction 157.1 [+ or -] 16.2 *([not equal to][double dagger]) (degrees) Horizontal 45.4 [+ or -] 12.9 ([not equal to] [double dagger]) Adduction (degrees) SP = stable platform; UP = unstable platform. * significant difference between the intensities (60% vs. 80%). ([not equal to]) significant difference between the platforms (UP vs. SP). ([double dagger]) significant difference pre-test vs. 80% UP. ([dagger]) significant difference pre-test vs. 60% UP. (P<0.05)
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|Author:||Brown, Amanda; Vianna, Jeferson; Dias, Ingrid; Miranda, Humberto; Neto, Gabriel Rodrigues; Novaes, J|
|Publication:||Journal of Exercise Physiology Online|
|Date:||Dec 1, 2014|
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