The Effects of Ten Weeks of Lower-Body Unstable Surface Training on Markers of Athletic Performance
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Journal of Strength and Conditioning Research, 2007, 21(2), 561–567 ᭧ 2007 National Strength & Conditioning Association THE EFFECTS OF TEN WEEKS OF LOWER-BODY UNSTABLE SURFACE TRAINING ON MARKERS OF ATHLETIC PERFORMANCE ERIC M. CRESSEY,CHRIS A. WEST,DAVID P. TIBERIO,WILLIAM J. KRAEMER, AND CARL M. MARESH Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, Connecticut 06269. ABSTRACT. Cressey, E.M., C.A. West, D.P. Tiberio, W.J. Krae- such training will enhance performance via improvement mer, and C.M. Maresh. The effects of ten weeks of lower-body of balance, kinesthetic sense, proprioception, and grada- unstable surface training on markers of athletic performance. J. tion of force (8, 27). These supporters claim that because Strength Cond. Res. 21(2):561–567. 2007.—Initially reserved for all movement requires both stability and mobility, it is rehabilitation programs, unstable surface training (UST) has re- cently grown in popularity in strength and conditioning and gen- valuable to train the 2 qualities simultaneously (8, 27). eral exercise scenarios. Nonetheless, no studies to date have ex- Both efferent and afferent processes modulate neuromus- amined the effects of UST on performance in healthy, trained cular function, yet little research has focused on the ef- individuals. The purpose of this study was to determine the ef- ferent component. Unstable surface training aims to de- fects of 10 weeks of lower-body UST on performance in elite ath- velop afferent efficiency to reduce injury risk and improve letes. Nineteen healthy, trained members (ages 18–23 years) of performance (8, 14, 27); such training may help to estab- a National Collegiate Athletic Association Division I collegiate lish proper agonist-antagonist cocontraction for joint sta- men’s soccer team participated. The experimental (US) group (n ϭ bility and improve rate of force development (14). Effi- 10) supplemented their normal conditioning program with cient afferent function is crucial to neuromuscular exci- lower-body exercises on inflatable rubber discs; the control (ST) group (n ϭ 9) performed the same exercises on stable surfaces. tation; potential improvements in this regard include Bounce drop jump (BDJ) and countermovement jump (CMJ) more rapid proprioceptive input collection, information heights, 40- and 10-yard sprint times, and T-test (agility) times transmission to the central nervous system, and infor- were assessed before and after the intervention. The ST group mation processing by the central nervous system (15). improved significantly on predicted power output on both the Afferent efficiency is valuable in injury prevention, be- BDJ (3.2%) and CMJ (2.4%); no significant changes were noted cause short latency periods before muscle activity allow in the US group. Both groups improved significantly on the 40- for rapid stiffening of joint complexes (14). In limited re- ϭϪ ϭϪ ϭ (US 1.8%, ST 3.9%) and 10-yard sprint times (US search, wobble board training has improved discrimina- Ϫ4.0%, ST ϭϪ7.6%). The ST group improved significantly more than the US group in 40-yard sprint time; a trend toward great- tion of ankle inversion movements in already-stable an- er improvement in the ST group was apparent on the 10-yard kles of athletes and the elderly (36); however, control sprint time. Both groups improved significantly (US ϭ 2.9%, ST groups did not exercise in these studies. Similar results ϭϪ4.4%) on T-test performance; no statistically significant were noted in youth soccer players (35), but previous in- changes were apparent between the groups. These results indi- jury history was not considered; some subjects may have cate that UST using inflatable rubber discs attenuates perfor- simply been correcting existing injury-related propriocep- mance improvements in healthy, trained athletes. Such imple- tive deficits. Regarding performance, UST improved rate ments have proved valuable in rehabilitation, but caution should of force development without a concurrent increase in be exercised when applying UST to athletic performance and general exercise scenarios. maximal static leg press strength in untrained subjects (14), although no control groups were used to allow for KEY WORDS. instability, stability, balance, power, propriocep- comparison to stable surface exercise. Conversely, Bruhn tion, stretch-shortening cycle and others (9) found a stable surface program to be su- perior to UST with respect to postural stabilization, max- INTRODUCTION imal voluntary isometric contraction, and countermove- nstable surface training (UST) has recently ment jump (CMJ) height. grown in popularity in strength and condition- There remains considerable opposition to using UST ing and general exercise scenarios. Although outside of rehabilitation settings in spite of its purported UST has proved valuable in rehabilitation set- benefits; opponents speculate that UST may undermine U tings, especially with respect to addressing training specificity, lead to unfavorable biomechanical proprioceptive deficits related to functional ankle insta- compensations, and impair the development of athletic bility (25, 39), little research has examined how UST af- qualities. Unstable surface training has been shown to fects healthy, trained athletes. Nonetheless, many com- increase core musculature activation when compared panies and strength and conditioning professionals have with stable surface exercises (6, 22), but these studies capitalized on this trend by promoting UST products as have been performed with the torso on the unstable sur- useful for improving performance. face (i.e., exercises targeting the trunk) rather than the Unstable training implements, including stability lower extremity; such results may not be applicable to the balls, wobble boards, foam pads, and balance discs, reduce present study. Increasing core stabilizer activation with (or eliminate) an individual’s points of contact with solid lower-body UST may not favorably influence dynamic ground. Unstable surface training proponents assert that movements; standing UST exercises do not stress the core 561 562 CRESSEY,WEST,TIBERIO ET AL. in a similar manner to trunk-specific exercises (e.g., curl- did not undergo a lower-body UST intervention and those ups), in which the overall stability challenge is less dif- who did. ficult. Swiss ball training improved core stability in young athletes but did not favorably affect abdominal and erec- METHODS tor spinae electromyographic activity, VO2max, running Experimental Approach to the Problem economy, or running posture (31). Likewise, no correla- tion existed between wobble board performance and hock- A pretest, posttest control group design was utilized for ey skating speed in players older than age 19 years (7). this study. Subjects were matched for age and position These findings support previous evidence (13) that there (goalkeeper, defender, midfielder, and forward to account is little carryover from static to dynamic balance. Balance for varying activity levels during training and competi- tion) and then randomly assigned into either the experi- and stability are skill specific; UST, which necessitates ϭ ϭ predominantly static balance, may not transfer to most mental (US, n 10) or control (ST, n 9) group. athletics, which require more dynamic balance (10). Fi- Subjects nally, incorporating UST to a neuromuscular recruitment pattern for a given activity (e.g., throwing on an unstable Nineteen members of a National Collegiate Athletic As- surface) may negatively affect chronic performance of sociation Division I collegiate men’s soccer team (ages 18– that skill (39). 23 years) with considerable resistance training experi- Core musculature activation is significantly greater ence were chosen to participate in this study. All subjects under unstable squat conditions than stable conditions had a minimum of 6 months of resistance training expe- (2), and instability with trunk-strengthening exercises in- rience but no involvement in UST or ankle sprain history creased activation of the lower abdominal muscles (6). over the previous 6 months. Each subject provided writ- However, force production under stable conditions is ten informed consent prior to entry in the study, which markedly greater than under unstable conditions, and was approved by the institutional review board of the antagonist activity is significantly higher with instability University of Connecticut. (5). Behm and colleagues (5) attributed this altered re- Pretesting cruitment to ‘‘excess stress associated with the increased postural demands’’ (muscles stabilizing joints rather than All subjects took part in pretesting during their normally promoting movement) and ‘‘the dispersion of concentra- scheduled January testing week. The testing was carried tion [neural drive] in attempting to control 2 limbs with out in 1 day in the following order: bounce drop jump differing responsibilities [balance and force].’’ Overall (BDJ), CMJ, 40-yard sprint test (with assessment of a 10- electromyographic activity is unchanged because limb yard sprint time), and T-test. The testing session took ap- musculature is called upon to aid in maintaining joint proximately 1 hour, and subjects were given ample time stability with instability (3, 6, 20). to recover between each test. All subjects were proficient Although stable surface free weight exercises have with each of the tests, so no familiarization session was been proved safe (41), no studies have examined injury necessary. Prior to testing,