Does Mini-Trampoline Training Reduce Lower Limb Asymmetries?

INTRODUCTION: Inter-limb asymmetry is defined as the performance imbalance (i.e. strength, balance) of a limb with respect to the other. Asymmetries between limbs are influenced by several factors as lateral dominance (left vs right), injuries and sports. In particular, team-sports athletes exhibit significantly greater inter-limb asymmetries with respect to non-athletes, due to the large number of unilateral actions such as jumping and changes of direction. Studies widely demonstrated how plyometric and balance trainings could minimize inter-limb imbalance by reducing asymmetries and the relative risk of sport-related injuries. Among the different plyometric training modalities, an effective method is repre-sented by mini-trampoline training, such as SuperJump (SJ). Therefore, this study aimed to evaluate the acute effects of SJ on dynamic balance Unilateral Asymmetry Index (UA). METHODS: 37 healthy subjects were randomly allocated in SJ group (SJG n=20) and Control group (CON n=17). SJG partici-pated in SJ session, whereas CON did not receive any workout. SJ included a 30-min workout with a warm-up including mobility exercises, a central phase with jumping exercises alternating movements of upper and lower limbs and a cool-down. Before (PRE) and after (POST) SJ subjects performed Wobble Board (WB) balance test consisting of 3-min of free familiarization with the board followed by 1 test trial of 30s per limb with 1-min of rest in between. Subjects stood barefoot on the board in a single leg stance by adopting a comfortable and central foot position, knee slightly bended and hands on the hips. To visualize real time balance performances on a monitor, subjects were asked to focus on a motion marker (MM) and try to minimize its displacement with the aim of keeping it inside the target zone (TZ) as long as they could. WB performance was represented by the time the MM spent in the TZ. To evaluate the magnitude of UA Index, the formula [(100/high·low)·-1]+100 was used, where high and low correspond to the greater and lower limb values for WB test. RESULTS: The linear repeated measures mixed model analysis showed significant differences (F(3,35) = 3.29; p=0.005) for UA Index between PRE (36.9±27.7%) and POST (17.9±13.6%) in the SJG. No differences were found PRE (32.2±19.3%) and POST (30.5±15.0) for the CON group. CONCLUSION: Results suggested that SJ training played a key role in reducing UA. Structured training programs aiming at eliminating or limiting the asymmetries, should not only focus on the execution of exercises for the less performing limb. In fact, monopodalic training could lead to a change in the direction of asymmetry, from the dominant limb to the non-dominant one or conversely, by not getting improvements in UA. Therefore, bipodalic exercises, such as repetitive vertical jumps on SJ, could represent an important method in improving UA in healthy young and athlete population.