Contact Time Predicts Coupling Time in Slow Stretch-Shortening Cycle Jumps

PURPOSE: This study was designed to examine the relationship between contact time and coupling time in slow stretch-shortening cycle (SSC) jump conditions. Coupling time has been defined as the transition time between the eccentric and concentric phases of the SSC. Short coupling times are thought to be related to a more efficient utilization of elastic energy in the SSC. Similarly, short contact times (i.e., duration of the SSC) are also important for maximizing the potentiating effects of the SSC. While it has been suggested that coupling time and contact time are linearly related, the exact relationship has not been adequately defined. METHODS: Eight plyometrically trained male varsity athletes performed a series of six slow SSC jumps. Lower limb kinetic and kinematic data were collected by way of a force plate and a six-camera motion analysis system sampling at 800 Hz and 200 Hz, respectively. The slow SSC jump was operationally defined as a drop jump involving a rebounding vertical jump for maximum height, with a contact time greater than 0.25 seconds. Contact time was calculated as the period in which ground reaction forces were recorded in force plate data during the vertical jump rebound. Knee angular acceleration curves were analyzed for all jumps, with coupling time calculated as the time between the peak eccentric and concentric phase angular accelerations. RESULTS: Contact times and coupling times ranged from 0.27 - 0.62 and 0.05 - 0.39 seconds, respectively. Coupling time was found to be significantly positively correlated to contact time (p < 0.01). CONCLUSIONS: The results demonstrated that 81.3% of the variance in coupling time can be accounted for by contact time, and as such coupling time can be accurately predicted from contact time in slow SSC jump conditions. Slow SSC jumps displayed a distinct peak deceleration of the knee joint during the eccentric phase and a peak acceleration of the knee joint during the concentric phase near joint reversal, depicting coupling time. APPLICATION: Defining coupling time as the difference between the peak eccentric and concentric phase knee angular accelerations is an effective method which can be utilized in future SSC jump studies. The findings demonstrate that contact time can be used to predict coupling time, thus providing trainers with the opportunity to use a force plate or contact mat to estimate coupling time in evaluating athletes. Furthermore, the study observed unique changes in the angular acceleration of the knee joint during a slow SSC jump. This finding adds to our knowledge of the SSC, but still raises further questions to its explanation it in terms of joint moments. On the other hand, this information can be immediately important in the modern training setting. Understanding that a decreased level of angular acceleration occurs throughout the reversal of the knee joint motion during a slow SSC jump, directs trainers to eliminate or minimize this in their athletes, with the goal of creating a more effective SSC.