The Use of Contact Time and the Reactive Strength Index to Optimize Fast Stretch-Shortening Cycle Training

Abstract

Lead Summary 6This article reviews research relating to the stretch shortening cycle and plyometrics. 7The article introduces strength and conditioning practitioners to using ground contact 8 times and the reactive strength index in plyometric training. It documents how these 9 measurements can be used to optimize plyometrics and improve athletes' fast stretch 10 shortening cycle performance. Recommendations are made regarding the use of ground 11 contact times to improve training specificity and the use of the reactive strength index to 12 optimize plyometrics, to monitor training progress and as a motivational tool. A four step 13 progression of implementation, previously used with elite rugby players is detailed. 15The Stretch Shortening Cycle 16The stretch-shortening cycle (SSC) is a natural type of muscle function in which muscle 17 is stretched immediately prior to being contracted. This eccentric/concentric coupling of 18 muscular contraction produces a more powerful contraction than that which would result 19 from a purely concentric action alone (14). When the force velocity curve is measured 20 during a complex SSC movement involving a number of joints and muscle groups, such 21 as a vertical jump, the utilization of a preceding eccentric phase shifts the force-velocity 22 curve to the right. In comparison with purely concentric movements, the SSC allows 23 higher forces to be produced at any given velocity during the concentric phase (13). 25The SSC is observed in a wide range of activities. In real life situations, exercise seldom 31One view has been that the SSC causes an enhancement during the concentric phase 32 due to the storage and reutilization of elastic energy (7;16

Análise biomecânica da fase de contato no salto em profundidade no solo e na água

“…In this context, it is possible that the aquatic environment, by significantly reducing load during the braking phase, does not provide adequate stimulus for the effective development of SSC. However, lower drop heights and less intense loads are preferable in the initial stages of adaptation to training and increases must be gradual 16 . Additionally, the load reduction during braking sub-phase in water can be one of the reasons for lower levels of delayed onset muscle soreness 23 and / or the lower concentration of muscular stress markers 9 reported in literature for individuals who perform aquatic plyometric training compared to those who perform ground plyometric training.…”

“…However, although the reduction of loads during landing of jumps is considered beneficial, when it comes to the risk of injury, water resistance can compromise the goals of plyometric training, since the duration of the contact phase is likely to be higher compared to exercises performed on dry land, and consequently the transition speed between eccentric and concentric actions will be lower. For the elastic energy stored during SSC eccentric action to be optimally used and the stretch reflex to be efficiently activated, resulting in an enhancement of subsequent concentric action; this transition should take place as soon as possible 1,16,17 . At hip water immersion, it is likely that this condition is not satisfied due to the effect of water physical properties on the temporal characteristics of movement, which in turn could lead to inefficient functioning of SSC.…”

“…Since drop jump (DJ) is one of the exercises most widely used in plyometric training [16][17][18] , this study aimed to analyze and compare the vertical component of the ground reaction force and contact duration of DJ performed at hip immersion in water and on dry land.…”

Influence of body composition on selected jump performance measures in collegiate female athletes

“…1,2,3 Additionally, vertical jump testing is reliable and valid in its estimation of explosive muscular power, 4 power development, 5 and as an indicator of performance. 6 Two primary jumps utilized to measure athletes' jumping ability are the squat or static jump (SJ) and countermovement vertical jump (CMJ). The SJ assesses lower-body concentric strength and power while the CMJ can assess lower-body reactive strength and power (SSC incorporation).…”

An Investigation Into the Recovery Process of a Maximum Stretch-Shortening Cycle Fatigue Protocol on Drop and Rebound Jumps

“…The RSI has been defined as the ability to change quickly from an eccentric to a concentric contraction; it is calculated by dividing the height jumped by the CT (38). The RSI is relatively simple to determine in applied settings and, therefore, has been frequently used by practitioners (18,31) and researchers (38) to monitor an individual's SSC abilities. Recent studies have examined the relationship between SSC performance, muscle stiffness, and the response of these factors to acute bouts of fatiguing exercise.…”