Stretching has become a routine part of almost all athletes’ pre-training warm up to improve performance and decrease the risk of injury (Perrier et al., 2011; Young and Behm, 2003). The believed benefits of stretching are thought to be achieved by increasing muscle temperature, increasing neural activation, and reducing musculotendinous stiffness (Young and Behm, 2003). Most warm-ups will include a low-intensity aerobic component, stretching of relevant muscles, and some rehearsal of the activities that will be performed. While the use of a warm-up prior to maximum effort explosive exercise (sprinting, jumping etc.) is rarely questioned, the protocol leading to optimum performance remains a topic of debate.
Most research indicates that a comprehensive warm-up should include both general and specific preparation. The general warm-up should increase core and muscle temperature and range of motion. The specific portion of a warm-up should reinforce the movement and motor patterns of the activity that follows, as explosive and dynamic movements require high levels of neuromuscular activation and optimal musculotendinous stiffness (Sotiropoulos et al., 2010). The stretch-shortening cycle (SSC) is the “pre-stretch” or countermovement that can be seen in movements like walking, running, and jumping. This pre-stretch allows the athlete to produce more force move quicker.
Therefore, it may be beneficial to include more dynamic movements in the general and specific warm-up to prepare the neuromuscular system for the intense activity utilizing the SSC rather than static stretching which is less transferrable to the requirements of the explosive movements in the activity that will follow.
Static stretching has been shown to increase acute range of motion at the joint being stretched, however research has shown it decreases the strength and power outputs of these muscles (Simic et al., 2013). Further, stretching alone has not been shown to reduce injury risk (Shrier, 2001). Because it seems that static stretching decreases maximal force production, jump height, and sprint speed, while increasing reaction time and impairing balance (Perrier et al., 2013), there has been a shift away from pre-training static stretching in favor of a more functional dynamic warm-up.
The exact mechanism that leads to reduced performance after static stretching remains unclear, but it is likely due to both mechanical and neural factors. After stretching, contractile units must contract more rapidly over a greater distance, likely increasing the time needed to produce a given amount of force. Neurologically, static stretching seems to decrease motor unit activation as a result of inhibitory mechanisms involved with lengthening the muscle point (Perrier et al., 2013).
Dynamic stretching incorporates low-intensity aerobic activity such as skipping, jogging, or shuffling of increasing intensity to replicate the movement patterns about to be performed. Dynamic stretching is as effective in increasing joint range of motion but because it is more active in nature, it could improve performance by rehearsing the movement patterns to be used and increasing blood flow to the muscles (resulting in increased oxygen delivery and waste removal) (Perrier et al., 2013). Dynamic stretching increases the number of firing motor units and may cause the facilitation of the stretch reflex which could help prime the nervous system for more intense activity (Kirmizigil et al., 2014).
Because successful performance in sport or maximum effort jumping, throwing, and sprinting, the activity and specificity of dynamic warm-ups are thought to be more effective at improving performance in such activities (Kirmizigil et al., 2014). Young and Behm found that a dynamic style warm-up including general, submaximal aerobic activity had a positive influence on muscle performance in jump height compared to static stretching alone. Jump height was further increased after a protocol of general submaximal aerobic activity was followed by the skill that was about to be performed (jumping) at gradual increasing intensity (Young and Behm, 2003). Therefore, a well-designed warm-up should include both general preparation as well as movement- or sport-specific rehearsal to optimally prepare the athlete for peak performance.
The Stretch-Shortening Cycle (SSC)
The stretch-shortening cycle (SSC) is the countermovement action that can be seen in movements such as walking, running, and jumping. Athletes have been shown to jump 2-4 cm higher using a countermovement when jumping than during a squat jump with no countermovement (Bobbert and Casius, 2005). There is some debate as to the mechanisms responsible for the performance improvements using the SSC, however ensuring the body’s neuromuscular system is primed using a thorough dynamic warm-up that incorporates elements specific to the activity that will follow can contribute to optimized performance and increased jump height. Some of the neurophysiological mechanisms that contribute to the SSC include the storage of elastic energy, involuntary nervous processes, active state, length-tendon characteristics, and motor coordination (Walker, 2016).
The SSC is a cyclical muscle action composed of an eccentric, amortization (transitional period), and concentric phase and can be described as a spring-like mechanism (Lloyd et al., 2012). Compressing the spring will cause the coil to rebound and jump off the surface and increasing the speed at which it is pressed, or the amount of force applied will result in a jump of greater magnitude. Therefore, a jump using a countermovement will often allow the athlete to jump higher or farther than a jump from a static position (McBride et al., 2008).
Electromechanical Delay (EMD)
Electromechanical delay (EMD) refers to the neural and physiological delay in the production of force (Walker, 2016). This means the muscle cannot transmit force instantaneously but this delay in force production can lead to a reduction in performance. Some factors that may contribute to this delay include:
- Finite rate in muscle stimulation by the CNS
- Propagation of the action potential on the muscle membrane
- Time-constraints of calcium release and cross-bridge formation
- Interaction between contractile filaments
Optimizing muscular pre-activity has been shown to reduce or counteract the effects of EMD by exciting the muscle and creating musculotendinous stiffness prior to the start of the SSC (Turner and Jeffreys, 2010). Because of the detrimental effects of EMD on force production, the completion of a proper warm-up will optimize the SSC, reduce the effects of EMD, and allow the athlete to perform optimally.
- Static stretching has been shown to increase acute joint range of motion but decrease strength and power output.
- Dynamic stretching increases range of motion, rehearses movement patterns, increases blood flow and prepares the nervous system for more intense activity.
- Performance increases when the warm-up is specific to the activity to be performed.
- The stretch-shortening cycle (SSC) is the countermovement action that can be seen in movements such as jumping.
- Electromechanical delay (EMD) is detrimental to force production but can be minimized or negated by properly preparing the body with a specific warm-up for the optimization of the SSC.
- Perrier ET, Pavol MJ, Hoffman MA. The acute effects of a warm-up including static or dynamic stretching on countermovement jump height, reaction time, and flexibility. J Strength Cond Res. 2011 Jul;25(7):1925-31. doi: 10.1519/JSC.0b013e3181e73959. PMID: 21701282.
- Young WB, Behm DG. Effects of running, static stretching and practice jumps on explosive force production and jumping performance. J Sports Med Phys Fitness. 2003 Mar;43(1):21-7. PMID: 12629458.
- Sotiropoulos, K., Smilios, I., Christou, M., Barzouka, K., Spaias, A., Douda, H., & Tokmakidis, S. P. (2010). Effects of warm-up on vertical jump performance and muscle electrical activity using half-squats at low and moderate intensity. Journal of sports science & medicine, 9(2), 326–331.
- Simic, L., Sarabon, N. and Markovic, G. (2013), Acute static stretching and performance. Scand J Med Sci Sports, 23: 131-148. doi:10.1111/j.1600-0838.2012.01444.x
- Shrier I. Should people stretch before exercise?. West J Med. 2001;174(4):282-283. doi:10.1136/ewjm.174.4.282
- Kirmizigil B, Ozcaldiran B, Colakoglu M. Effects of three different stretching techniques on vertical jumping performance. J Strength Cond Res. 2014 May;28(5):1263-71. doi: 10.1519/JSC.0000000000000268. PMID: 24755866.
- Bobbert MF and Casius LJ. Is the countermovement on jump height due to active state development? Med Sci Sport Exerc 37: 440–446, 2005.
- Walker, O. (2016, January 23). Stretch-Shortening Cycle. Retrieved November 01, 2020, from https://www.scienceforsport.com/stretch-shortening-cycle/
- Lloyd, R.S., Oliver, J.L., Hughes, M.G., and Williams, C.A. (2012). The effects of 4-weeks of plyometric training on reactive strength index and leg stiffness in male youths. Journal of Strength and Conditioning Research, 26(10), pp.2812–2819.
- McBride JM, McCaulleyGO, and Cormie P. Influence of preactivity and eccentric muscle activity on concentric performance during vertical jumping. J Strength Cond Res 23: 750–757, 2008.
- Turner, A.N., Jeffreys, I. (2010). The stretch-shortening cycle: proposed mechanisms and methods for enhancement. Journal of Strength and Conditioning Research, 17, 60-67.