After talking briefly about muscle stretch shortening in class, I thought this was an interesting topic and looked into some literature to better understand what is going on. I found a study that focused on upper-body explosive movements, and how load and stretch shortening cycles (SSC) affect the kinematics, kinetics, and muscle activation that occur. This was an interesting study because they looked at maximal effort bench throws, where much of the previous research focused only on lower-extremity exercises. Each subject performed an SSC throw and concentric only throws, comparing displacement, velocity, acceleration, force, power output and EMG from the pectoralis major, anterior deltoid, and triceps brachii. SSCs are usually performed before explosive movements (e.g. throwing, jumping) which lengthen the muscle preparing to contract to ensure maximal velocity is reached during the movement. When the muscle lengthens, elastic energy is stored which can then be released during the movement, however, if the time between lengthening and contracting is too long, the energy dissipates, leading to a slower contraction with less power.

As expected, the average velocity was lower for the concentric only throws when compared to the SSC throws, however, there was no difference in throw height between the two groups. Average and peak force and power output were both higher for the SSC through compared to the concentric only throw. The findings from this study agree with findings from previous studies focusing on vertical jump, showing that similar muscle kinetics are at play. Muscle kinetics are an extremely interesting area of study, and even though we only briefly discussed muscle length-tension, force-velocity, and power relationships in class, this is a huge field of study. Some groups choose to look at specific muscle groups, while others look at more complex movements that require multiple groups of muscles to be activated. This area of research has led to improvements in stretching suggestions for athletes; stretching before performing explosive movements is not actually as beneficial as we once thought. Stretching the muscle allows for elastic energy dissipation, instead of storing the energy for immediate release. However, stretching is still extremely beneficial after workouts, helping to prevent muscle soreness and excess inflammation. Additionally, there are some chronic adaptations to stretching including increasing flexibility for a wider range of motion during typical daily activities as well as athletic endeavors.

References:

1. Newton, R. U., Murphy, A. J., Humphries, B. J., Wilson, G. J., Kraemer, W. J., & Häkkinen, K. (1997). Influence of load and stretch shortening cycle on the kinematics, kinetics and muscle activation that occurs during explosive upper-body movements. European Journal of Applied Physiology and Occupational Physiology, 75(4), 333–342. https://doi.org/10.1007/s004210050169
2. Bosco, Carmelo, and Paavo V. Komi. (1979) Mechanical characteristics and fiber composition of human leg extensor muscles. European journal of applied physiology and occupational physiology4 (1979): 275-284.