Anticipation of drop height affects neuromuscular control and muscle‐tendon mechanics

Abstract

This study examined the effect of drop height on neuromechanical control of the plantarflexors in drop jumps (DJs) before and during ground contact (GC). The effect of anticipation on muscle mechanical configurations was investigated in 22 subjects in three conditions (20, 30, and 40 cm): (i) known, (ii) unknown, or (iii) cheat falling heights (announced 40 cm, but actual drop height was 20 cm). Electromyographic (EMG) activity of the m. gastrocnemius medialis (GM) and other shank muscles was recorded and analyzed before GC and during GC separately for the short-, medium-, and long-latency responses (SLR, MLR, and LLR). Changes in GM fascicle length (L M ) were determined via B-mode ultrasound, and muscle-tendon unit length (L MTU ) was estimated. Peak force (P < .001), rate of force development (RFD) (P = .001) and GM EMG activity prior to (P = .003) and during GC (P = .007) was reduced in the unknown compared with the known conditions (P < .05). The amount of shortening in L MTU during GC in unknown and cheat was less compared with the known conditions (P = .005; P = .049). Changes in L MTU lengthening negatively correlatedwith changes in GM activity around SLR and MLR (P = .006; P = .02) in known and unknown conditions. Taken together, it seems that the central nervous system applies a protective strategy in the unknown condition by reducing muscle activity to result in a lower muscular stiffness and increased tendinous lengthening prior to and during GC. This might be a mechanism to absorb greater elastic energy in the tendon and reduce the magnitude and rate of muscle lengthening and subsequent stretch-induced muscle damage.

Association and Agreement between Reactive Strength Index and Reactive Strength Index-Modified Scores

“…Pre-activation increases the stiffness of skeletal muscle and, when impact forces are predicted correctly, facilitates a safe dispersion of stress through the muscle-tendon complex upon landing [ 22 ]. Pre-activation may also enhance the SSC response to landing impact by preparing the muscle-tendon complex to store elastic energy and by modifying the short latency spinal reflex via input from supraspinal drive and alpha-gamma co-activation [ 7 , 22 , 47 , 48 ].…”

“…Several authors have acknowledged the pre-activation of skeletal muscle as a fundamental component of natural, or functional, lower-extremity SSC actions [ 48 , 49 , 50 ]. For example, to evaluate functional lower-extremity SSC utilization, Nicol et al [ 49 ] recommend the performance of jumping techniques, such as DJ, that involve a rapid stretch of pre-activated skeletal muscle.…”

The Anticipation of Gravity in Human Ballistic Movement

“…Increased flexion is described as an efficient knee motion strategy to compensate high joint loads. Mechanically, these adaptations result in loss of reactive performance (Gollhofer and Kyröläinen, 1991;Avela et al, 1996;Kramer et al, 2012;Helm et al, 2019Helm et al, , 2020.…”

Skeletal Muscle Shape Change in Relation to Varying Force Requirements Across Locomotor Conditions

“…The strains we recorded for the rat Achilles tendon in vivo match well with the data from recent materials testing of the same tendon (Javidi et al, 2019). Because MG fascicle strains showed little evidence of net lengthening across all gait-slope conditions, energy stored in the MG tendon during force development is presumably recovered to power limb and body movement, rather than being dissipated by doing work on the muscle (via fascicle stretch; i.e., "elastic backfire"; sensu (Roberts and Azizi, 2011); in contrast to the buffering of rapid stretch and energy absorption observed for turkey landings from drops of different heights and for landings from human jumps (Werkhausen et al, 2017;Werkhausen et al, 2018;Helm et al, 2019;Hollville et al, 2019).…”

“…When humans and other animals decelerate or move downhill, the function of limb muscles, as a whole, must shift toward eccentric contractions to absorb energy, braking the body's motion (Gabaldon et al, 2004;Ishikawa and Komi, 2004;Lichtwark and Wilson, 2006;Biewener and Daley, 2007;Helm et al, 2019). By contrast, when the locomotor task is to accelerate, move uphill, or climb stairs, muscles of the limbs must shift toward concentric contractions to generate greater net positive work (Gillis and Biewener, 2002;Daley and Biewener, 2003;Gabaldon et al, 2004;Hoyt et al, 2005;McGuigan et al, 2009).…”