Changes in joint, muscle, and tendon stiffness following repeated hopping exercise

Abstract

The purpose of this study was to elucidate the mechanisms of decline in joint stiffness after repeated stretch‐shortening cycle exercises according to changes in both muscle‐tendon properties and neuromuscular activities. Eleven males performed fatigue task (5 sets of 50 hopping). Ankle joint stiffness and electromyographic activities (mEMG) of plantar flexor and tibial anterior muscles during drop jump were measured before and after fatigue task. Active muscle stiffness with (100 deg·sec−1) and without (250 deg·sec−1) stretch reflex were calculated according to changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions. Tendon stiffness was measured during ramp and ballistic contractions. After fatigue task, joint stiffness significantly decreased by 20.7 %, whereas mEMG of measured muscles during drop jump did not. After fatigue task, active muscle stiffness with and without stretch reflex significantly decreased by 15.7 % and 21.5 %, and tendon stiffness measured during ramp and ballistic contractions did not change. In addition, the relative change in joint stiffness was significantly correlated with that in active muscle stiffness with stretch reflex (r = 0.737, P = 0.009), but not with those in the other measured variables. These results suggested that the decline in joint stiffness after repeated hopping exercises would be caused by changes in active muscle stiffness, but not those in tendon properties or neuromuscular activities.

Medial Gastrocnemius Muscle Architecture Is Altered After Exhaustive Stretch-Shortening Cycle Exercise

“…Indeed, Kubo and Ikebukuro (2019) have recently reported a large reduction in the amount of MG fascicle shortening during the braking phase of ankle-joint only DJs after repeated hopping. In particular, at group level the fascicles showed an initial stretch immediately after ground contact ( Figure 1B in Kubo and Ikebukuro, 2019), demonstrating potential for fascicles to be exposed to greater strain as the exercise protocol proceeded. Greater fascicle strain as the exercise task progressed would have led to muscle damage (Lieber and Fridén, 1993;Peñailillo et al, 2015) that has previously been reported after similar fatigue protocols (Miyama and Nosaka, 2004;Ishikawa et al, 2006;Dousset et al, 2007).…”

“…Briefly, the formula accounts for the perpendicular ground reaction force, the estimated length between the center of the ankle joint (center of the lateral malleolus) and the ball of the foot, and the ankle joint angle at the lowest point (transition from braking to propulsion phase). Ankle joint stiffness was calculated as the change in ankle joint moment divided by the change in ankle joint angle during the braking (eccentric) phase (Kuitunen et al, 2002;Kubo and Ikebukuro, 2019).…”

“…The increased range of motion at the ankle, but not knee, joint during DJ after exercise resulted in a greater stretch of the MG MTU during the braking phase. Because Achilles tendon mechanical properties are typically unchanged after prolonged SSC exercise (Peltonen et al, 2010(Peltonen et al, , 2012Lichtwark et al, 2013;Kubo and Ikebukuro, 2019), this likely resulted in changes at the muscle fascicle level. In non-fatigued conditions, MG fascicles generally shorten before operating quasi-isometrically or minimally stretching during DJs from the optimal dropping height, but undergo a larger stretch during DJs from heights greater than optimal (Ishikawa et al, 2005;Sousa et al, 2007).…”

“…In non-fatigued conditions, MG fascicles generally shorten before operating quasi-isometrically or minimally stretching during DJs from the optimal dropping height, but undergo a larger stretch during DJs from heights greater than optimal (Ishikawa et al, 2005;Sousa et al, 2007). Indeed, Kubo and Ikebukuro (2019) have recently reported a large reduction in the amount of MG fascicle shortening during the braking phase of ankle-joint only DJs after repeated hopping. In particular, at group level the fascicles showed an initial stretch immediately after ground contact ( Figure 1B in Kubo and Ikebukuro, 2019), demonstrating potential for fascicles to be exposed to greater strain as the exercise protocol proceeded.…”

“…Because the SSC sequence occurs in many common activities, such as running and jumping, repetitive SSC exercise better represents naturally occurring fatigue compared to repetitive isolated isometric, concentric, or eccentric tasks (Komi, 2000;Nicol et al, 2006). Although fatiguing SSC exercise has been reported to alter MG (Lidstone et al, 2016;Kubo and Ikebukuro, 2019) and soleus (Ishikawa et al, 2006) muscle architecture, neither study took measures during MVC immediately post-exercise. Further, while there was increased length of soleus fascicles at rest following SSC exercise (Ishikawa et al, 2006), to our knowledge there are no data available regarding fatigue-related changes in resting MG muscle architecture after SSC exercise.…”