The Effects Of Muscle-Tendon Length Change During A Fatiguing Hopping Protocol On Time To Exhaustion

Background: Previous research studies conclude that exhaustive stretch-shortening cycle (SSC) exercise has induced in vivo length changes in muscular architecture. Literature has also proven that muscle architectural changes from fatiguing SSC activities results in a loss of ability to store elastic energy for exercise performance and may increase contractile component(CC)length. However, it is unclear if these neuromuscular adaptations are an altered response to the already occurring changes in muscular architecture during repetitive,exhaustive SSC exercise, and whether or not these changes are inducing alterations in total time to exhaustion (TTE). The purpose of this study was to use an exhaustive SSC task to understand the correlations between changes in length of the muscular architecture with the onset of fatigue, and to determine how these length changes relate to TTE. Plantarflexor (PF) and dorsiflexor (DF) CC length, muscle thickness, and pennation angle changes were examined. Methods: Eight college-aged males participated in an exhaustive single-joint hopping task to fatigue. At different time-points, motion capture data of the hopping kinetics and kinematics, and medial gastrocnemius (MG) muscle activity were collected, as well as in vivo ultrasound data of the MG. TTE was defined as the total time each subject was able to continuously hop. Results: CC lengths were found to significantly increase as subjects approached exhaustion. With significant correlations of p=0.01 correlational relationships to percent changes in muscle thickness (r=0.87; p=0.005 and pennation angle (r= 0.94; p=0.000) were noticed when compared to TTE. Conclusion: Findings from the current study suggest that changes in CC muscle lengths, occurring during repetitive hopping to exhaustion,will increase as subjects approach fatigue. Furthermore the amounts of CC length change, as well as, changes in pennation angle and muscle thickness were strongly related to TTE