Differences in properties of the triceps surae muscle-tendon unit in Maasai jumpers and Caucasian controls during repetitive jumping

Abstract

Purpose. The present study examined the anthropological features in ten Maasai males and investigated their muscle-tendon unit (MTU) function during repetitive jumping via fascicle behavior. The obtained data was compared to a group of six Caucasian males. Methods. Ultrasonography, kinematics, kinetics and electromyography (EMG) data was recorded during two conditions; submaximal and maximal repetitive jumping. Results. The Maasai jumpers had a longer Achilles tendon and foot than the Caucasian controls. During both conditions of repetitive jumping the Maasai jumpers had a lower jumping frequency, longer contact time, and a larger range of motion (ROM) of both the ankle, knee and hip than Caucasian controls. From submaximal to maximal condition frequency decreased, flight time was longer, and angular ROM increased for both groups. Fascicle behavior during ground contact was generally isometric for both groups, and the fascicle length of Maasai jumpers was shorter than that of Caucasian controls. The muscle-tendon unit (MTU) of both groups demonstrated a classical stretch-shortening cycle behavior during ground contact. The gastrocnemius medialis (GM) MTU length change and GM tendinous tissues length change was larger for the Maasai jumpers during both conditions compared to Caucasian controls. GM MTU length change was larger in maximal compared to submaximal condition for both groups. The EMG activation pattern of GM, SOL and VL was different between Maasai jumpers and Caucasian controls. Conclusion. This study on Maasai jumpers revealed that they have optimized a jumping technique with a longer contact time and a larger ROM of the ankle, knee and hip than Caucasian controls. As a result of larger angular ROM the Maasai jumpers had a larger stretch of GM MTU and GM tendinous tissues. The longer AT and foot of the Maasai jumpers correlated weakly to jumping performance.