Muscle–tendon properties of the female athlete: a comparison between “power modulation” and “energy conservation” training exposures

Muscle-tendon function can be categorised into "energy conservation" or "power modulation" tasks. However, little is known about how female tendons adapt to these different loading demands. This study compared muscle-tendon unit morphological and mechanical properties in athletes who regularly undergo either energy conservation (14 runners) or power modulation (eight netballers) activities. Static ultrasound was used to measure Achilles' and patellar tendon thickness, as well as the thickness, pennation angle, and fascicle length of the gastrocnemii and vastus lateralis muscles. Achilles' tendon length and moment arm were also measured. Muscle-tendon mechanical measures included plantar flexion and knee extension isometric strength, and Achilles' tendon elongation, strain, and stiffness. Netballers displayed significantly higher absolute tendon thickness (p = 0.004 for Achilles', p = 0.021 for patellar), but not when normalised to body mass. Netballers also displayed significantly higher Achilles' tendon stiffness (p = 0.046) and isometric plantar flexion and knee extension strength (both p < 0.001). No differences were detected in any other measure of muscle or tendon morphology. The results of this study provide evidence that power modulation activities promote different muscle-tendon unit properties to energy conservation activities in females, but that these adaptations may be body mass dependent.