Muscle contractile properties as an explanation of the higher mean power output in marmosets than humans during jumping

The muscle mass specific mean power output (P_MMS,mean) during push-off in jumping is in marmosets (Callithrix jacchus) more than twice that in humans. In the present study it was tested whether this is attributable to differences in muscle contractile properties.

In biopsies of marmoset m. vastus lateralis (VL) and m. gastrocnemius medialis (GM) (n=4) fiber type distribution was assessed using fluorescent immunohistochemistry. In single fibers from four marmoset and nine human VL biopsies the force-velocity characteristics were determined.

Marmoset VL contained almost exclusively fast muscle fibers (>99.0%), of which 63% were type IIB and 37% hybrid fibers, fibers containing multiple myosin heavy chains. GM contained 9% type I fibers, 44% type IIB and 47% hybrid muscle fibers. The proportions of fast muscle fibers in marmoset VL and GM were substantially larger than those reported in the corresponding human muscles. The curvature of the force-velocity relationships of marmoset type IIB and hybrid fibers was substantially flatter than that of human type I, IIA, IIX and hybrid fibers resulting in substantially higher muscle fiber mass specific peak powers (P_FMS,peak). Muscle mass specific peak power output (P_MMS,peak) of marmoset whole VL and GM, estimated from their fiber type distributions and force-velocity characteristics were more than twice the estimates for the corresponding human muscles.

Since the relative difference in estimated P_MMS,peak between marmoset and human is similar to that P_MMS,mean during push-off in jumping, it is likely that the difference in in vivo mechanical output between humans and marmosets is attributable to differences in muscle contractile properties.