The study demonstrates specific biochemical adaptations in the limb myofibres of the five-toed jerboa that support its intensive bipedal hopping locomotion.
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Reveals locomotor muscle specialization in rodents; hypothesis-generating for human gait disorders with no immediate clinical implications.
Biochemical adaptations of limb myofibres to intensive bipedal hopping were investigated using the five-toed jerboa Allactaga elater as a model in comparison with the rat. Immunofluorescence methods included immunoreactivity to anti-fast and anti-slow MHC and troponin I. There is no specialization of triceps caput mediale for postural function in the minute non-locomotor forelimbs, unlike quadruped mammals. The various elbow extensor heads and the flexor muscles are alike with regard to fibre type population and cross-sectional areas of each type of fibre. The extensor muscle in the elongated hindlimbs of the five-toed jerboa, at both the knee and the ankle joints, differ from each other extensively. One head, made up of an extremely high percentage of type I, fatigue-resistant fibres, is suited to postural function. Two extensor heads at each joint contain a very high percentage of type IIB fibres (having the greatest maximal velocity of contraction) and are able to produce the powerful acceleration needed to trigger the leap. The relative cross-sectional areas of the myofibres are characteristic of hopping locomotion: predominance in number of one type of myofibre in a muscle accompanies greater cross-sectional area, which increases muscle efficiency in either postural or accelerative function of the muscle.
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Jouffroy et al. (2003) studied this question.
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