Loading the Limb During Rhythmic Leg Movements Lengthens the Duration of Both Flexion and Extension in Human Infants

Abstract

Musselman KE, Yang JF. Loading the limb during rhythmic leg movements lengthens the duration of both flexion and extension in human infants. J Neurophysiol 97: 1247J Neurophysiol 97: -1257J Neurophysiol 97: , 2007. First published December 6, 2006; doi:10.1152/jn.00891.2006. Sensory input is critical for adapting motor outputs to meet environmental conditions. A ubiquitous force on all terrestrial animals is gravity. It is possible that when performing rhythmic movements, animals respond to loadrelated feedback in the same way by prolonging the muscle activity resisting the load. We hypothesized that for rhythmic leg movements, the period (extension or flexion) experiencing the higher load will be longer and vary more strongly with cycle period. Six rhythmic movements were studied in human infants (aged 3-10 mo), each providing different degrees of load-related feedback to the legs during flexion and extension of the limb. Kicking in supine provided similar loads (inertial) during flexion and extension. Stepping on a treadmill, kicking in supine against a foot-plate, and kicking in sitting loaded the legs during extension more than flexion, whereas air-stepping and air-stepping with ankle weights did the opposite. Video, electrogoniometry, surface electromyography, and contact forces were recorded. We showed that load-related feedback could make either the duration of flexion or extension longer. Within the tasks of stepping and kicking against a plate, infants who exerted lower forces showed shorter extensor durations than those who exerted higher forces. Because older babies tend to step with greater force, we wished to rule out the contribution of age. Eight babies (Ͼ8 mo old) were studied during stepping, in which we manipulated the amount of weightbearing. The same effect of load was seen. Hence, the degree of loading directly affects the duration of extension in an incremental way.

Modulation of phase durations, phase variations, and temporal coordination of the four limbs during quadrupedal split-belt locomotion in intact adult cats

“…However, when the hindlimbs were loaded, r EXT increased considerably while r FLEX went toward 0. Similar results were found in human infants when loading was applied to the legs in a variety of actual rhythmic movements (Musselman and Yang 2007). Thus stance-related inputs (i.e., force, stretch of ankle extensors, and/or pressure to the plantar surface) can considerably modify the regulation of phase durations and variations.…”

Fast Locomotor Burst Generation in Late Stage Embryonic Motility

“…6) were similar to those reported for walking in hatchlings, although modest positive correlations were reported for swimming and walking (Johnston and Bekoff 1996). TA burst duration does not typically follow changes in locomotor cycle duration (Grillner 1981) but can vary with cycle duration when a mechanical load is applied to ankle dorsiflexors during stepping (Musselman and Yang 2007). Thus TA burst frequency and duration during RLMs appeared to be controlled in a manner consistent with muscle activity controlled by a locomotor burst generator.…”

A novel approach to mechanical foot stimulation during human locomotion under body weight support

“…There are controversial data in the literature concerning the effect of foot loading on the cycle duration and walking speed. For instance, Stephens and Yang (1999) found that loading during the stance phase of walking in adults increases the extensor EMG amplitude but does not change the duration of the step cycle (see also Misiaszek, Stephens, Yang, and Pearson (2000)), while a large change in timing was seen in the infants (Musselman & Yang, 2007). Furthermore, the changes in duration of phases may be more prominent in reduced preparations than in intact animals (Duysens & Stein, 1978;Stephens & Yang, 1999;Whelan & Pearson, 1997).…”

“…Moreover, the ability of any single input to entrain or affect the locomotor rhythm is much reduced when competing with the input from other afferents and descending pathways (Ivanenko, Grasso, & Lacquaniti, 2000;Stephens & Yang, 1999;Whelan & Pearson, 1997). A current view on the role of different mechanoreceptors considers task-and context-dependent contribution of sensory inputs (Pearson, 2004), as well as its maturation in early development (Dominici, Ivanenko, & Lacquaniti, 2007;Musselman & Yang, 2007). In addition, the organization of the interneuronal network for locomotion and the use of corrective reactions during walking points toward a rule-based finite control system rather than a simple additive principle of multisensory fusion (Misiaszek, 2006;Prochazka, 1996).…”