Abstract
Children who idiopathically toe‐walk (ITW) habitually operate at greater plantarflexion angles and thus, at shorter muscle‐tendon unit (MTU) lengths than typically developing (TD) children. Therefore, it is often assumed that habitual use of the gastrocnemius muscle in this way will cause remodelling of the muscle‐tendon architecture compared to TD children. However, the gastrocnemius muscle architecture of children who ITW has never been measured. It is essential that we gain a better understanding of these muscle‐tendon properties, to ensure that appropriate clinical interventions can be provided for these children. Five children who ITW (age 8 ± 2 years) and 14 TD children (age 10 ± 2 years) participated in this study. Ultrasound was combined with isokinetic dynamometry and surface electromyography, to measure muscle architecture at common positions and passive lengthening properties of the gastrocnemius muscle and tendon across full range of motion. Regardless of which common condition groups were compared under, both the absolute and normalised to MTU muscle belly and fascicle lengths were always longer, and the Achilles tendon length was always shorter in children who ITW than TD children (p < 0.05; large effect sizes). The passive lengthening properties of the muscle and tendon were not different between groups (p > 0.05); however, passive joint stiffness was greater in children who ITW at maximum dorsiflexion (p = 0.001) and at a joint moment common to all participants (p = 0.029). Consequently, the findings of this pilot study indicate a remodelling of the relative MTU that does not support the concept that children who ITW commonly experience muscle shortening. Therefore, greater consideration of the muscle and tendon properties are required when prescribing clinical interventions that aim to lengthen the MTU, and treatments may be better targeted at the Achilles tendon in children who ITW.
Highlights
Across the full range of motion (ROM), children who idiopathically toe-walk (ITW) had longer muscle and fascicle lengths and a shorter tendon length than typically developing (TD) children (Figure 3). These differences were statistically significant when groups were compared at a common joint angle (−15°), common muscle-tendon unit (MTU) length (365 mm) and at individual 0 Nm (Table 1), despite children who ITW being significantly more plantarflexed than TD children (p = 0.016)
Fascicle length normalised to MTU length was significantly longer in children who ITW than TD children in all considered joint positions (p < 0.05; large effect size (ES): 2.16–3.27) (Table 1)
In all considered joint positions, children who ITW had longer absolute and normalised gastrocnemius medialis muscle belly and fascicle lengths, and a shorter Achilles tendon length than TD children, despite habitually operating at shorter MTU lengths. These findings indicate a remodelling of relative MTU lengths, which does not support the concept that these children commonly experience muscle shortening caused by a reduced ROM, as children with cerebral palsy (CP) do
Summary
The aim of this study was to measure the architectural structure and passive lengthening properties of the gastrocnemius medialis muscle and Achilles tendon in children who ITW and TD children across the ROM
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