Plantar intrinsic foot muscle activity and its relationship with postural sway during tiptoe standing in ballet dancers and non-dancers.

BACKGROUND: Minimizing postural sway during tiptoe standing is essential for ballet dancers. Investigation of the activity of the plantar intrinsic foot muscles (PIFMs) may provide insight into postural sway in dancers. Herein, we compared PIFM activity during tiptoe standing between dancers and non-dancers and examined its relationship with postural sway. METHODS: We enrolled 14 female ballet dancers and 13 female non-dancers. Electromyography (EMG) amplitudes of 64 channels of PIFMs and center of pressure (COP) data were recorded during bipedal tiptoe standing tasks performed with ankle plantarflexion angles of 20°, 40°, and 60° (dancers only). The EMG amplitudes were normalized to those during the maximum voluntary contraction, and the muscle activity level and its coefficient of variation over time (EMG-CVtime) during the task were assessed. Standard deviations in the anteroposterior and mediolateral directions, velocity, and area were calculated from the COP data. RESULTS: Most COP and EMG variables were significantly lower in dancers than in non-dancers in both the 20° and 40° tasks (p < 0.05). Significant correlations were found between most combinations of the COP and EMG variables in both the 20° and 40° tasks in the whole cohort (r = 0.468-0.807, p ≤ 0.014). In the 60° task in dancers, COP velocity was strongly correlated with EMG-CVtime (r = 0.700, p = 0.005). CONCLUSION: These results provide novel evidence that the PIFMs do not require high activity, but rather that its low, steady activity is the key, to achieve less postural sway during bipedal tiptoe standing in dancers.

Triceps surae muscle hypertrophy is greater after standing versus seated calf-raise training.

Background: The triceps surae muscle plays important roles in fundamental human movements. However, this muscle is relatively unresponsive to resistance training (difficult to hypertrophy) but prone to atrophy with inactivity compared with other muscles. Thus, identifying an effective training modality for the triceps surae is warranted. This study compared triceps surae muscle hypertrophy after standing/knee-extended versus seated/knee-flexed plantarflexion (calf-raise) training, where the gastrocnemius is lengthened and shortened, respectively. Methods: Fourteen untrained adults conducted calf-raise training with one leg in a standing/knee-extended position and the other leg in a seated/knee 90°-flexed position at 70% of one-repetition maximum. Each leg performed 10 repetitions/set, 5 sets/session, 2 sessions/week for 12 weeks. Before and after the intervention, magnetic resonance imaging scans were obtained to assess muscle volume of each and the whole triceps surae. Results: Muscle volume significantly increased in all three muscles and the whole triceps surae for both legs (p ≤ 0.031), except for the gastrocnemius muscles of the seated condition leg (p = 0.147-0.508). The changes in muscle volume were significantly greater for the standing than seated condition leg in the lateral gastrocnemius (12.4% vs. 1.7%), medial gastrocnemius (9.2% vs. 0.6%), and whole triceps surae (5.6% vs. 2.1%) (p ≤ 0.011), but similar between legs in the soleus (2.1% vs. 2.9%, p = 0.410). Conclusion: Standing calf-raise was by far more effective, therefore recommended, than seated calf-raise for inducing muscle hypertrophy of the gastrocnemius and consequently the whole triceps surae. This result and similar between-condition hypertrophy in the soleus collectively suggest that training at long muscle lengths promotes muscle hypertrophy.