Table 4.

Normalized electromyography (EMG).

Firm	MG (%)	LG (%)	SOL (%)	TA (%)	Coactivation ratio (%)
Bipedal PD	20.5 ± 10.4	36.7 ± 25.9#	25.2 ± 10.9	23.1 ± 22.7#	32.1 ± 36.8
Bipedal OA	18.7 ± 16.4	16.4 ± 7.5	21.7 ± 21.3	10.3 ± 9.9	30.1 ± 39.2
Unipedal PD	68.4 ± 44.6*	85.0 ± 41.0*#	66.2 ± 29.8*	85.1 ± 44.9*#	63.2 ± 66.6
Unipedal OA	52.6 ± 41.0*	42.9 ± 19.1*	73.8 ± 44.6*	64.6 ± 31.3*	44.7 ± 16.1
Compliant
Bipedal PD	17.7 ± 11.4	39.9 ± 27.6#	25.5 ± 10.3	29.7 ± 27.6#	65.3 ± 66.3
Bipedal OA	16.5 ± 7.2	16.1 ± 6.3	23.4 ± 19.8	10.1 ± 6.7	18.5 ± 11.8
Unipedal PD	72.4 ± 53.8*	92.9 ± 35.3*#	73.8 ± 44.6*	106.8 ± 62.7*#	58.0 ± 59.2*
Unipedal OA	37.2 ± 18.8*	38.3 ± 14.6*	80.1 ± 58.6*	54.1 ± 22.8*	33.0 ± 18.0*

Values are root mean squared EMG normalized to their respective maximum value during plantar flexion (MG, LG, SOL) or dorsiflexion (TA) MVC and expressed as percentages. Coactivation ratio was calculated by dividing the normalized TA activation by the sum of the normalized plantar flexors EMG and multiplying by 100. PD, older adults with Parkinson’s disease; OA, healthy older adults. MG, medial gastrocnemius; LG, lateral gastrocnemius; SOL, soleus; TA, tibialis anterior. *, differs from bipedal stance for same surface condition (p < 0.001). #, differs between older adults with PD and health older adults within same stance and condition (p < 0.05).