This cross-sectional study compares isometric lower limb muscle strength and contractile properties measured by tensiomyography (TMG) in 60 older adults aged 58–85 years (20 with Parkinson's disease and 40 healthy controls; 39 men, 21 women). Patients with Parkinson's disease showed an increased contraction time (Tc, between 10 and 90% of maximal contraction) by +23.6% and decreased maximal muscle displacement (Dm) in the lateral gastrocnemius compared to healthy controls. Sarcopenic participants had lower maximal isometric strength in hip extension by -29.5% and in knee extension by -26.2% based on maximal voluntary contraction. Muscle strength was assessed during eight main movements of the lower limbs using a hand-held dynamometer, and the contractile properties of four muscles: lateral gastrocnemius, medial gastrocnemius, soleus and tibialis anterior. Parkinson's disease is a progressive neurodegenerative disorder with motor symptoms such as bradykinesia and rigidity, while sarcopenia is an age-related condition with loss of muscle mass and strength. Both conditions impair mobility and increase the risk of falls, but their physiological features differ. Results suggest different neuromuscular patterns in Parkinson's disease and sarcopenia.