Muscle Fatigue Does Not Change the Effects on Lower Limbs Strength Caused by Aging and Parkinson's Disease

The aim of this study was to determine the impact of aging and Parkinson's disease (PD) on lower limb muscle strength before and after muscle fatigue. One hundred thirty-five individuals were distributed over seven groups according to their age (20, 30, 40, 50, 60, 70 years old) and disease. Participants performed maximum voluntary isometric contractions (MVIC) in a leg press device followed by the muscle fatigue protocol (repeated sit-to-stand task). Immediately after muscle fatigue (less than 2 min), the MVIC were repeated. The peak force, peak rate of force development (first 50, 100, 200 ms), and root mean square and peak values of the vastus lateralis and vastus medialis muscle activity during MVIC were calculated before and after muscle fatigue. We found more pronounced reductions in lower limb muscle strength parameters (lower limb force, RFD-100 and RFD-200 - p<0.05) in individuals over 50 years of age and with PD. In addition, there was an inverse relation between aging and lower limb muscle strength parameters. The main findings were the lack of changes in peak force, RFDs and muscle activity of the vastus lateralis and vastus medialis after muscle fatigue according to aging and PD, and similar lower limb muscle strength parameters (before and after muscle fatigue) and effect of muscle fatigue in PD compared to the aged groups (60 and 70 years old groups).