Reliability in One-Repetition Maximum Performance in People with Parkinson's Disease

Strength training is an effective modality to improve muscular strength and functional performance in people with Parkinson's disease (PWP). One-repetition maximum (1-RM) is the gold standard assessment of strength; however, PWP suffer from day-to-day variations in symptom severity and performance characteristics, potentially adversely affecting the reliability of 1-RM performance. Herein, we assessed the reliability of 1-RM in PWP. Forty-six participants completed two sessions of 1-RM testing of knee extension, knee flexion, chest press, and biceps curl at least 72 hours apart. Significantly differences between testing sessions were identified for knee extension ( < 0.001), knee flexion ( = 0.042), and biceps curl ( = 0.001); however, high reliability (ICC > 0.90) was also identified between sessions. Interestingly, almost third of subjects failed to perform better on the second testing session. These findings suggest that 1-RM testing can be safely performed in PWP and that disease-related daily variability may influence 1-RM performance. 1. Introduction Parkinson’s disease (PD), a progressive neurological disease which is believed to affect over 1.5 million Americans, results from the degeneration of the dopaminergic neurons in the midbrain and the resulting reduced dopamine availability to the basal ganglia [1, 2]. The cardinal features of PD include rigidity, tremor, bradykinesia, and impaired postural control, and these symptoms are often unpredictable and their severity can fluctuate daily, often termed “day-to-day variability” [3–5]. Further, muscular weakness, identified by Dr. Parkinson as an early symptom of the disease, is also frequently reported by people with Parkinson’s (PWP) [6, 7]. However, inconsistent findings in the literature have obscured the elucidation of the underlying mechanism of the apparent weakness, thus, raising the debate if muscular weakness is intrinsic to the disease or a secondary consequence [8, 9]. Muscular weakness, when present in PWP, presents bilaterally and tends to increase as the velocity of movement increases [9]. While the specific contributory neurophysiological mechanisms remain uncertain, bradykinesia, the inability to energize the appropriate muscles to generate forces at a sufficient rate, is thought to be a major contributing factor [8, 10]. Bradykinesia likely results from basal ganglia pathophysiology leading to impairments in both motor programming and execution [11]. Muscular weakness and bradykinesia impair power production, particularly at lighter loads [8]. These reductions in muscular