Power vs strength training to improve muscular strength, power, balance and functional movement in individuals diagnosed with Parkinson's disease

Highlights

• Strength and power training induce similar adaptations in older persons with PD.

• Similar responses allow greater flexibility during training prescriptions.

• Strength and power transfers to daily activities may require movement-specific training.

• Strength and power training appear equally tolerable in persons with PD.

Abstract

Background

Declines in strength and power are cardinal symptoms of Parkinson's disease (PD), a progressive neuromuscular disorder. Progressive resistance training (PRT) has been shown to reduce a wide variety of PD-related motor deficits; however, no study has examined differences between the two most common RT methodologies utilized in this population, high-load, low velocity strength training (ST) and low-load, high-velocity power training (PT). The primary purpose of this study was to compare the effects of ST and PT on measures of strength, power, balance and functional movement in persons with PD.

Method

Thirty-five persons with mild to moderate PD (Hoehm and Yahr Stages = 1–3; UPDRS Part III = 30.6 ± 14.0) were randomized into either a ST or PT group involving 12 weeks of supervised PRT (2 visits per week). Leg press (LP) and chest press (CP) muscular strength (1RM) and muscular peak power (PP) were assessed before and after the twelve week training period as primary outcome measures. In addition, secondary measures of balance (Berg Balance Assessment (BBA), dynamic posturography (DMA), Modified Falls Efficacy Scale (MFES)), functional movement (timed up-and-go), and quality of life (PDQ-39 summary index and Mobility subscore) were obtained at the same time points, given the impact of PD symptoms on fall probability and independence.

Results

Repeated measures ANCOVA revealed significant improvements in LP 1RM (M_diff = 54.89 kg, 95% CI: 43.38, 66.40; p < .05; d = 3.38) and CP 1RM (M_diff = 7.33 kg, 95% CI: 4.75, 9.91; p < .05; d = 2.02). Additionally, significant improvements were seen in LP_PP (M_diff = 112.27 W, 95% CI: 56.03, 168.51; p < .05; d = 1.42) and CP_PP (M_diff = 52.1 W, 95% CI: 23.38, 80.86; p = .001; d = 1.29). No significant improvements were seen for any secondary outcome measures, however BBA scores were shown to significantly decrease following the intervention (M_diff = −1.686, 95% CI: −2.89, −0.482; p = .007 d = −0.96), although this change did not reach clinical significance (clinically meaningful change = ±4.0). In addition, the ST group demonstrated significantly poorer PDQ-39_SI scores (M_diff = 4.96, 95% CI: 0.54, 9.38; p = .029), whereas the entire sample showed significantly poorer PDQ-39_MOB scores (M_diff = 4.80, 95% CI: 0.17, 9.43; p = .043; d = 0.71).

Conclusions

Both ST and PT appear to be effective at reducing the neuromuscular deficits associated with PD; however, the use of these interventions for improving functional performance was not supported.

Introduction

Age is the main risk factor associated with Parkinson's disease (PD) (de Lau and Breteler, 2006), as Lewy body pathology (Kempster et al., 2010) and declines in nigrostriatal function progress with aging (Critchley, 1931). Loss of motor function is a hallmark symptom of PD. Deficits typically manifest as bradykinesia, tremors, postural instability and rigidity, all of which impede the execution of voluntary movements (Falvo et al., 2008; Allen et al., 2010; Winogrodzka et al., 2005). As the capacity to produce and control movement deteriorates, persons with PD have been shown to adopt a more sedentary lifestyle (van Nimwegen et al., 2011), which increases their risk of adverse events and makes the maintenance of independence more difficult (Speelman et al., 2011).

Central mechanisms such as decreased neural drive and an increased sense of effort have been suggested as factors related to PD movement abnormalities, with authors postulating that motor areas are not entirely activated during movement initiation (Falvo et al., 2008). Progressive resistance training (PRT) has been shown to favorably alter muscle morphology, increase motor neuron output and firing rates, and modify motor unit synchronization through the downregulation of inhibitory pathways (Aagaard, 2003). Increases in these factors may induce peripheral and central adaptations, leading to increased strength and functional capacity in those with PD; however, strength training typically targets the force-generating capacity of individual muscle groups, ignoring velocity of movement.

Although it is well established that strength training can improve muscular strength measures in older populations, many authors have noted that these benefits may not translate into improvements in functional performance (Hazell et al., 2007; Latham et al., 2004; Bottaro et al., 2007). Importantly, decreases in movement velocity have been found to disproportionately affect PD-related deficits in neuromuscular power at light to moderate loads, whereas this decrement is not observed at heavier loads (Allen et al., 2009). Therefore, lower body power may be more essential for activities of daily living (ADL) such as walking, changing direction, and climbing stairs (Hazell et al., 2007), when compared to muscular strength in this population. Traditional strength training (ST) typically targets the force-generating capacity of a particular muscle group though high loads and slower movement speeds, whereas power training (PT) specifically targets the speed component of a muscle group through light to moderate loading patterns performed at higher speeds, shifting the load at which peak power is produced to the velocity end of the load-velocity curve (Ni and Signorile, 2017). Subsequently, PRT programs designed to improve movement initiation, speed, and neuromuscular power, as opposed to strength alone, should be considered particularly important to PD patients. To our knowledge, however, only two studies have examined the impact of PT on muscular strength, power, mobility and balance in persons with PD (Ni et al., 2016a, Ni et al., 2016b; Paul et al., 2014).

Although both ST (Schilling et al., 2010; Hass et al., 2012; Lima et al., 2013) and PT (Ni et al., 2016a, Ni et al., 2016b; Paul et al., 2014) provide valuable non-pharmacological approaches to reducing PD-related neuromuscular deficits, general recommendations for the use of one modality over the other have yet to be determined. Therefore, the primary purpose of this study was to compare the effects of PT and ST on measures of strength, power, balance and functional mobility in individuals diagnosed with PD. We hypothesized that subjects in the PT group would experience greater power increases and functional improvement than subjects in the ST group; while ST would produce greater strength gains.