A Head-to-Head Comparison of an Isometric and a Concentric Fatigability Protocol and the Association With Fatigue and Walking in Persons With Multiple Sclerosis

Abstract

Background. Fatigue is one of the most frequent symptoms in persons with multiple sclerosis (MS). Distinction is made between subjective perceptions of fatigue and objective measures of fatigability. Fatigability can be measured by different protocols. Yet no studies have compared isometric and concentric contraction protocols of the lower extremities head-to-head. Therefore, the purpose of the present study was to (1) compare 2 such protocols head-to-head and (2) to investigate the association between fatigability evoked by the 2 protocols and measures of fatigue and walking. Methods. A total of 45 patients with MS had their walking capacity measured objectively by the 6-minute walk test (6MWT) and subjectively by the 12-item Multiple Sclerosis Walking Scale (MSWS-12). Fatigue was measured by the Modified Fatigue Impact Scale (MFIS) and fatigability by 2 knee extension protocols: sustained isometric and concentric. Results. The sustained isometric protocol induced a higher degree of fatigability than the concentric protocol ( P < .01). Regression analyses revealed that sustained isometric fatigability was not associated with either measures of fatigue or walking (all r2 = 0.00; P = .85-.99), whereas the concentric protocol was significantly associated with fatigue ( r2 = 0.20; P < .01), 6MWT ( r2 = 0.09; P < .05), and MSWS-12 ( r2 = 0.16; P < .01). Furthermore, after adjusting for maximal strength and sex, concentric fatigability remained a strong and significant predictor of fatigue (β = 0.49) and walking (6MWT: β = −0.26; MSWS: β = 0.37). Conclusion. This study provides the first evidence that a lower-extremity concentric fatigability protocol provides superior reflection of both fatigue and walking when compared with a sustained isometric protocol. We suggest that concentric protocols should be the focus of future studies investigating fatigability.

Comparison Between Isometric and Concentric Motor Fatigability in Persons With Multiple Sclerosis and Healthy Controls – exploring central and peripheral contributions of motor fatigability

“…In HCs, the variance of the sustained isometric fatigability was mainly attributed to peripheral fatigability, whereas concentric fatigability was mainly attributed to central fatigability. The present study is a continuation of the study by Taul-Madsen et al 19 and adds a neuromuscular dimension to the observed associations of motor fatigability and clinical outcomes of the study. Taul-Madsen et al 19 reported a stronger association between the torque reduction in the concentric versus the sustained isometric protocol and pwMS perceptions of fatigue impact as well as measures of walking capacity.…”

“…This is an exploratory cross-sectional study focusing on the central and peripheral contributions of knee extensor motor fatigability from 2 different protocols (concentric vs sustained isometric) in pwMS and HCs. For further information on the study design see Taul-Madsen et al 19 A subset of pwMS (n = 31) from the published "original" study (n = 45) underwent neuromuscular examinations (ie, ITT) before and immediately after the 2 fatigability protocols. Moreover, HCs were included in the present study (n = 15) with an intended pwMS to HCs ratio of 2 to 1, matched by age (±5 years) and gender.…”

“…Both fatigability protocols were carried out using an isokinetic dynamometer (Humac Norm, CSMi, Stoughton, MA), in which pwMS and HCs were seated to perform knee extension, as described previously. 19 All participants completed a standardized warm-up prior to each of the 2 fatigability protocols. The warm-up prior to the isometric fatigability protocol consisted of 1 repetition (5-s isometric contraction) at 20%, 40%, 60%, 80%, and 100% of maximal muscle strength exertion (maximal voluntary contraction [MVC]), respectively.…”

“…These findings could perhaps be part of the explanation as to why motor fatigability from the exact concentric fatigability protocol shows a stronger association to perceptions of fatigue and to measures of walking capacity than motor fatigability from the sustained isometric protocol. 19 Furthermore, the results could guide MS rehabilitation strategies to target both central and peripheral adaptations and not aim to emphasize one or another component of the neuromuscular system.…”

“…18 However, no studies have compared the central and peripheral contributions of motor fatigability in pwMS using different protocols (eg, sustained isometric vs concentric muscle contractions). As the ITT was also applied before and after the sustained isometric and concentric fatigability protocols in a subset of participants in a recent study from our group, 19 further insight into the contributors of motor fatigability can be gained.…”