Muscular Fatigue and Endurance During Intermittent Static Efforts: Effects of Contraction Level, Duty Cycle, and Cycle Time

Abstract

Design changes to reduce the occurrence of localized fatigue during intermittent work need to take into account all the task parameters simultaneously.

An Exploration of the Effects of Cycle Time and Force Variations on Muscle Fatigue during Submaximal Intermittent Isometric Exertions

“…RPE, a good indicator of perceptual fatigue (Iridiastadi & Nussbaum, 2006;Enoka & Duchateau, 2008), significantly increased, while maximal voluntary force production significantly decreased over time, which is also indicative of localized muscle fatigue (LMF) (Bigland-Ritchie & Woods, 1984;Garland et al, 1994;Enoka & Duchateau, 2008). The increase in EMG amplitude is often used to estimate muscle fatigue under sub-maximal isometric conditions since it infers an increased recruitment of motor units as a result of LMF (SjØgaard et al, 1986;Hermans & Spaepen, 1997;Hunter & Enoka, 2003;Chang et al, 2016).…”

“…A static, or isometric, exertion is one during which no movement occurs at the joint, while a dynamic exertion results in lengthening (eccentric exertion) or shortening (concentric exertion) of the muscle (Tortora & Derrickson, 2009). Such force exertions can either be prolonged, which means the muscular force is continuously sustained, whereas intermittent muscle exertions display variations in the activation levels, including stopping and starting at regular or irregular intervals (Iridiastadi & Nussbaum, 2006). Prolonged static exertions have been widely studied for the development of LMF (e.g., Rohmert, 1960;Gamet & Maton, 1989;Hunter & Enoka, 2003), and the relationship between the endurance time and isometric level of muscle effort is well established.…”

“…Studies by Mathiassen (1993) and Iridiastadi & Nussbaum (2006) that investigated the interactions between the three task elements of intermittent work showed the muscle fatigue was sensitive to the intermittent elements. However, these studies did not maintain the same overall workload, meaning muscle fatigue development could have been affected by the overall effort and not the intermittent characteristics (Yassierli & Nussbaum, 2007;Dickerson et al, 2015).…”

“…Within a single cycle, the duty cycle determines the duration of the muscle activation; in other words, the proportion of time an individual is engaged in the frequency of the task (Potvin, 2012). Researchers such as Iridiastadi & Nussbaum (2006), Dickerson et al (2015), and Rashedi & Nussbaum (2016) claim that shorter cycle times could be linked to a slower development of muscle fatigue as shorter cycle times tended to have "positive physiological effects", although the latent benefits of varying cycle times across a range of tasks still had to be defined (Iridiastadi & Nussbaum, 2006). Finneran & O'Sullivan (2010), on the other hand, believe that longer cycle times that include varieties of subtasks (e.g., with varying force variations and duty cycles) may be more beneficial than short cycle times, as highly repetitive tasks can lead to increased pressure on the peripheral nerves.…”

“…Iridiastadi & Nussbaum (2006) pointed out that a large portion of modern industrial tasks that require prolonged low-level repetitive work between 12-28% MVIE have led to occupational problems and complaints. Vøllestad et al (1997) also noticed that 25% of MVIE was a safe muscle activation level at which to study muscle fatigue.…”