Using submaximal contractions to predict the maximum force‐generating ability of muscles

Abstract

Introduction Muscle weakness can be caused by decreases in either the maximum force generating ability of a muscle (MFGA) or neural drive from the nervous system (e.g., following a stroke). Presently, there is no agreed upon practical method for calculating the MFGA in individuals with central nervous system pathology. The purpose of this study was to identify the best method of determining the MFGA. Methods The predicted and estimated MFGA of the muscles of 23 non-neurologically impaired subjects (13M, 21.9 +/- 1.9 years) were compared using the burst superimposition, twitch interpolation, doublet interpolation, twitch-to-tetanus ratio, and adjusted burst superimposition methods. Results The adjusted burst superimposition test was the most accurate predictor of MFGA. Discussion Further testing is needed to validate the use of the adjusted burst superimposition test in a neurologically impaired population.

Comparison of techniques to determine human skeletal muscle voluntary activation

“…These burst stimulation characteristics have been used in different clinical studies [Farquhar et al, 2005; Flynn et al, 2012; Stackhouse et al, 2000, 2003] and elicit a maximal force response from quadriceps [Stackhouse et al, 2003]. If required, subjects were given a maximum of three trials- separated by 5 min rest- to reach a VAR CAR ≥ 95%.…”

“…When the muscle weakness is of central origin, it is defined as volitional activation (VA) failure and indicates either incomplete motor unit recruitment or suboptimal discharge rates of those units [Gandevia, 2001]. VA failure has been reported in older adults and in individuals with knee pathologies or neurological disorders [Farquhar et al, 2005; Flynn et al, 2012; Stackhouse et al 2003]. The identification of the VA failure may assist in developing effective rehabilitation protocols that include electrical stimulation or biofeedback to maximize strength gains in these populations.…”

“…Additionally, Krishnan & Williams [2010] found that when the maximum volitional force was used as a reference (regardless when it occurred) for calculating VA, the CAR technique yielded inaccurate VA findings. Therefore, a curvilinear equation [Stackhouse et al, 2000, 2003], a correction factor [Flynn et al, 2012] and using the voluntary force just prior to stimulus as the reference force for calculating VA [Krishna & Williams, 2010] have been recommended to correct the VA ratio value.…”

“…Past studies have compared the ability of both activation techniques to detect VA failure [Bampouras et al, 2006; Behm et al, 2001; Flynn et al, 2012; Grindstaff & Threlkeld, 2014; Krishna & Williams, 2010] concluding that the CAR provides artificially higher VA ratios than the IT because the CAR calculation precludes normalization of the superimposed force to the resting electrically induced force [Krishna & Williams, 2010]. In contrast, the burst and adjusted burst CARs (a correction equation is used to adjust for the associated CAR error) estimated more accurately VA compared to the IT (twitch and doublet stimulus) during submaximal isometric contractions of the plantarflexor muscles [Flynn et al, 2012].…”

“…In contrast, the burst and adjusted burst CARs (a correction equation is used to adjust for the associated CAR error) estimated more accurately VA compared to the IT (twitch and doublet stimulus) during submaximal isometric contractions of the plantarflexor muscles [Flynn et al, 2012]. Consideration should also be given to the force that is used as a reference for VA computations, since such detailed methodological information is usually omitted, and it might be a contributing factor in the variability of the VA reported values [Miller et al, 2006].…”