Determining the Extent of Neural Activation during Maximal Effort

Kendall, Tracee L.; Black, Christopher D.; Elder, Christopher P.; Gorgey, Ashraf S.; Dudley, Gary A.

doi:10.1249/01.mss.0000228953.52473.ce

Cited by 29 publications

(17 citation statements)

References 21 publications

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“…Following a 3-min stimulation protocol, the proportion of muscle activated as computed using MRI images was substantially less than that computed using MVC-superimposed electrical stimulation methods (Kendall et al 2006). Although Adams et al (1993) also found considerably less than 100% of muscle Wbers activated using T 2 -weighted images following electrical stimulation, they noted "…moving both electrodes… markedly changed the pattern of stimulation of m. quadriceps femoris."…”

Section: Discussionmentioning

confidence: 92%

“…Although Adams et al (1993) also found considerably less than 100% of muscle Wbers activated using T 2 -weighted images following electrical stimulation, they noted "…moving both electrodes… markedly changed the pattern of stimulation of m. quadriceps femoris." Thus, although the MRI data suggests that maximal eVort results in the activation of only 75% of muscle Wbers (Kendall et al 2006), this might be partly attributable to the diYculty of fully activating motoneurons using electrical stimulation. Moreover, Kendall et al (2006) used an electrical stimulation protocol that elicited only 49% MVC.…”

Section: Discussionmentioning

confidence: 96%

“…Thus, although the MRI data suggests that maximal eVort results in the activation of only 75% of muscle Wbers (Kendall et al 2006), this might be partly attributable to the diYculty of fully activating motoneurons using electrical stimulation. Moreover, Kendall et al (2006) used an electrical stimulation protocol that elicited only 49% MVC. We have recently found that in another large muscle, the biceps brachii, new motor unit recruitment can occur even above 90% MVC (unpublished observations).…”

Section: Discussionmentioning

confidence: 96%

“…A recent study concluded that the interpolated twitch technique highly overestimates the number of motor units activated (Kendall et al 2006). Following a 3-min stimulation protocol, the proportion of muscle activated as computed using MRI images was substantially less than that computed using MVC-superimposed electrical stimulation methods (Kendall et al 2006).…”

Section: Discussionmentioning

confidence: 99%

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Relationships between voluntary activation and motor unit firing rate during maximal voluntary contractions in young and older adults

Knight

Kamen

2008

Eur J Appl Physiol

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The extent to which an individual can voluntarily produce maximal muscular force can be estimated using the interpolated twitch technique. Incompleteness of activation is typically attributed to either incomplete recruitment, suboptimal firing rates or both of these mechanisms. The purpose of this study was to assess the relationship between muscle activation and maximal motor unit firing rates. Measures of muscle activation and motor unit firing rates during maximal effort contractions were obtained from 15 subjects (8 young, 7 older) throughout a 6-week strength training program for the knee extensors. High resolution interpolated twitch responses were obtained using a circuit that removes the force level of the maximal voluntary contraction prior to amplification of the additional evoked force. Maximal firing rates were obtained using a four-wire needle electrode. Electrical stimulation of the knee extensors during maximal effort contractions evoked a transient increase in the force and the amplitude of this additional force was correlated with maximal firing rates at r = -0.62 (p < 0.05). Central activation ratio and activation level, two indexes of activation, were correlated with maximal firing rates at r = 0.58 (p < 0.05) and r = 0.68 (p < 0.05), respectively. The training program elicited parallel increases in muscular activation and maximal firing rates. These results provide direct support for maximal firing rate as a significant factor limiting maximal force production.

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Section: Discussionmentioning

confidence: 92%

Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Relationships between voluntary activation and motor unit firing rate during maximal voluntary contractions in young and older adults

Knight

Kamen

2008

Eur J Appl Physiol

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“…As well as differences in muscle fibre-type composition between different muscle groups (Johnson et al 1973), variations in electrical muscle stimulation protocols (more specifically the pulse duration or frequency of stimuli) used to generate a joint moment may partly explain the variability in specific tension values reported between some studies (Maganaris et al 2001;Gorgey et al 2006). In addition, voluntary muscle activation was determined using the ITT in the present study, while a combination of T2-MRI and neuromuscular stimulation has been used for the same purpose in several other investigations (Adams et al 1993;Kendall et al 2006). The latter method generally demonstrates a lower voluntary muscle activation capacity (*75%) than the ITT (*90%) and hence would lead to differences between studies when calculating muscle specific tension in vivo.…”

Section: Discussionmentioning

confidence: 98%

In vivo specific tension of the human quadriceps femoris muscle

et al. 2009

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It is not known to what extent the inter-individual variation in human muscle strength is explicable by differences in specific tension. To investigate this, a comprehensive approach was used to determine in vivo specific tension of the quadriceps femoris (QF) muscle (Method 1). Since this is a protracted technique, a simpler procedure was also developed to accurately estimate QF specific tension (Method 2). Method 1 comprised calculating patellar tendon force (F (t)) in 27 young, untrained males, by correcting maximum voluntary contraction (MVC) for antagonist co-activation, voluntary activation and moment arm length. For each component muscle, the physiological cross-sectional area (PCSA) was calculated as volume divided by fascicle length during MVC. Dividing F (t) by the sum of the four PCSAs (each multiplied by the cosine of its pennation angle during MVC) provided QF specific tension. Method 2 was a simplification of Method 1, where QF specific tension was estimated from a single anatomical CSA and vastus lateralis muscle geometry. Using Method 1, the variability in MVC (18%) and specific tension (16%) was similar. Specific tension from Method 1 (30 +/- 5 N cm(-2)) was similar to and correlated with that of Method 2 (29 +/- 5 N cm(-2); R (2) = 0.67; P < 0.05). In conclusion, most of the inter-individual variability in MVC torque remains largely unexplained. Furthermore, a simple method of estimating QF specific tension provided similar values to the comprehensive approach, thereby enabling accurate estimations of QF specific tension where time and resources are limited.

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Phenotypic plasticity and functional asymmetry in response to grip forces exerted by intercollegiate tennis players

Lucki

Nicolay

2007

American J Hum Biol

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This study examined phenotypic and functional responses to extreme asymmetry in hand use, and recorded the grip forces that occur during the tennis serve to assess the forces that contribute to asymmetry. Compressive grip performance was measured for Division I collegiate tennis players (24 female, 24 male) and nonathlete college students (18 females, 17 males) during three experiments: single-repetition maximum voluntary contraction, 30 consecutive repetitions, and a 30-s static hold. Tennis players had significant asymmetry in both forearm circumference and grip strength. The dominant hand of female tennis players produced 25% more force than the opposite hand, while the difference between hands of male tennis players was 18%. However, endurance over 30-repetitions and during the 30-s hold did not significantly differ between the limbs of tennis players. No significant asymmetry in forearm measurements, grip strength, or endurance was detected between the limbs of nonathletes. Grip forces generated during the tennis serve were recorded for 4 male tennis players, using a racket with a dynamometer incorporated into the handle. Peak handgrip forces generated during the serve (150-250 N) averaged 31-44% of the maximum grip force of the participant. Tennis players have increased muscle mass and strength of the dominant limb. Moderate forces, occurring hundreds of times each match and practice, are likely the primary forces contributing to this morphological and functional asymmetry.

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Determining the Extent of Neural Activation during Maximal Effort

Cited by 29 publications

References 21 publications

Relationships between voluntary activation and motor unit firing rate during maximal voluntary contractions in young and older adults

Relationships between voluntary activation and motor unit firing rate during maximal voluntary contractions in young and older adults

In vivo specific tension of the human quadriceps femoris muscle

Phenotypic plasticity and functional asymmetry in response to grip forces exerted by intercollegiate tennis players

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