The optimal stimulation pattern for skeletal muscle is dependent on muscle length

Abstract

Abstract-Stimulation patterns can be optimized by maximizing the force-time integral (FTI) per stimulation pulse of the elicited muscle contraction. Such patterns, providing the desired force output with the minimum number of pulses, may reduce muscle fatigue, which has been shown to correlate to the number of pulses delivered. Applications of electrical stimulation to use muscle as a controllable biological actuator may, therefore, be improved. Although muscle operates over a range of lengths, optimized patterns have been determined only at optimal muscle length. In this study, the patterns with up to four pulses that produced the highest isometric FTI were determined at 10 muscle lengths for 11 rabbit tibialis anterior muscles. The interpulse intervals (IPIs) used ranged from 4 to 54 ms. At high muscle length, the optimal stimulation pattern consisted of an initial short IPI (doublet) followed by longer IPIs, in agreement with previous studies. However, at low length, the third pulse still elicited more than linear summation (triplet); furthermore, the relative enhancement of the FTI per pulse was considerably larger at low length than at high length, suggesting that optimal stimulation patterns are length dependent.

Catchlike property of skeletal muscle: Recent findings and clinical implications

“…53 Muscle Length. Catchlike-inducing trains produced greater force augmentation at short rather than longer muscle lengths, in both fatigued and nonfatigued human quadriceps femoris, 55 mouse flexor digitorum brevis, 1 rabbit tibialis anterior, 61 and cat soleus muscles. 71 The diminished force augmentation at longer muscle lengths has been ascribed to the decreased cross-bridge sensitivity to Ca 2ϩ at muscle lengths shorter than optimal.…”

“…24,33,35 Consistent with this mechanism of increased Ca 2ϩ release is the observation that force augmentation due to the catchlike property is more pronounced in stimulation conditions when the excitation-contraction coupling process is compromised, 3,33,71 such as during low-frequency fatigue 11,20 and at short muscle lengths. 1,55,61 Considerable evidence supports increased stiffness of the visco-elastic elements of muscle as a factor causing force augmentation due to the catchlike property. Parmiggiani and Stein compared a skeletal muscle to an elastic band, and gave the analogy of improved transmission of force in a taut band compared to a slack one.…”

Effects of series elastic compliance on muscle force summation and the rate of force rise

“…The activation dynamics of muscle, especially the kinetics of sarcoplasmic Ca 2+ release and reuptake (Duchateau and Hainaut, 1986b;Barclay, 2012), are likely important determinants of force generation in response to consecutive stimuli. Indeed, doublet force summation is influenced by factors that alter the Ca 2+ sensitivity of the contractile apparatus Williams, 1982, 1985;Sweeney and Stull, 1990), including muscle length (Wallinga-de Jonge et al, 1980;Mela et al, 2002), muscle temperature (Ranatunga, 1977) and post-activation potentiation (Baudry et al, 2005). These same factors have been shown to also influence the twitch:tetanus ratio (Ranatunga, 1977;Stein and Parmiggiani, 1981;Moore and Stull, 1984), which appears to be inversely related to doublet force summation (Duchateau and Hainaut, 1986a).…”

Automated rodent in situ muscle contraction assay and myofiber organization analysis in sarcopenia animal models

“…On the other hand, several hurdles limited broader application of the protocol to routine in vivo efficacy studies, including slower workflow of the animal surgery procedures, assay system set-up, and muscle elongation during contraction. The plantarflexor muscle group elongates significantly during the first few contractions, which can compromise force output and therefore, compromise accuracy of force measurements (38,45). We developed an in situ assay system, which incorporated automated DAQ, data analysis, and used curve fitting to collect the data for several parameters that characterize the contractile properties of myofiber subtype populations.…”