Doublet stimulation protocol to minimize musculoskeletal stress during paralyzed quadriceps muscle testing

Abstract

With long-term electrical stimulation training, paralyzed muscle can serve as an effective load delivery agent for the skeletal system. Muscle adaptations to training, however, will almost certainly outstrip bone adaptations, exposing participants in training protocols to an elevated risk for fracture. Assessing the physiological properties of the chronically paralyzed quadriceps may transmit unacceptably high shear forces to the osteoporotic distal femur. We devised a two-pulse doublet strategy to measure quadriceps physiological properties while minimizing the peak muscle force. The purposes of the study were 1) to determine the repeatability of the doublet stimulation protocol, and 2) to compare this protocol among individuals with and without spinal cord injury (SCI). Eight individuals with SCI and four individuals without SCI underwent testing. The doublet force-frequency relationship shifted to the left after SCI, likely reflecting enhancements in the twitch-to-tetanus ratio known to exist in paralyzed muscle. Posttetanic potentiation occurred to a greater degree in subjects with SCI (20%) than in non-SCI subjects (7%). Potentiation of contractile rate occurred in both subject groups (14% and 23% for SCI and non-SCI, respectively). Normalized contractile speed (rate of force rise, rate of force fall) reflected well-known adaptations of paralyzed muscle toward a fast fatigable muscle. The doublet stimulation strategy provided repeatable and sensitive measurements of muscle force and speed properties that revealed meaningful differences between subjects with and without SCI. Doublet stimulation may offer a unique way to test muscle physiological parameters of the quadriceps in subjects with uncertain musculoskeletal integrity.

Repetitive eccentric muscle contractions increase torque unsteadiness in the human triceps brachii

“…This question is important because others used low and high frequency stimulation to characterize LFF [Rijkelijkhuizen et al, 2003; de Ruiter et al, 2005; Dundon et al, 2008; Baptista et al, 2009]. However, we have previously shown that in individuals with spinal cord injury, the doublet pulse activation is sensitive to muscle physiological properties [Dudley-Javoroski et al, 2008] and, under isometric conditions, when LFF is expected to be less, the D/S ratio increased only 8–10% [Iguchi et al, 2008], while in this study it increased over 20%. Thus, the D/S ratio appears to scale in accordance to the level of LFF induced.…”

Prior heat stress effects fatigue recovery of the elbow flexor muscles

“…Individuals with paralysis have a limited capacity to generate repetitive muscle force after SCI 57–61. Moreover, individuals with SCI lose the ability to sweat and shiver, which causes rapid shifts in core body temperature based on the environment 2.…”

Factors explaining chronic knee extensor strength deficits after ACL reconstruction

“…Speed properties of the quadriceps muscle (rate of torque rise and fall) were assessed to determine if there were chronic peripheral adaptations in the quadriceps muscle associated with its metabolic and enzymatic function using the potentiated evoked torque at rest 15. The rate of torque rise and rate of torque fall were divided by the peak evoked torque at rest to obtain normalized rates in ms −1 .…”