Search

The purpose of this study was to investigate changes in muscle spindle sensitivity with early and late soleus reflex responses via tendon taps and transcranial magnetic stimulation, respectively, after an acute bout of prolonged static plantar flexor muscle stretching. Seventeen healthy males were tested before and after 5 min (5 × 60-s stretches) of passive static stretching of the plantar flexor muscles. Maximal voluntary isometric torque and M wave-normalized triceps surae muscle surface electromyographic activity were recorded. Both soleus tendon reflexes, evoked by percussion of the Achilles tendon during rest and transcranial magnetic stimulation-evoked soleus late responses during submaximal isometric dorsiflexion were also quantified. Significant decreases in maximal voluntary isometric plantar flexion torque (−19.2 ± 13.6%, p =.002) and soleus electromyographic activity (−20.1 ± 11.4%, p <.001) were observed immediately after stretching, and these changes were highly correlated (r = 0.76, p <.001). No changes were observed in tendon reflex amplitude or latency or peak muscle twitch torque (p >.05). Significant reductions in soleus late response amplitudes (−46.9 ± 36.0%, p =.002) were detected, although these changes were not correlated with changes in maximal electromyographic activity, torque or tendon reflex amplitudes. No changes in soleus late response latency were detected. In conclusion, impaired neural drive was implicated in the stretch-induced force loss; however, no evidence was found that this loss was related to changes in muscle spindle sensitivity. We hypothesize that the decrease in soleus late response indicates a stretch-induced reduction in a polysynaptic postural reflex rather than spindle reflex sensitivity.

Introduction: Muscle force production is usually impaired in people with spinal cord injury (SCI). The use of high-intensity neuromuscular electrical stimulation (NMES) strength training can help promote metabolically active lean muscle mass and, thus, increase muscle mass and improve physical health and quality of life (QoL). Nonetheless, NMES is usually used at low-stimulation intensities, and there is limited evidence on the effects of high-intensity NMES strength training into improving muscle force and mass, symptoms of spasticity, or physical health and QoL in people with SCI. Methods: Five individuals with chronic SCI completed five 10-repetition sets of high-intensity knee extension NMES strength training sessions for 12 wk in both quadriceps muscles. Quadriceps femoris (QF) knee extensor torque was measured on a dynamometer, and cross-sectional area (CSAQF) was measured with extended field-of-view ultrasonography. Venous blood samples were collected for blood lipid profiling and C-reactive protein analyses. The Spinal Cord Injury Spasticity Evaluation Tool was used to assess symptoms of spasticity, and the QoL index SCI version III was used for QoL measures. Results: QF tetanic knee extensor torque increased on average by 35% (2%–92%), and CSAQF increased by 47% (14%–145%). A significant increase in the HDL/LDL cholesterol ratio (P < 0.001) and a mean significant improvement of 4.8% ± 2.3% (absolute value = 0.26) in the Spinal Cord Injury Spasticity Evaluation Tool score was observed, whereas QoL showed a near-significant improvement in the health and functioning domain (15.0 ± 4.2 and 17.3 ± 5.1; P = 0.07).

Spinal cord injury (SCI) leads to significant deficits in muscle strength and mass, impacting negatively on physical health and quality of life (QoL). Physical rehabilitation techniques for people with SCI rely on constant updates and the accumulation of evidence regarding the efficacy of available and/or new physical interventions. Neuromuscular electrical stimulation (NMES) is already commonly used to activate skeletal muscles and subsequently reverse muscle atrophy, however NMES as a high-intensity “strength training” intervention appears to be a particularly promising technique for increasing muscle strength and mass and to subsequently improve physical health and quality of life (QoL) in people with SCI. Nonetheless, there are many factors limiting the use of standard NMES protocols, and further evidence pertaining to the use of high-intensity NMES strength training in clinical populations is warranted. The primary aim of the research described in this thesis was to examine the effects of NMES as a high-intensity muscle strength training intervention, specifically using wide-pulse width (1000 μs), low-to-moderate frequency (30 Hz) NMES combined with tendon vibration, on muscle strength and mass, physical health, symptoms of spasticity and QoL in people with SCI. This thesis includes two cross-sectional studies examining the effects of patellar tendon vibration (55 Hz, 7 mm amplitude) superimposed onto wide-pulse width (1000 μs) NMES (e.g. 30 Hz over 2 s) on the peak muscular (knee extensor) force and total impulse elicited by, and rate of recovery from, the intervention in healthy subjects (Study 1) and in people with chronic SCI (Study 2). The results of Study 1 revealed that superimposing tendon vibration onto wide-pulse width NMES leads to an increase in the muscle work performed before fatigue in only some individuals (i.e. positive responders, 50% of individuals in the current study), but decreases it in others (i.e. negative responders). However, it tends

Pulverenti, T. S., Trajano, G. S., Kirk, B. J. C., Bochkezanian, V., & Blazevich, A. J. (2021). Plantar flexor muscle stretching depresses the soleus late response but not tendon tap reflexes. European Journal of Neuroscience, 53(9), 3185-3198. https://doi.org/10.1111/ejn.15178

Bochkezanian, V., Newton, R. U., Trajano, G. S., Vieira, A., Pulverenti, T. S., & Blazevich, A. J. (2017). Effect of tendon vibration during wide-pulse neuromuscular electrical stimulation (NMES) on the decline and recovery of muscle force. BMC neurology, 17(1), 82. Available here

Bochkezanian, V., Newton, R. U., Trajano, G. S., Vieira, A., Pulverenti, T. S., & Blazevich, A. J. (2018). Effect of tendon vibration during wide-pulse neuromuscular electrical stimulation (NMES) on muscle force production in people with spinal cord injury (SCI). BMC Neurology, 18(1), 17. doi:10.1186/s12883-018-1020-9 Available here.

This is an Author's Accepted Manuscript of: Bochkezanian, V., Newton, R. U., Trajano, G. S., & Blazevich, A. J. (2018). Effects of Neuromuscular Electrical Stimulation in People with Spinal Cord Injury. Medicine and science in sports and exercise, 50(9), 1733-1739. Available here.