Affiliations: [a] Department of Physical Therapy, Chang Gung University, Kweishan, Taoyuan, Taiwan | [b] Graduate Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan
Correspondence:
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Address for correspondence: Yang Hua Lin, Ph.D, Department of Physical Therapy, Chang Gung University, 259, Wen-Hwa 1st Rd., Kweishan, Taoyuan, Taiwan, 333. Tel.: +886 3 3283016 5438; Fax: +886 3 3283031; E-mail: linyh@mail.cgu.edu.tw
Abstract: Objective:This investigation aims to determine whether optimal muscle length was estimated with joint toque generated by maximal voluntary isometric muscle contraction (MVIC), which differed from that was estimated with joint torques generated through electrical stimulation superimposed on MVIC (MVICES). Design:An experimental investigation was conducted to measure joint torques of the elbow joint in the conditions with MVIC and with MVICES. The measured joint torques were used to examine the level of neuromuscular activation under MVIC condition as well as to estimate the optimal muscle length of elbow flexors by using in a theoretical muscle model with various conditions of muscle contraction. Background:Usually muscle model parameters such as maximum muscle force, optimal length are estimated by the joint torques measured during MVIC, assuming maximum level of neuromuscular activation. However, several experimental studies have shown that MVIC are in fact submaximal contraction and cannot represent as complete neuromuscular activation. As a result, the use of MVIC for the estimation of muscle model parameters may not be appropriately able to produce satisfactory results. Methods:Eight subjects first performed MVIC of their elbow flexors. Electrical stimulation was superimposed to MVIC to induce true maximal contraction of the muscles. The resulting joint torques were measured in each test condition and used to calculated the optimal muscle lengths by a muscle model combined with an optimization procedure. Comparisons of the results for the two conditions were made with paired T test. Results:The joint torques produced by electrically stimulated the elbow flexors at the elbow joint were statistically higher than those produced by maximal voluntary contraction. Optimal muscle lengths estimated through the joint torques generated by MVIC with electrical stimulation were statistically different from those estimated without electrical stimulation. The optimal lengths of the elbow flexors were calculated with adjusting the neuromuscular activation to be submaximal level and showed no statistically difference from that estimated with superimposed electric stimulation. Conclusion:Joint torques used for estimating optimal muscle lengths are better derived from electrical stimulation superimposed on MVIC of the relevant muscles or MVIC accompanied with adjusting the level of neuromuscular activation in the range of 0.62 to 0.93.
