May 2007

Evaluation of viscoelastic parameters of the skeletal muscles in junior triathletes

Georg Gavronski, Alar Veraksitš, Eero Vasar, Jaak Maaroos
Department of Sports Medicine and Rehabilitation, Department of Physiology, University of Tartu
Physiological Measurement - May 2007, Volume 28, Number 6, Page 625 (DOI: 10.1088/0967-3334/28/6/002)

Five male triathletes of the Estonian national junior team were observed during a seven-week competition period. The Myoton-2 equipment was used to describe the viscoelastic parameters of the skeletal muscles. The frequency of damped mechanical oscillation of the muscle tissue (Hz—indicating the tension in the muscle), logarithmic decrement of the oscillations (Θ—indicating the elasticity of the muscle) and stiffness (N m−1) of the muscle tissue were registered bilaterally in eight muscles in both the relaxed and the contracted states: BB—biceps brachii (caput longum); TB—triceps brachii (caput longum); BF—biceps femoris (caput longum); RF—rectus femoris; TA—tibialis anterior; GC—gastrocnemius (caput mediale); LD—latissimus dorsi; PM—pectoralis major (pars sternocostalis). A portable massage table was used for the subject to rest on during the measuring. For the measurement of the anterior muscles, the subject lay supine; for the posterior muscles the prone position was used. The (isometric) contraction was standardized simply by the same measuring position of the limb—the subject raised his arm or leg to an angle of 45° from the horizontal level, using a 2.3 kg dumb-bell as an additional weight for the upper limb. The tarsal dorsiflexion and plantarflexion was performed against a fixed table to contract the crural muscles. The elasticity of the skeletal muscle is higher for the contracted state with respect to the relaxed one (p < 0.0001) and is described by decline of the value of logarithmic decrement, the stiffness and the tension in the muscle increases (p < 0.0001 for both parameters). The measured skeletal muscles differ significantly (p < 0.0018) by the viscoelastic properties in the relaxed state. In the relaxed state, TA was the most elastic (mean ± SD; Θ—0.74 ± 0.13), stiff (mean ± SD; 346.68 ± 60.34 N m−1) and tense muscle (mean ± SD; 18.72 ± 1.55 Hz). In the contracted state, the elasticity of TA did not change (0.76 ± 0.14) while the stiffness and the tension in this muscle rose significantly (93% and 38%, accordingly). Personal differences (p < 0.005) exist if pooled data from the muscles are compared between the subjects.

The working principle of Myoton-2, measuring the mechanical oscillations of the tissue is unique and this field is unexplored. This paper supports the use of myotonometry as an objective method to evaluate the status of the skeletal muscles. All the three established parameters are important because in certain muscles these parameters may act differently. Due to the simplicity of the method and the mobility of the equipment, it can be easily used both in field and stationary conditions in sports medicine to objectively evaluate the condition of the skeletal muscles. The measured parameters are individual- and muscle-specific.