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 (Theta - 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 degrees 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; Theta-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.