THE INFLUENCE OF STATIC STRETCHING ON THE VISC0ELASTIC PROPERTIES OF M. TRICEPS SURAE
AbstractThough the practice of stretching is widely used in sports, general fitness and physiotherapy, there is still a lack of basic research in this area. This study describes the viscoelastic properties of m. triceps surae and investigates the influence of static stretching. 20 males and 11 females, without a history of ankle injury, participated in this experiment. Each testee completed two sessions of seven measurements on an active omnikinetic dynamometer (PROMETT-system). The velocity of the leverarm has been kept constant during all tests (lO°/s). An interactive loop determines the stretching amplitude depending on the force exerted on this lever. The subject was fixated in an adjustable chair, the right leg extended and sustained, the left leg maximally bended in the hip to stabilize the pelvis. Further on, wooden plates were placed between the back of the chair and the pelvis to avoid any hip displacements while exerting force on the foot. After aligning the ankle axis with the axis of the dynamometer, the leverarm was manipulated to determine the moment (Mcrit) and the angle associated with a stretch just short of causing pain. The first and last measurement,of each session was an isokinetic stretch up to Mcrit (Stretch). After a short hold (200 me) in this extreme position (Hold) the same isokinetic movement, but in opposite direction, was used to relax the muscle (Relax). Between-these two 'control measurements' five identic static stretches were performed. These stretches were varied among subgroups regarding the intensity of the Stretch (90% or 100% of Mcrit) and the duration of the Hold (10s or 30 a). Netto joint moments were calculated and expressed relatively as a function of the stretching amplitude. Eighty parameters were selected in order to describe the strain-stretch curves during Stretch and Relax phases and the stress-time curves during the Hold phases. Results obtained by comparing those parameters from first and last control measurements reveal a very stable intra-individual viscoelastic behaviour of the muscle. Though, significant differences in stretching amplitude, creep and parameters describing the shape of the relax curves were observed. Differences between subgroups show a stronger influence of the intensity to the result of the static stretch compared to the influence of a longer Hold phase. In this study females had a significant smaller stretching amplitude then males. They also had less advantages of static stretching.