A 3-D KINEMATIC STUDY OF TWO POPULAR FLEXIBILITY TESTS

Abstract

INTRODUCTION. Flexibility is the intrinsic property of body tissues which determines the range of motion achievable without injury in a Joint or group of joints Goniometers are often used to measure the range of motion of the joints. These devices have been criticized and their reliability questioned.. Part of the problem is with the instruments and part with the procedure for using them. To deeply understand the phenomenon of flexibility more accurate, precise, multiaxial measurements are desirable By using an automatic motion analyzer (accuracy 1/3000 the field of view), it was the purpose of this study to perform a 3-D analysis of two popular flexibility tests When possible, the data were compared with those obtained by standard goniometers. METHODS Four recreational athletes (age range: 24-40 yr.) were the subjects of this study They were required to perform the sit and reach test and the passive single-straight-leg raising test. Both the tests are usually used as a test for hamstring tightness even if the sit and reach test combines back and hamstring flexibility Before the measurements the subjects warm-up by performing 10 minutes of slow jogging, and slow stretching movements Ten trials for each exercise were executed with one-minute rest period between trials. Kinematic data were recorded by means of an optoelectronic system (ELITE) with a sampling rate of 100 Hz. Markers were placed on: C7, T3, T6, T9, T12, L3, and S1 to mark the spine; sacroiliac spines, iliac crests, great trochanters, femoral condiles, malleola, and fifth metatarsal heads to mark the pelvis and the lower limbs; acromions, elbows and wrists to mark the arms. The position of the internaI joint centers of the hip, knee and ankle were estimated from the position of external landmarks using a special software which inputs were anthropometric and kinematic data. The back profile was modelled using a cubic spline. RESULTS. Mean and standard deviation values of the hip range of motion during the sit and reach and the straight-leg raising test are outlined in table 1 and 2, respectively. The results showed significant bilateral differences for most of the parameters examined suggesting that evaluative procedures requiring controlateral comparisons may be inaccurate. The dynamic examination of the sit and reach exercise revealed large intersubjects differences in the way to come to the full extended position evidentiating a different degree of spine mobility among the subjects The comparison with standard goniometer measurements showed differences up to 24 degrees in the hip range of motion CONCLUSION. In summary, the model presented in this work: gives a good representation of the subjects during all the phases of the flexibility tests; provides a direct quantification of the range of motion in degrees; allows the measurement of several joints and joint actions, the control of compensatory movements, and a permanent record of the trials.