A STRAIN-GAUGE UNIAXIAL LOAD CELL TO EVALUATE MUSCULAR STRENGTH LEVEL IN ISOMETRIC EXERCISE

Abstract

INTRODUCTION "Muscle strength is defined as the magnitude of the torque exerted by a muscle (or muscles) in a single maximal isometric contraction of unrestricted duration" (Atha, 1981 ). Strength diagnosis (Schmidtbleicher, 1992) by means of strength and power tests is considered as a very useful procedure to identify talents or to control the evolution in the tralning or rehabilitation progress. The results of specific tests provide information about relative deficiencies and they can be used to figure out individual strength training programs. Also, maximum isometric force and the rate of force development seem to be important qualities related to the athletic performance (Wilson and Murphy, 1995). In consequence of this study a strain-gauge uniaxial load cell has been designed and developed to measure in real-time, and store the well established mechanical parameters to evaluate muscular force during isometric exercise. These parameters are: a) the peak value of the force exerted on the load b)the time to reach a predetermined percentage of its maximum value c) the gradient of the force-time curve d) the interval to maintain a determined level of isometric force. The measurement chain includes: i) the load cell which is an lnstrumentated steel ring with a Wheatstone circuit ii) the amplifier iii) a low-pass analogic filter iv) an AID converter v) the personal computer with mathematical processor and the software for signal treatment and results' representation. RESULTS An INSTRON electro-hydraulic testing system has been used to calibrate the measurement chain and to evaluate its performance (r = -.999, pc ,00000). The measurement range of the load cell is up to 3500 N, its precision is k5 N and its sampling rate is 500 Hz. The software permits the representation of the results in real-time providing the possibility for feedback applications. CONCLUSION Convenient technical characteristics recommend the use of this uniaxial load cell to evaluate muscle strength capacity in isometric conditions.. REFERENCES Atha, J. (t981). Strengthening muscle. In D.I. Miller (Ed.) Exercise and Sport Science Reviews, vol. 9, 1-73. Philadelphia Franklin Institute. Shmidtbleicher, D. (1 992). Training for Power events, Strength and Power in Sport. P.V. Komi (Ed.), 381-395, Blackwell. Wilson, G. J.; Murphy A.J. (1 995). Strength Diagnosis: the use of the pre-training test data to determine individual specific strength training. XVth I.S.B. Congress. Book of abstracts, 994-995.