TY - JOUR AU - Rácz, Levente AU - Béres, Sándor AU - Hortobágyi, Tibor AU - Tihanyi, József TI - Contraction history affects the in vivo quadriceps torque-velocity relationship in humans JF - EUROPEAN JOURNAL OF APPLIED PHYSIOLOGY J2 - EUR J APPL PHYSIOL VL - 87 PY - 2002 IS - 4-5 SP - 393 EP - 402 PG - 10 SN - 1439-6319 DO - 10.1007/s00421-002-0633-1 UR - https://m2.mtmt.hu/api/publication/1306618 ID - 1306618 N1 - http://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=SPHS-876871&site=ehost-live Megjegyzés-20898482 PubMed ID: 12172879 UR: http://www.scopus.com/inward/record.url?eid=2-s2.0-0036944380&partnerID=40&md5=e7e880ec829b2521d4879c83cc1e3ea9 AB - We hypothesized that the history of contraction would affect the in vivo quadriceps torque-velocity relationship. We examined the quadriceps torque-velocity relationship of the human knee extensors at the descending and ascending limb of the torque-position relationship by initiating the knee extension at a knee angle position of 1.39 rad (80°) or 0.87 rad (50°) over a 0.52 rad (30°) range of motion under conditions of constant or linearly increasing velocity. Maximal voluntary isometric knee extension torque (M₀) was measured at 1.87 rad, 0.87 rad, and 0.35 rad, and concentric torque was measured. The subjects carried out ten maximal knee extensions at ten distinct velocities, each velocity ranging between 0.52 rad·s^-1 to 5.24 rad·s^-1 in steps of 0.52 rad·s^-1. Peak concentric torque was measured and mean torque calculated from the respective torque-time curves. Peak or mean torque, computed from the individual torque-time curves, and velocity data were fitted to the Hill equation under the four experimental conditions and the curve parameters computed. The M₀ was similar at 0.87 rad and 1.39 rad, but it was significantly lower at 0.35 rad. In the low-velocity domain of the torque-velocity curve where a plateau normally occurs, peak torque was always lower than M₀. Peak and mean torque were significantly greater under linearly increasing velocity conditions and the 1.39 rad starting knee position. Mean torque but not peak torque data could be well fitted to the Hill equation and the two computations resulted in significantly different Hill curve parameters including the concavity ratio, peak power, and maximal angular velocity. We concluded that the history of contraction significantly modifies the in vivo torque-velocity relationship of the human quadriceps muscle. Muscle mechanics and not neural factors may have accounted for the inconsistencies in the human torque-velocity relationships reported previously. LA - English DB - MTMT ER - TY - JOUR AU - Bosco, C AU - Belli, A AU - Astrua, M AU - Tihanyi, József AU - Pozzo, R AU - Kellis, S AU - Tsarpela, O AU - Foti, C AU - Manno, R AU - Tranquilli, C TI - A dynamometer for evaluation of dynamic muscle work JF - EUROPEAN JOURNAL OF APPLIED PHYSIOLOGY AND OCCUPATIONAL PHYSIOLOGY J2 - EUR J APPL PHYSIOL O VL - 70 PY - 1995 IS - 5 SP - 379 EP - 386 PG - 8 SN - 0301-5548 DO - 10.1007/BF00618487 UR - https://m2.mtmt.hu/api/publication/1306630 ID - 1306630 N1 - http://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=SPH377886&site=ehost-live AB - The validation of a new dynamometer for evaluation of dynamic muscle work is presented. The device was based on a precise measurement of load displacements of any machine using gravitational loads as external resistance. It allowed, through a sensor consisting of an infrared photo interrupter, the calculation of velocity, force and power during concentric, eccentric and stretch-shortening cycle activity. To validate the dynamometer 33 male and female track and field athletes (12 throwers and 21 jumpers) participated in the study. The throwers (4 women and 8 men) were asked to perform half-squat exercises on a slide machine with a load of 100% of the subject's body mass. The day-to-day reproducibility of half-squat exercises gave a correlation coefficient of r = 0.88, 0.97 and 0.95 for average push-off force (AF), average push-off velocity (AV), and average push-off power (AP) respectively. Comparison of half-squat measurements was performed against jumping and running test evaluation by the jumpers (7 women and 14 men). The interrelationships among the different variables studied demonstrated a strong correlation between AF, AV and AP and sprinting and jumping parameters (r = 0.53-0.97; P < 0.05-0.001). Using values of AF, AV and AP developed in half-squat exercises executed with different loads, ranging from 35% to 210% of the subject's body mass, it was also possible to establish the force-velocity and power-velocity relationships for both male and female jumpers. In any individual case, the maximal error due to the measurement system was calculated to be less than 0.3%, 0.9% and 1.2% for AF, AV, and AP respectively. Given the accuracy of the ergometer, the high reliability found between 2 days of measurements, and the specificity of the results it is suggested that the dynamic dynamometer would be suitable for evaluation of athletes performing specific skills. In addition, because single and multiple joint movements involving appropriate muscle groups can be easily performed, physiological characteristics could be evaluated for both athletic and rehabilitation purposes. Therefore, because of its simplicity of use and application, and its low cost the dynamometer would be suitable for both laboratory and field conditions. LA - English DB - MTMT ER - TY - JOUR AU - Stienen, G J M AU - Versteeg, P G A AU - Papp, Zoltán AU - Elzinga, G TI - MECHANICAL-PROPERTIES OF SKINNED RABBIT PSOAS AND SOLEUS MUSCLE-FIBERS DURING LENGTHENING - EFFECTS OF PHOSPHATE AND CA2+ JF - JOURNAL OF PHYSIOLOGY-LONDON J2 - J PHYSIOL-LONDON VL - 451 PY - 1992 SP - 503 EP - 523 PG - 21 SN - 0022-3751 UR - https://m2.mtmt.hu/api/publication/1005483 ID - 1005483 LA - English DB - MTMT ER -