DETERMINATION OF FASCICLE LENGTH AND PENNATION IN A CONTRACTING HUMANMUSCLE IN-VIVO

We have developed a technique to determine fascicle length in human va stus lateralis muscle in vivo by using ultrasonography. When the subje cts had the knee fully extended passively from a position of 110 degre es flexion (relaxed condition), the fascicle length decreased from 133 to 97 mm on average. During static contractions at 10% of maximal vol untary contraction strength (tensed condition), fascicle shortening wa s more pronounced (from 126 to 67 mm), especially when the knee was cl oser to full extension. Similarly as the knee was extended, the angle of pennation (fascicle angle, defined as the angle between fascicles a nd aponeurosis) increased (relaxed, from 14 to 18 degrees; tensed, fro m 14 to 21 degrees), and a greater increase in the pennation angle was observed in the tensed than in the relaxed condition when the knee wa s close to extension (<40 degrees). We conclude that there are differe nces in fascicle lengths and pennation angles when the muscle is in a relaxed and isometrically tensed conditions and that the differences a re affected by joint angles, at least at the submaximal contraction le vel.