SUMMARY1. In order to study injury-related changes in muscle stiffness, injury to the elbow flexors of thirteen human subjects was induced by a regimen of eccentric exercise.2. Passive stiffness over an intermediate range of elbow angles was measured with a device which held the relaxed arm of the subject in the horizontal plane and stepped it through the range of elbow angles from 90 deg to near full extension at 180 deg. The relation between static torque and elbow angle was quite linear over the first 50 deg and was taken as stiffness.3. Stiffness over this range of angles more than doubled immediately after exercise and remained elevated for about 4 days, and may result from low level myofibrillar activation induced by muscle stretch.4. Arm swelling was biphasic; arm circumference increased by about 3 % immediately after exercise, fell back toward normal, then increased by as much as 9 % and remained elevated for as long as 9 days.5. Ultrasound imaging showed most of the swelling immediately following the exercise to be localized to the flexor muscle compartment; subsequent swelling involved other tissue compartments as well,.6. Muscle strength declined by almost 40 % after the exercise and recovery was only slight 10 days later; the half-time of recovery appeared to be as long as 5-6 weeks.

The purpose of this investigation was to measure in vivo fascicle length (L_fas) and pennation angle (PA) of the long head of the biceps femoris muscle (BF_lh m.) at different hip and knee angles while the muscle was relaxed using ultrasonography (US). Data were collected from 18 healthy females (23.0 ± 1.8 years). To validate the measurements of the L_fas and PA, the US measurements on cadavers (n = 5), embalmed with the hip and knee in anatomical position, were compared to actual fiber lengths and PA from the dissected muscles. US images from volunteer subjects were recorded when the hip joint was positioned at 0°, 45° and 90° of hip flexion, and at each hip position, the knee joint was placed at 0°, 45° and 90° from full extension. The images were digitized to measure L_fas and PA. Results showed no significant differences between US and direct measurements of the L_fas and PA on the cadaver BF_lh m. (p > 0.05). L_fas and PA changed significantly between the different hip and knee positions in volunteer subjects (p < 0.05). Changes in the L_fas and PA are more sensitive to changes in hip position with the knee position constant than to changes in knee position with the hip position constant. This difference may be related to the larger muscle moment arm at the hip resulting in greater excursion of the muscle with changing hip position. Based on the changes in L_fas with changing joint positions, BF_lh sarcomere length was estimated to occupy a portion of the ascending limb, the plateau and descending limb of the length-tension relationship over the range of motion studied. US scanning is valid and reliable for measuring L_fas and PA of the BF_lh m. An understanding of the dynamic nature of muscle architecture will assist in determining effective and efficient clinical evaluation and rehabilitation techniques.

We performed two experiments to describe the magnitude of delayed-onset muscle soreness (DOMS) associated with blood flow restriction (BFR) exercise and to determine the contribution of the concentric (CON) versus eccentric (ECC) actions of BFR exercise on DOMS. In experiment 1, nine subjects performed three sets of unilateral knee extension BFR exercise at 35% of maximal voluntary contraction (MVC) to failure with a thigh cuff inflated 30% above brachial systolic pressure. Subjects repeated the protocol with the contralateral limb without flow restriction. Resting soreness (0-10 scale) and algometry (pain-pressure threshold; PPT) were assessed before and 24, 48 and 96 h post-exercise. Additionally, MVC and vastus lateralis cross-sectional area (CSA) were measured as indices of exercise-induced muscle damage. At 24-h post-exercise, BFR exercise resulted in more soreness than exercise without BFR (2.8 +/- 0.3 vs 1.7 +/- 0.5) and greater reductions in PPT (15.2 +/- 1.7 vs. 20 +/- 2.3 N) and MVC (14.1 +/- 2.5% decrease vs. 1.5 +/- 4.5% decrease) (p

This suggests that muscle swelling does not account for the sudden increase in stiffness of the elbow flexor muscles within the first 48 h after exercise but may play a role in the subsequent time course of stiffness.