In vivo measurement of fascicle length and pennation angle of the human biceps femoris muscle.

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 degrees, 45 degrees and 90 degrees of hip flexion, and at each hip position, the knee joint was placed at 0 degrees, 45 degrees and 90 degrees 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.

Effect of cessation and resumption of static hamstring muscle stretching on joint range of motion.

STUDY DESIGN: Single group repeated measures. OBJECTIVES: To determine the effects of cessation and resumption of a hamstring muscle stretching protocol on knee range of motion (ROM). BACKGROUND: It is generally accepted that stretching exercises result in an increase in ROM. The ability to maintain ROM once stretching has ceased and the ability to regain ROM after resumption of the stretching exercise is not well-known. METHODS AND MEASURES: Evaluated the effect of 6 weeks of static hamstring stretching, 4 weeks with cessation from stretching, and 6 weeks with resumption of stretching on knee ROM in 18 inactive college students (12 men, 6 women, mean age 21.0 years). The hamstring stretching consisted of 2 30-second stretches per day, 5 days per week. Knee ROM was measured before and after each of the above phases with an active knee extension test. RESULTS: Mean knee ROM increased after the initial stretching period (143+/-11 to 152+/-9 degrees), decreased to baseline following the cessation period (145+/-8 degrees) and again increased following the resumption of stretching but was not different from the initial gains (154+/-10 degrees). Unlike the stretch limb, the control limb ROM did not change over the 4 measurement times. CONCLUSIONS: There was no retention of knee ROM 4 weeks following a 6-week stretching protocol and a subsequent stretching period did not enhance the gain of knee ROM over the initial stretching period.

Relationship between muscle swelling and stiffness after eccentric exercise.

PURPOSE: The time courses of muscle compartmental swelling and passive stiffness change were measured to determine whether muscle compartmental swelling accounted for increased stiffness. METHODS: Eleven untrained female college students exercised eccentrically by lowering a weight with their elbow flexors. Measurements of muscle compartment volume, stiffness, relaxed elbow angle, circumference, and pain were recorded before exercise, immediately after exercise, and 1-5, 7, 9, and 11 d after exercise. Muscle compartment volume was calculated from cross-sectional ultrasound images taken along the upper arm. Stiffness was measured using a device that extended the elbow and recorded the torque required to hold the forearm at successive angles. RESULTS: Elbow flexor volume increased gradually to peak on the fourth day (26.1 +/- 4.3%, P < 0.05) and then decreased to baseline values over days 7-11. Stiffness increased immediately after exercise (59.9 +/- 14.1%, P < 0.05) and remained at or above this level until decreasing to pre-exercise levels over days 7-11. CONCLUSIONS: 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.

Skeletal muscle architecture and fiber-type distribution with the multiple bellies of the mouse extensor digitorum longus muscle.

The purpose of this study was to describe the extent to which architectural and fiber-type characteristics of the four bellies of the mouse extensor digitorum longus (EDL) suggest specialization of the digits, and to mathematically model the functional effects of the structural properties. Six mice were perfused in situ with glutaraldehyde while the lower limb was positioned approximately in the neutral position. After perfusion, lower limbs were removed and placed in glutaraldehyde until the EDL was dissected from the limb and separated into individual muscle bellies corresponding to each digit for architectural determination. The results showed that the muscle belly of digit 5 tended to be different from the muscle bellies of digits 2-4 for many architectural characteristics. Muscle mass, physiological cross-sectional area, muscle length, and fiber length were all significantly greater in digit 5. Proximal tendon length was also significantly longer in digit 5, and distal tendon length, as well as total tendon length, were significantly shorter in digit 5. Sarcomere length was shortest at the proximal end of the muscle and longest, 60-80%, toward the distal end. Fiber type distribution was about 60% FOG, 39% FG with only 1% SO fibers in all muscle bellies. Muscle-tendon modeling illustrated that peak force and maximal shortening velocity were greatest in digit 5. Inclusion of the tendon in the model resulted in a 10% shift of the force-length curve to longer lengths. Assuming muscle structure is matched to function, we speculate that digit 5 of the mouse EDL bears higher loads over a greater excursion during locomotion compared to the remaining digits.

Intermittent pneumatic compression effect on eccentric exercise-induced swelling, stiffness, and strength loss.

OBJECTIVE: The purpose was to determine if intermittent pneumatic compression (IPC) affects muscle swelling, stiffness, and strength loss resulting from eccentric exercise-induced injury of the elbow flexors. We hypothesized that the compression would decrease swelling and stiffness. DESIGN: Repeated measures design with a before-after trial comparison within each day. SETTING: Conducted at a university Somatic Dysfunction Laboratory. SUBJECTS: Twenty-two college women students were studied. They had not been lifting weights or otherwise participating in regular arm exercise for the 6 months before the study. They had no history of upper extremity injury or cardiovascular disease. INTERVENTIONS: Subjects performed one bout of eccentric exercise at a high load to induce elbow flexor muscle injury. Uniform IPC was applied on the day of exercise and daily for 5 days at 60mmHg, 40 seconds inflation, 20 deflation for 20 minutes. MAIN OUTCOME MEASURES: Measurements of arm circumference, stiffness, and isometric strength were recorded before exercise, then before and after IPC for 5 days after exercise. Passive muscle stiffness was measured on a device that extends the elbow stepwise and records the torque required to hold the forearm at each elbow angle. RESULTS: Circumference and stiffness increased and strength decreased during the 5 days post-exercise (p < .05). IPC significantly decreased circumference and stiffness most notably on days 2 and 3 after exercise (p < .05). The strength loss was not affected by IPC. CONCLUSION: IPC is effective in temporarily decreasing the swelling and stiffness after exercise-induced muscle injury.