1. The relationship between joint damage, quadriceps weakness and arthrogenic muscle inhibition was investigated in eight patients who had sustained extensive traumatic knee injury. Isometric and isokinetic quadriceps and hamstring voluntary strength, and quadriceps arthrogenic muscle inhibition during isometric contractions, were measured before and after 4 weeks (approximately 100 h) of intensive rehabilitation. 2. Compared with the uninjured leg, before rehabilitation the injured leg had larger amounts of quadriceps arthrogenic muscle inhibition ( P < 0.025), quadriceps ( P < 0.0001) and hamstring ( P < 0.0001) weakness and severe functional joint instability. There was a negative correlation between the amount of arthrogenic muscle inhibition and quadriceps voluntary contraction force ( P < 0.025). 3. After rehabilitation in the injured leg there were small hamstring strength increases ( P < 0.05–0.025), but no overall significant quadricep strength increase. Arthrogenic muscle inhibition was statistically unchanged. Severe functional joint instability was still reported by all patients. 4. Previous studies have shown that minimal joint damage evokes relatively less arthrogenic muscle inhibition that does not impede rehabilitation. These data indicate that greater joint damage is associated with greater arthrogenic muscle inhibition, quadriceps weakness and joint instability. Furthermore, intensive rehabilitation had little affect on either quadriceps arthrogenic muscle inhibition or atrophy.
1. The effect of muscle length on the development of muscle pain and fatigue has been studied. 2. Eight normal young adults performed maximal eccentric contractions of the elbow flexors. The muscles of one arm were exercised at short length, and the contralateral muscle at long length. Each contraction lasted approximately 1 s, and was repeated once every 10 s for 30 min. 3. Muscle strength and frequency-force characteristics were measured from isometric contractions before, immediately after and at 24 h intervals for the next 4 days. Muscle tenderness was assessed daily. 4. The muscle strength was reduced by approximately 10% by exercise at short length, and by 30% by exercise at long length. 5. The 20:100 ratio (force generated by stimulation at 20 Hz/force generated at 100 Hz) fell by 30% after exercise at short length and had recovered after 24 h. Exercise at long length reduced this ratio by 65% and the muscles had not fully recovered 4 days later. 6. Muscle pain developed after both exercise regimens, but was slightly worse after that at long length. 7. It is concluded that there is a length-dependent component in the development of pain and fatigue after eccentric exercise, which had previously been thought to be caused solely by high force generation.
1. Skeletal muscle strength, contractile properties and radiological composition have been studied in seven morbidly obese adults (six female) before and 1 year after gastroplasty operations. The mean body weight fell from 138.3 kg ( sd 25.2) to 99.7 kg ( sd 23.0) ( P < 0.001). 2. The strength and contractile properties (force/frequency, relaxation rate and fatiguability) of both the adductor pollicis and quadriceps muscles were unaffected by the weight loss. 3. Computerized axial tomography scans obtained 1 year after surgery showed that the quadriceps contained an abnormally high proportion of fat. The mean fat content was 10.8% (range 3.0–30.1%) compared with 1.6% (range 0–5%) for normal muscle. Two individuals were scanned before and after surgery and the fat content of their quadriceps fell from 12.6% and 6.9% to 3.1% and 3.0%, respectively. 4. It is concluded that in obese individuals large amounts of weight can be lost, from both subcutaneous and intramuscular fat stores, without compromising either the strength or contractile properties of skeletal muscles. These results do not support the claim that skeletal muscle contractility is a sensitive indicator of changes in nutritional status.
1. Normal subjects performed a step test in which the quadriceps of one leg contracted concentrically while the contralateral muscle contracted eccentrically. 2. Maximal voluntary force and the force:frequency relationship were altered bilaterally as a result of the exercise, the changes being greater in the muscle which had contracted eccentrically. Recovery occurred over 24 h. 3. Electromyographic studies using three sites on each muscle showed an increase in electrical activation during the exercise only in the muscle which was contracting eccentrically. Recovery followed a time course similar to that of the contractile properties. 4. Pain and tenderness developed only in the muscle which had contracted eccentrically. Pain was first noted approximately 8 h after exercise and was maximal at approximately 48 h after exercise, at which time force generation and electrical activation had returned to pre-exercise values. 5. Eccentric contractions cause more profound changes in some aspects of muscle function than concentric contractions. These changes cannot be explained in simple metabolic terms, and it is suggested that they are the result of mechanical trauma caused by the high tension generated in relatively few active fibres during eccentric contractions.