The fitness of a group of individuals of various ages and both genders was asses
ID: 61327 • Letter: T
Question
The fitness of a group of individuals of various ages and both genders was assessed in a step test. The test consisted of stepping up and down 18 inches (46 cm) 15 times per minute, for twenty minutes. The stepping pattern produced shortening of the right quadriceps muscle during the step up. The descent was opposed by contraction of the left quadriceps muscle that was stretched by the force of gravity. The subjects reported feeling weakness in the left quadriceps muscle. The weakness lasted for approximately 2 hours, and maximum voluntary force development was less than the preexercise value. Percutaneous electrical stimulation of the quadriceps elicited reduced forces. Pain developed in the left quadriceps 8 to 10 hours after the exercise, reached maximal intensity between 24 and 48 hours, and persisted for about a week. This delayed onset of muscular soreness (DOMS) induced by exercise was marked in the activities that imposed negative work on the muscle; such activities include descending stairs. The magnitude of the soreness was unrelated to the overall fitness of the individuals, but specific training for this step test prevents soreness in subsequent tests. Evidence of muscle cell injury included an increase in serum levels of soluble proteins, such as creatine kinase and myoglobin. The time course was similar to that of the soreness. Myofibrillar disorganization and sarcolemmal disruption could be observed in biopsy sample from only the left quadriceps.
1. Have you experienced DOMS? What are the circumstances that lead to DOMS and increase its severity?
2. Why was DOMS experienced in only the left quadriceps muscle in this fairly moderate exercise?
3. Is an impaired adenosine triphosphate (ATP) supply or synthetic capacity a reasonable explanation for the fatigue of the left quadriceps muscle?
4. One hypothesis for the etiology of DOMS is that increased metabolism results in the accumulation of toxic waste products. Can this explain the soreness?
5. Exercise can raise the temperature of an active muscle by 5° C or more. Is heat injury a plausible explanation for DOMS?
6. Are there clinical signs of a muscle cell injury?
7. What is a plausible mechanism for injury of muscle cells or their tendons?
8. What does DOMS suggest about the adaptability of muscle fibers to use?
9. Pain is usually regarded (teleologically) as a signal to protect the organism from injury. Is this rational explanation for DOMS?
10. What might be responsible for the slow development of stiffness and soreness?
Explanation / Answer
1. Yes, we experience DOMS (delayed onset of muscular soreness) after a period of exercise. This is because of forced and sustained use of muscles (as in case of descending stairs). Increased intensity of effort still increase the severity of DOMS,
2. During descending, the Gravity impose forces on the left quadriceps, because attached cross bridges in left quadriceps muscle (descent was opposed by contraction of the left quadriceps muscle that was stretched by the force of gravity) can bear more load than the force that they can develop. As a result, the forces on the motor units of the left quadriceps muscle would be greater than the forces in the right quadriceps muscle.
3. Yes, the impaired adenosine triphosphate supply responsible for the left quadriceps muscle fatigue.
4. Increased metabolism produces lactic acid in muscle tissue, which with results in muscle soreness.