Modifications Of Joint Mobility Range Induced By Eccentric Contraction

Dynamic eccentric contraction causes muscle damage consisting of: myofibrills disorganization, Z-lines disruption and cell membrane lesions. This damage is indirectly evidenced by a massive, delayed (4th-5th day) CK release in the serum. Negative work induces also a clinical condition defined as "Delayed Onset Muscle Soreness" (DaMS), characterized by delayed onset (8-24h) muscle pain, lowering in muscle pain threshold (24-4Bh), swelling of the exerted limb (72h). Stiffness and restricted range of movement in the joints related to the exerted muscles are also described, but the phenomena are less investigasted. The aim of this study was to evaluate the range of knee joint mobility before and after a standardized eccentric effort. Twelve healthy runners, aged 24-35 years, were examined. They performed a step-test (20' duration, 15 cycles/min), to exert the quadriceps femoris muscle of one side eccentrically. The day before the test, all the subjects underwent evaluation of Pressure Pain Threshold (PPT) of the exerted muscle and Passive Joint Mobility (PJM) of the knee. These evaluations were repeated immediately after the test and on the following 6 days; on the same days, the perceived pain was also measured by means of a force-transducer equipped with a 2.5 cm diameter rounded probe and a digital analyser (unit:Kg/f), applied on 12 pre-established spots on the quadriceps muscle surface; the mean of the 12 recordings was taken as, the final threshold value. PJM was measured by means of a manual goniometer on prone subjects; the exerted lower limb was moved from the rest position to the maxmal pain-free flexion; the degree at which the subject felt the minimum discomfort was recorded. Student's "ttest" for paired data was employed for statistical analysis. PPT showed a significant decrease after 24 and 4Bh in the exerted muscle, while pain reached maximum value at the 4Bh measurement. PJM showed a significant reduction 24-72h after the effort. DaMS is a complex phenomena, whose explanation is still unclear; particularly the temporal dissociation between symptoms and signs of muscle damage. The reduction of PJM has been attributed to edema of the connective tissue, due to the eccentric contraction stress. However the maximal thickness of the eccentrically exerted limb is usually found at 72h, while the reduction of PJM starts at 24h. The results of the present study show that the temporal pattern of PJM reduction is fairly similar to that of pain and hyperalgesia. This could suggest a reflex origin of the phenomenon, due to painful symptoms, through a tonic activation of antagonist muscles