Distribution of motor unit potential velocities in the biceps brachii muscle of sprinters and endurance athletes during short static contractions at low force levels

Chronic fatigue syndrome: Abnormally fast muscle fiber conduction in the membranes of motor units at low static force load

OBJECTIVE

Chronic fatigue syndrome (CFS) and fibromyalgia (FM) are disorders of unknown etiology and unclear pathophysiology, with overlapping symptoms of - especially muscular -fatigue and pain. Studies have shown increased muscle fiber conduction velocity (CV) in the non-painful muscles of FM patients. We investigated whether CFS patients also show CV abnormalities.

METHODS

Females with CFS (n = 25), with FM (n = 22), and healthy controls (n = 21) underwent surface electromyography of the biceps brachii, loaded up to 20% of maximum strength, during short static contractions. The mean CV and motor unit potential (MUP) velocities with their statistical distribution were measured.

RESULTS

The CV changes with force differed between CFS-group and both FM-group and controls (P = 0.01). The CV of the CFS-group increased excessively with force (P < 0.001), whereas that of the controls increased only slightly and non-significantly, and that of the FM-group did not increase at all. In the CFS-group, the number of MUPs conveying very high conduction velocities increased abundantly with force and the MUPs narrowed.

CONCLUSION

Our results suggest disturbed muscle membrane function in CFS patients, in their motor units involved in low force generation. Central neural deregulation may contribute to this disturbance.

SIGNIFICANCE

These findings help to detangle the underlying mechanisms of CFS.

The Relationship Between a Jump-Landing Task and Functional Movement Screen Items : A Validation Study

Kraus, K, Schütz, E, and Doyscher, R. The relationship between a jump-landing task and functional movement screen items : a validation study. J Strength Cond Res 33(7): 1855-1863, 2019-Sports injuries and athletic performance are complex areas, which are characterized by manifold interdependencies. The landing error scoring system (LESS) is a valid screening tool to examine bilateral jump-landing mechanics, whereas the Functional Movement Screen (FMS) items are thought to operationalize flexibility and motor behavior during low-intense bodyweight patterns. The aim of the study was to explore possible interdependency of the diagnostic information of these screening tools. Fifty-three athletes (age 23.3 ± 2.1 years) were tested in a sport scientific laboratory. In detail, 31 professional soccer players (third division) and 22 collegiate athletes were studied. Linear, partial correlational, and cluster analysis were performed to examine possible trends. Generally, the sportsmen achieved a LESS score of 6.6 ± 2 and a jumping height of 37 ± 7.8 cm. Partial correlational analysis indicates that trunk control (r = 0.4; p < 0.01) is moderately related to landing mechanics, which in turn was negatively related on LESS height (r = -0.67, p < 0.01). In addition, clustering showed by trend that a higher active straight leg raise (ASLR) score is related to better landing mechanics (ASLR score 1: LESS 6.9 ± 1.8; n = 15 vs. ASLR score 3: LESS 5.6 ± 2.1; n = 10). On the task-specific level, jump-landing mechanics were directly related to jumping performance in this cohort with poor mechanics. On unspecific analysis level, kinetic chain length (ASLR) and trunk control have been identified as potential moderator variables for landing mechanics, indicating that these parameters can limit landing mechanics and ought to be optimized within the individual's context. A potential cognitive strategy shift from internal (FMS) to external focus (LESS) and different muscle recruitment patterns are potential explanations for the nonsignificant linear relationship between the FMS and LESS data.