Grey Relational Analysis of Lower Limb Muscle Fatigue and Pedalling Performance Decline of Elite Athletes during a 30-Second All-Out Sprint Cycling Exercise

The 30-second all-out sprint cycling exercise is a classical sport capacity evaluation method, which may cause severe lower limb muscle fatigue. However, the relationship between lower limb muscle fatigue and the decline in exercise performance during 30-second sprint cycling remains unclear. In this study, ten cyclists volunteered to participate in a 30-second all-out sprint cycling while power, cadence, and surface electromyographic (EMG) signals of eight lower limb muscles were recorded during the exercise. EMG mean frequency (MNF) of each lower limb muscle group was computed for every 3-second epoch based on wavelet packet transformation. Grey relational grades between pedalling performance and the EMG MNF of each lower limb muscle group during the whole process were calculated. The results demonstrated that EMG MNF of the rectus femoris (RF), vastus (VAS), gastrocnemius (GAS), and tibialis anterior (TA) progressively tired during a 30-second all-out sprint cycling exercise. Of the muscles evaluated, the degree of fatigue of TA showed the greatest association with exercise performance decline, whereas the muscle fatigue of RF, VAS, and GAS also significantly impacted exercise performance during a 30-second all-out sprint cycling exercise.

Submaximal isometric fatiguing exercise of the elbow flexors has no age-related effect on GABAB mediated inhibition

Age-related changes in the neuromuscular system can result in differences in fatigability between young and older adults. Previous research has shown that single joint isometric fatiguing exercise of small muscle results in an age-related compensatory decrease in GABAB mediated inhibition. However, this has yet to be established in a larger muscle group. In 15 young (22 ± 4 years) and 15 older (65 ± 5 years) adults, long interval cortical inhibition (LICI; 100 ms ISI) and corticospinal silent period (SP) were measured in the biceps brachii during a 5% EMG contraction using transcranial magnetic stimulation (TMS) before, during and after a submaximal contraction (30% MVC force) held intermittently to task failure. Both age groups developed similar magnitude of fatigue (~24% decline in MVC; P = 0.001) and ~28% decline in LICI (P = 0.001) post fatiguing exercise. No change in SP duration was observed during and immediately following fatigue (P = 0.909) but ~ 6% decrease was seen at recovery in both age groups (P<0.001)." Contrary to previous work in a small muscle, these findings suggest no age-related differences in GABAB mediated inhibition following single joint isometric fatiguing exercise of the elbow flexors, indicating that GABAB modulation with ageing may be muscle group dependent. Furthermore, variations in SP duration and LICI modulation during and post fatigue in both groups suggest that these measures are likely mediated by divergent mechanisms.

Functional Recovery after Revision Anterior Cruciate Ligament Reconstruction with a Second Autograft: A Matched Cohort Analysis in Adolescent Patients (197)

Objectives: Young patients are the highest risk demographic for ACL graft failure and revision surgery. Previous studies have shown higher rates of graft failure with the use of allograft tissue for ACL reconstruction (ACLR) in both primary and revision surgeries. However, questions remain regarding the functional consequence of harvesting a second autograft from the ipsilateral knee for revision ACLR. The purpose of this study was to evaluate 6-month functional testing in patients who underwent revision ACLR with use of a second autograft from the ispilateral knee, when compared to matched cohorts of primary ACLR patients. Methods: A retrospective review of prospectively collected data from patients aged 19 or younger who underwent revision ACLR with a second autograft of an opposite muscle group (either revision patellar tendon (BTB) following primary hamstring (HS) or revision HS following primary BTB) at the study institution was performed. Exclusion criteria were patients who underwent iliotibial band autograft ACLR, those with two autografts from synergistic muscle groups, grafts from the contralateral knee, debilitating injury or surgery to the contralateral lower extremity, and multi-ligamentous knee injury. All subjects underwent functional return to sports (RTS) testing 5-8 months after revision surgery, which included anthropometric measures, isometric strength, Y-Balance, and functional hop testing. Side-to-side deficits were then compared using standard limb symmetry index (LSI) metrics, after matching a cohort of primary ACLR patients based on age, sex, and body mass index (BMI). Multivariate analysis of variance (MANOVA) was used to compare RTS metrics, and if significance was detected, pairwise comparison was performed by Bonferroni post-hoc correction. Statistical significance of p<0.05 was applied. Results: The cohort of 37 revision ACLR patients were compared to cohorts of 62 primary HS and 47 BTB ACLR patients, respectively (Table 1). The revision cohort showed comparable knee extension strength deficits to the BTB cohort (-9.45±12.09% vs -8.81±13.83%, p=0.999), which were significantly greater than that of the HS cohort (-9.45±12.09% vs -0.99±12.00%, p<0.05). Greater knee flexion strength deficits were seen in the HS cohort than the revision cohort (-38.90±16.21% vs -28.13±23.22%, p=0.009), whose deficits were, in kind, significantly greater than that of the BTB cohort (-28.13±23.22% vs -1.17±12.41%, p=0.001). The HS cohort also showed greater triple hop deficit (-21.08±25.99%) than the other two cohorts (-21.08±25.99% vs -10.75±12.85 vs -6.84±23.81, p=0.024), which were not significantly different from each other. Conclusions: After revision ACLR with a second autograft from the opposing muscle group of the ipsilateral knee, adolescents show similar knee extension strength deficits compared to primary ACLR patients with BTB grafts, but improved knee flexion strength deficits compared to primary ACLR patients with HS grafts.

Experimental Studies of Carpenter Bee (Xylocopa: Apidae) Thorax Mechanics During Defensive Buzzing

Bees and other Hymenoptera utilize thorax vibration to realize an extensive range of behaviors ranging from flight to pollination. Strong indirect flight muscles contract to deform the thoracic walls and the resulting oscillation is sustained through a mechanism called stretch activation. While the mechanics of the insect thorax and muscles have been studied extensively during flight, relatively little is known about the thorax mechanics during non-flight behaviors. In this work, we investigate the thorax mechanics of the carpenter bee Xylocopa californica during defensive buzzing. During defensive buzzing, the insect folds its wings over its abdomen and rapidly fires it flight muscles, resulting in a loud audible buzz and large forces intended to deter predators. We devised a novel experiment to measure thorax oscillation and directional force production from a defensively buzzing carpenter bee. The largest peak forces were on average 175 mN and were oriented with the insect's dorsal-ventral muscle group. Peak forces oriented with the insect's dorsal-longitudinal muscle group averaged 117 mN. Thorax velocities were about 90 mm s^-1 p-p and velocity amplitude was positively correlated to peak force. Thorax oscillation frequency averaged 132 Hz but was highly variable both within individuals and across the tested population. From our measurements, we estimated the peak mechanical power required by defensive buzzing at 8.7 mW, which we hypothesize is greater than the power required during flight. Overall, this study provides insight into the function and capabilities of the Hymenopteran indirect flight muscle during non-flight behaviors.

Muscle group specific transcriptomic and DNA methylation differences related to developmental patterning in FSHD

Muscle groups throughout the body are specialized in function and are specified during development by position specific gene regulatory networks. In developed tissue, myopathies affect muscle groups differently. Facioscapulohumeral muscular dystrophy, FSHD, affects upper body and tibialis anterior (TA) muscles earlier and more severely than others such as quadriceps. To investigate an epigenetic basis for susceptibility of certain muscle groups to disease, we perform DNA methylation and RNA sequencing on primary patient derived myoblasts from TA and quadricep for both control and FSHD2 as well as RNA-seq for myoblasts from FSHD1 deltoid, bicep and TA over a time course of differentiation. We find that TA and quadricep retain methylation and expression differences in transcription factors that are key to muscle group specification during embryogenesis. FSHD2 patients have differences in DNA methylation and expression related to SMCHD1 mutations and FGF signaling. Genes induced specifically in FSHD are more highly expressed in commonly affected muscle groups. We find a set of genes that distinguish more susceptible muscle groups including development-associated TFs and genes involved in WNT signaling. Adult muscle groups therefore retain transcriptional and DNA methylation differences associated with development, which may contribute to susceptibility in FSHD.