Electromyographic Comparison Between the Rear-Foot-Elevated vs. B-Stance Unilateral Back Squat Techniques

The Rear-Foot-Elevated back squat (RFE) and B-Stance (BS) are two unilateral back squat techniques with the latter commonly proposed as the more stable of the two. There is currently a lack of research comparing these two techniques with respect to neuromuscular demand and movement characteristics. PURPOSE: The purpose of this study was to examine the muscle activation differences via surface electromyography (EMG) between the RFE vs. BS unilateral back squat techniques with equated load. METHODS: Thirteen healthy college-aged, resistance-trained male (n=10) and female (n=3) subjects were recruited for this study. Subjects visited the laboratory on two occasions separated by 5-7 days. Visit 1 included descriptive measurements and one-repetition max (1RM) testing for the RFE back squat. For visit 2, subjects performed the RFE and BS unilateral squat techniques under a load of 85% of RFE 1RM. Electromyographic assessment of the external oblique (OBL), rectus femoris (RF), gluteus maximums (GM) and biceps femoris (BF) was administered during each technique and subsequently compared. RESULTS: A paired sample t-test was used to compare mean and peak normalized root mean square (RMS) EMG between the RFE and BS techniques. There was no significant difference in mean and peak eccentric, concentric, and total activation between the RFE vs. BS for the OBL and RF. For GM, mean and peak eccentric, concentric, and total activation was greater during the RFE vs. BS (pCONCLUSION: The RFE unilateral back squat technique elicited overall greater activation of the hip extensors, GM and BF vs. BS. Based on these findings, the two unilateral squat techniques are not interchangeable from a muscle activation perspective which should be considered when employing unilateral back squat variations in training or rehabilitation programs

Electromyographic Examination of Hip and Knee Extension Hex Bar Exercises Varied by Starting Knee and Torso Angles

International Journal of Exercise Science 15(1): 541-551, 2022. Variations of the deadlift can be executed using the hexagonal (hex) bar by altering, for instance, the knee and torso angles while maintaining a constant hip angle at the start position. PURPOSE: To examine muscle activation patterns of the biceps femoris, rectus femoris, and erector spinae during three deadlift variations using the hex bar. METHODS: Twenty resistance-trained male and female subjects performed hex bar deadlift variations in three different starting knee flexion positions: 128.4 ± 8.5°, 111.9 ± 8.7°, and 98.3 ± 6.5°. Subjects performed three repetitions at 75% of their three-repetition maximum. Electromyography sensors were placed on the dominant biceps femoris, rectus femoris, and lumbar erector spinae. A one-way repeated measures ANOVA was used to detect differences in mean and peak EMG values normalized to maximum voluntary isometric contraction (MVIC) (p \u3c 0.05). RESULTS: As knee flexion increased at the starting position, mean activation of the rectus femoris increased (24.7 ± 21.5 35.5 ± 25.4 62.1 ± 31.3% MVIC, p \u3c 0.001), while biceps femoris (40.6 ± 17.9 34.0 ± 16.4 28.1 ± 14.5% MVIC, p = 0.003) and erector spinae (73.0 ± 27.6 65.9 ± 34.4 54.9 ± 32.5% MVIC, p = 0.009) activation decreased. Peak activation of the rectus femoris increased (46.9 ± 33.0 60.9 ± 38.7 99.3 ± 41.6% MVIC, p \u3c 0.001) while decreasing in the erector spinae (118.6 ± 47.1 105.9 ± 49.4 89.1 ± 40.1% MVIC, p = 0.008). The rectus femoris experienced the greatest mean differences of the three muscles. CONCLUSIONS: Practitioners should consider the muscular goals when adjusting the starting position of a hex bar deadlift as posterior chain recruitment diminished and quadriceps activation increased as knee flexion increased

The clinical features of juvenile dermatomyositis: A single-centre inception cohort

Introduction: Juvenile Dermatomyositis (JDM), a severe and rare autoimmune disease, is the most common idiopathic inflammatory myopathy in children. We describe the clinical features of a large single-centre cohort.Methods: We studied an inception cohort (0-18 years old) referred for diagnosis to the JDM clinic at The Hospital for Sick Children (SickKids), between January 1989 and September 2017. Probable or definite diagnosis of JDM was done according to the 2017 ACR/EULAR Criteria. We excluded children who had treatment started at another hospital. The data were collected retrospectively from clinical charts and the SickKids JDM database.Results: 172/230 (74.8%) patients were included. They were most often female (female:male = 1.8:1); the age at diagnosis was 8.5 +/- 4.3 years. There was a positive family history for autoimmune disease in 52%, mainly rheumatoid arthritis. No patient died. The most common signs at inception were muscle weakness (85.5%), nailfold capillary abnormalities (83.4%), Gottron papules (78.5%), heliotrope rash (66.3%), abnormal gait (55.8%), and malar/facial rash (54.7%). The prevalence of Gottron papules, heliotrope rash, facial/malar rash, nailfold capillary abnormalities, Raynaud phenomenon, dysphonia/dysphagia (a frequent cause of hospitaliza-tion), mouth ulcers, calcinosis, eye problems, joint involvement, acanthosis nigricans and lipodystrophy increased during follow-up. Muscle enzymes, namely CK, ALT, AST, were often normal or only slightly raised despite active muscle disease; conversely LD was often high. Anti-Nuclear Autoantibodies were positive in 49.7% of patients at diagnosis. The course of the disease was: 29.1% monocyclic, 5.3% polycyclic, 33.1% chronic. The course of 56 patients (32.5%) was not classifiable due to length of follow-up. Corticosteroids were used as treatment in almost all our patients and 30% required intravenous therapy due to the severity of the presen-tation; methotrexate was added in 64%, more often in recent years. Unresponsive patients were treated mostly with intravenous immunoglobulins (IVIG).Conclusions: The information obtained from this relatively large number of patients adds to the growing knowledge base of this rare disease. Trial registration: SickKids Research Ethics Board approved the study

Iridescence impairs object recognition in bumblebees

AbstractIridescence is a taxonomically widespread and striking form of animal coloration, yet despite advances in understanding its mechanism, its function and adaptive value are poorly understood. We test a counterintuitive hypothesis about the function of iridescence: that it can act as camouflage through interference with object recognition. Using an established insect visual model (Bombus terrestris), we demonstrate that both diffraction grating and multilayer iridescence impair shape recognition (although not the more subtle form of diffraction grating seen in some flowers), supporting the idea that both strategies can be effective means of camouflage. We conclude that iridescence produces visual signals that can confuse potential predators, and this might explain the high frequency of iridescence in many animal taxa.</jats:p