Sex differences in neuromuscular control of quadriceps.

PURPOSE: Patellofemoral pain syndrome (PFPS) is twice as prevalent in females as males, yet a few studies have evaluated differences in quadriceps muscle control between sexes or across force levels. This study investigated sex differences in quadriceps EMG onset times and amplitude at different force levels during isometric knee extension in asymptomatic males and females and in females with PFPS. METHODS: Thirteen healthy males, 12 healthy females, and 10 females with PFPS performed isometric knee extension ramp contractions at 25%, 50%, and 75% of maximal voluntary contraction (MVC). Surface EMG was recorded from the vastus lateralis (VL), vastus medialis oblique (VMO), vastus medialis (VM), and rectus femoris (RF). RESULTS: Healthy females showed delayed VL (222 ± 67 ms, p = 0.002), VMO (357 ± 101 ms, p = 0.001), and VM (258 ± 62 ms, p < 0.001) recruitment in comparison with healthy males. Healthy males activated the VL earlier than the VM (156 ± 51 ms, p = 0.02) and RF (379 ± 74 ms, p < 0.001), and at a similar time as the VMO; healthy females activated the VL earlier than the VM (192 ± 53 ms, p = 0.004) and VMO (239 ± 73 ms, p = 0.01). A lower VMO:VL activation ratio was found at 25% MVC (p < 0.001) than at higher force levels. CONCLUSIONS: Delayed activation of the VMO relative to the VL has been proposed as a risk factor for PFPS. This study confirms a delay in VMO onset time in females.

The relationship between cardiac muscularis propria and clinical outcomes of peroral endoscopic myotomy in achalasia.

BACKGROUND AND AIM: Achalasia patients usually present lower esophageal sphincter thickening, which can impact the expansibility of cardia. We aimed to investigate the effect of cardiac muscularis propria (MP) on perioperative adverse events (AEs) and treatment outcomes of patients treated with peroral endoscopic myotomy (POEM). METHODS: We retrospectively reviewed 114 patients with achalasia undergoing pre-POEM endoscopic ultrasonography (EUS) between May 2013 and November 2019. Cardiac MP thickness was measured using EUS. POEM failure was defined as Eckardt score >3. Risk factors for perioperative AEs and POEM failure were identified. RESULTS: Patients were divided into the thin (n = 52) and the thick group (n = 62) based on the median of cardiac MP thickness (3.0 mm). Perioperative AEs rate of the thin group seemed to be slightly higher than that of the thick group (11.5% vs. 4.8%, P = 0.30). During a median follow-up of 30 months (range 1-77), 100 patients completed follow-up, 16 (16%) of which occurred clinical failure. The clinical outcomes of patients in the thin group were significantly poorer than those patients in the thick group (P = 0.006). Cardiac MP thickness was an independent risk factor for POEM failure (hazard ratio 3.9, P = 0.02; Cox regression), but not the risk factor for perioperative AEs (odds ratio 2.6, P = 0.2; logistic regression). CONCLUSION: Cardiac MP thickness could be a novel predictive factor for POEM failure in patients with achalasia.

Hip position and sex differences in motor unit firing patterns of the vastus medialis and vastus medialis oblique in healthy individuals.

Weakness of the vastus medialis oblique (VMO) has been proposed to explain the high prevalence of knee pain in female subjects. Clinicians commonly use exercises in an attempt to preferentially activate the VMO. Recently, our group found evidence to support clinical theory that the VMO is neurologically distinct from the vastus medialis (VM). However, the ability to voluntarily activate these muscle subsections is still disputed. The aim of this study was to determine if VM and VMO activation varies between sexes and if control of the two muscles is different between rehabilitation exercises. Thirteen men and 13 women performed isometric straight leg raises in two hip positions, neutral hip rotation and 30 degrees lateral hip rotation. Bipolar intramuscular fine-wire electrodes were inserted into the VM and VMO to obtain motor unit recruitment thresholds and initial firing rates at recruitment. Linear mixed models and Tukey post hoc tests were used to assess significant differences in 654 motor units. Women demonstrated faster motor unit firing rate at recruitment, 1.18 ± 0.56 Hz higher than men. Motor units fired 0.47 ± 0.19 Hz faster during neutral hip rotation compared with lateral hip rotation. The VMO motor units were recruited 2.92 ± 1.28% earlier than the VM. All motor units were recruited 3.74 ± 1.27% earlier during neutral hip rotation than lateral hip rotation. Thus the VM and the VMO can be activated differentially, and their motor unit recruitment properties are affected by sex and hip position. NEW & NOTEWORTHY This is the first study to reveal differential activation of the vastus medialis oblique from the vastus medialis in clinical exercise protocols. Our research group used fine-wire electrodes to examine EMG signals of the vastus medialis oblique and vastus medialis to avoid possible cross talk. We also consider the effect of sex on motor unit firing patterns because of higher prevalence of knee pain in women, and yet few studies evaluating the sex differences in neuromuscular control.

Menstrual cycle mediates vastus medialis and vastus medialis oblique muscle activity.

PURPOSE: Sports medicine professionals commonly describe two functionally different units of the vastus medialis (VM), the VM, and the vastus medialis oblique (VMO), but the anatomical support is equivocal. The functional difference of the VMO is principle to rehabilitation programs designed to alleviate anterior knee pain, a pathology that is known to have a greater occurrence in women. The purpose of this study was to determine whether the motor units of the VM and VMO are differentially recruited and if this recruitment pattern has an effect of sex or menstrual cycle phase. METHODS: Single motor unit recordings from the VM and VMO were obtained for men and women during an isometric ramp knee extension. Eleven men were tested once. Seven women were tested during five different phases of the menstrual cycle, determined by basal body temperature mapping. The recruitment threshold and the initial firing rate at recruitment were determined from 510 motor unit recordings. RESULTS: The initial firing rate was lower in the VMO than that in the VM in women (P < 0.001) but not in men. There was no difference in recruitment thresholds for the VM and VMO in either sex or across the menstrual cycle. There was a main effect of menstrual phase on initial firing rate, showing increases from the early follicular to late luteal phase (P = 0.003). The initial firing rate in the VMO was lower than that in the VM during ovulatory (P = 0.009) and midluteal (P = 0.009) phases. CONCLUSION: The relative control of the VM and VMO changes across the menstrual cycle. This could influence patellar pathologies that have a higher incidence in women.