Effects of Neuromuscular Electrical Stimulation Training on Endurance Performance

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Hip muscle weakness in patients with symptomatic femoroacetabular impingement

SummaryObjectiveFemoroacetabular impingement (FAI) is a pathomechanical process, which may cause hip pain, disability and early development of hip osteoarthritis (OA) in young and active adults. Patients with FAI experience functional disability during dynamic weight-bearing activities, which could originate from weakness of the hip muscles. The objective of this study was to compare hip muscle strength between patients with symptomatic FAI and healthy controls. It was hypothesized that patients would present overall hip muscle weakness compared to controls.MethodsA total of 22 FAI patients and 22 controls matched for gender, age, and body mass participated in the study. We evaluated isometric maximal voluntary contraction (MVC) strength of all hip muscle groups using hand-held and isokinetic dynamometry, and electromyographic (EMG) activity of the rectus femoris (RF) and tensor fasciae latae (TFL) muscles during active flexion of the hip.ResultsFAI patients had significantly lower MVC strength than controls for hip adduction (28%), flexion (26%), external rotation (18%) and abduction (11%). TFL EMG activity was significantly lower in FAI patients compared with controls (P=0.048), while RF EMG activity did not differ significantly between the two groups (P=0.056).ConclusionsPatients with symptomatic FAI presented muscle weakness for all hip muscle groups, except for internal rotators and extensors. Based on EMG recordings, it was demonstrated that patients with symptomatic FAI have a reduced ability to activate TFL muscle during hip flexion. These findings provide orthopedic surgeons with objective information about the amount and specificity of hip muscle weakness in patients with FAI. Future research should investigate the relationship between hip muscle weakness, functional disability and overuse injury risks, as well as the effects of hip muscle strengthening on clinical outcomes in individuals with symptomatic FAI

Peripheral Muscle Function During Repeated Changes of Direction in Basketball

PURPOSE: To examine differences between adult male basketball players of different competitive levels (study 1) and changes over a basketball season (study 2) of knee extensor peripheral muscle function during a multi-stage changes of direction exercise (MCODE). METHODS: In study 1, 111 players from 4 different divisions completed the MCODE during the regular season. In study 2, the MCODE was performed before (T1) and after (T2) the preparation period and during the competitive season (T3) by 32 players from division I, II and III. The MCODE comprised 4 levels of increasing intensity for each player. The peak twitch torque (PT) of knee extensors was measured after each level. PTmax (the highest value of PT) and fatigue were calculated. RESULTS: In study 1, we found possibly small differences (ES\ub190%CI: -0.24\ub10.39) in fatigue between division I and II. Division I was characterized by likely (ES: 0.30 to 0.65) and very likely-to-almost certain (ES: 0.74 to 1.41) better PTmax and fatigue levels compared to division III and VI, respectively. In study 2, fatigue was very likely reduced (ES: -0.91 to -0.51) among all divisions from T1 to T2, while PTmax was likely-to-very likely reduced (ES: -0.51 to -0.39) in division II and III. CONCLUSIONS: Professional basketball players are characterized by a better peripheral muscle function during a MCODE. Most of the seasonal changes in peripheral muscle function occurred after the preparation period. These findings inform practitioners on the development of training programs to enhance the ability to sustain repeated changes of direction efforts

Responders to Wide-Pulse, High-Frequency Neuromuscular Electrical Stimulation Show Reduced Metabolic Demand: A 31P-MRS Study in Humans.

Conventional (CONV) neuromuscular electrical stimulation (NMES) (i.e., short pulse duration, low frequencies) induces a higher energetic response as compared to voluntary contractions (VOL). In contrast, wide-pulse, high-frequency (WPHF) NMES might elicit-at least in some subjects (i.e., responders)-a different motor unit recruitment compared to CONV that resembles the physiological muscle activation pattern of VOL. We therefore hypothesized that for these responder subjects, the metabolic demand of WPHF would be lower than CONV and comparable to VOL. 18 healthy subjects performed isometric plantar flexions at 10% of their maximal voluntary contraction force for CONV (25 Hz, 0.05 ms), WPHF (100 Hz, 1 ms) and VOL protocols. For each protocol, force time integral (FTI) was quantified and subjects were classified as responders and non-responders to WPHF based on k-means clustering analysis. Furthermore, a fatigue index based on FTI loss at the end of each protocol compared with the beginning of the protocol was calculated. Phosphocreatine depletion (ΔPCr) was assessed using 31P magnetic resonance spectroscopy. Responders developed four times higher FTI's during WPHF (99 ± 37 ×103 N.s) than non-responders (26 ± 12 ×103 N.s). For both responders and non-responders, CONV was metabolically more demanding than VOL when ΔPCr was expressed relative to the FTI. Only for the responder group, the ∆PCr/FTI ratio of WPHF (0.74 ± 0.19 M/N.s) was significantly lower compared to CONV (1.48 ± 0.46 M/N.s) but similar to VOL (0.65 ± 0.21 M/N.s). Moreover, the fatigue index was not different between WPHF (-16%) and CONV (-25%) for the responders. WPHF could therefore be considered as the less demanding NMES modality-at least in this subgroup of subjects-by possibly exhibiting a muscle activation pattern similar to VOL contractions

Statistical shape modeling of the hip and the association with hip osteoarthritis: a systematic review

Objective: To summarize available evidence on the association between hip shape as quantified by statistical shape modeling (SSM) and the incidence or progression of hip osteoarthritis. Design: We conducted a systematic search of five electronic databases, based on a registered protocol (available: PROSPERO CRD42020145411). Articles presenting original data on the longitudinal relationship between radiographic hip shape (quantified by SSM) and hip OA were eligible. Quantitative meta-analysis was precluded because of the use of different SSM models across studies. We used the Newcastle–Ottawa Scale (NOS) for risk of bias assessment. Results: Nine studies (6,483 hips analyzed with SSM) were included in this review. The SSM models used to describe hip shape ranged from 16 points on the femoral head to 85 points on the proximal femur and hemipelvis. Multiple hip shape features and combinations thereof were associated with incident or progressive hip OA. Shape variants that seemed to be consistently associated with hip OA across studies were acetabular dysplasia, cam morphology, and deviations in acetabular version (either excessive anteversion or retroversion). Conclusions: Various radiographic, SSM-defined hip shape features are associated with hip OA. Some hip shape features only seem to increase the risk for hip OA when combined together. The heterogeneity of the used SSM models across studies precludes the estimation of pooled effect sizes. Further studies using the same SSM model and definition of hip OA are needed to allow for the comparison of outcomes across studies, and to validate the found associations

Actions of β2-adrenoceptor agonist drug on neuromuscular function after fatigue.

The effects of β2-agonists on human skeletal muscle contractile function are unclear, more particularly in the presence of fatigue. Moreover, it remains to be ascertained whether central motor drive during voluntary contractions could counter for eventual contractile alterations induced by β2-agonists. This study explored central and peripheral neuromuscular adjustments of the quadriceps induced by β2-agonist terbutaline after fatiguing exercise. On 2 d, nine men performed 120 intermittent (5-s contraction/5-s relaxation) submaximal (50% maximal voluntary contraction [MVC]) voluntary contractions, 2 h after having ingested a terbutaline (8 mg) or placebo capsule, in a double-blind randomized order. The isometric knee extension peak torque of single twitch and tetanic (10 and 100 Hz) contractions and of MVC was recorded before (PRE) and after (POST) the fatiguing exercise. Twitch maximal rate of torque relaxation (-dT/dt) was also calculated. Central motor drive was estimated via quadriceps electromyogram recorded during the submaximal voluntary contractions. In PRE and POST conditions, MVC and twitch peak torque were not modified by terbutaline. PRE twitch -dT/dt was 22% higher in terbutaline compared with placebo (P < 0.005), but it did not differ significantly between treatments at POST. The evoked torque of 10- and 100-Hz tetanus were significantly lower in terbutaline compared with placebo, regardless of time (-16% and -17% respectively, P < 0.05). Central motor drive during voluntary exercise did not differ between treatments. These results demonstrate that terbutaline affected the contractile function of the quadriceps muscle during electrically evoked contractions both before and after fatiguing exercise. However, this did not impair the maximal voluntary force-generating capacity of the knee extensors and did not result in any compensatory adjustments of the central nervous system

M-wave, H- and V-Reflex Recruitment Curves During Maximal Voluntary Contraction

Purpose: To investigate whether the H reflex–M wave recruitment curves obtained during maximal voluntary contraction (MVC) differ from rest and to determine the stimulation intensities allowing to record stable reflex responses. Methods: Full recruitment curves (precision, 2 mA) were obtained from the soleus muscle in 14 volunteers at rest and during plantar flexion MVCs. Results: Maximal M-wave reached significantly larger amplitude during MVC (+2.2 [0.4; 3.9] mV) for a higher stimulation intensity (+7.9 [−0.4; 16] mA). Similarly, maximal H-reflex reached significantly larger amplitude during MVC than at rest (+3.2 [0.9; 5.5] mV) for a much higher stimulation intensity (+17.7 [9.7; 25.7] mA). V-wave amplitude plateaued only when M-wave during MVC plateaued, that is, at higher intensity than M-wave at rest. V-wave was correlated to the maximal H-reflex during MVC (r = 0.79, P < 0.05). Conclusion: Electrically evoked potentials showed a specific recruitment curve during MVC with higher maximal values attained for higher stimulation intensities. Thus, recording reflex responses during MVC based on intensities determined at rest or as a percentage of M-wave may yield inaccurate results. V-wave presented a plateau for stimulation intensity of 1.5 times the onset of the resting M-wave plateau. Evoked potentials obtained during actual contractions should be normalized to M-waves obtained during contractions of the same force level

Twitch and M-wave potentiation induced by intermittent maximal voluntary quadriceps contractions: Differences between direct quadriceps and femoral nerve stimulation.

Introduction: To investigate differences in twitch and M-wave potentiation in the quadriceps femoris when electrical stimulation is applied over the quadriceps muscle belly versus the femoral nerve trunk. Methods: M-waves and mechanical twitches were evoked using direct quadriceps muscle and femoral nerve stimulation between 48 successive isometric maximal voluntary contractions (MVC) from 10 young, healthy subjects. Potentiation was investigated by analyzing the changes in M-wave amplitude recorded from the vastus medialis (VM) and vastus lateralis (VL) muscles and in quadriceps peak twitch force. Results: Potentiation of twitch, VM M-wave, and VL M-wave were greater for femoral nerve than for direct quadriceps stimulation (P&lt;0.05). Despite a 50% decrease in MVC force, the amplitude of the M-waves increased significantly during exercise. Conclusions: In addition to enhanced electrogenic Na(+) -K(+) pumping, other factors (such as synchronization in activation of muscle fibers and muscle architectural properties) might significantly influence the magnitude of M-wave enlargement. © 2013 Wiley Periodicals, Inc

Spatial distribution of motor units recruited during electrical stimulation of the quadriceps muscle versus the femoral nerve.

INTRODUCTION: In this study we investigated differences in the spatial recruitment of motor units (MUs) in the quadriceps when electrical stimulation is applied over the quadriceps belly versus the femoral nerve. METHODS: M-waves and mechanical twitches were evoked using over-the-quadriceps and femoral nerve stimulation of gradually increasing intensity from 22 young, healthy subjects. Spatial recruitment was investigated using recruitment curves of M-waves recorded from the vastus medialis (VM) and vastus lateralis (VL) and of twitches recorded from the quadriceps. RESULTS: At maximal stimulation intensity (Imax), no differences were found between nerve and over-the-quadriceps stimulation. At submaximal intensities, VL M-wave amplitude was higher for over-the-quadriceps stimulation at 40% Imax, and peak twitch force was greater for nerve stimulation at 60% and 80% Imax. CONCLUSIONS: For the VM, MU spatial recruitment during nerve and over-the-quadriceps stimulation of increasing intensity occurred in a similar manner, whereas significant differences were observed for the VL. Muscle Nerve, 2013

Differences in climbing-specific strength between boulder and lead rock climbers.

Differences in climbing-specific strength between boulder and lead rock climbers. J Strength Cond Res 27(2): 310-314, 2013-The purpose of this study was to compare maximal muscle strength and rapid force capacity of finger flexors between boulder and lead climbers of national-international level. Ten boulder (mean \ub1 SD, age 27 \ub1 8 years) and 10 lead climbers (age 27 \ub1 6 years) volunteered for the study. Ten nonclimbers (age 25 \ub1 4 years) were also tested. Isometric maximal voluntary contraction (MVC) force and rate of force development (RFD) produced in "crimp" and "open-crimp" hand positions were evaluated on an instrumented hold. Climbers were stronger than nonclimbers. More interestingly, MVC force and RFD were significantly greater in boulder compared with lead climbers (p < 0.05), in both crimp and open-crimp positions. The RFD was the most discriminatory outcome, as the largest difference between boulder and lead climbers (34-38%) was observed for this variable. The RFD may reflect the specific requirements of bouldering and seems to be more appropriate than pure maximal strength for investigating muscle function in rock climbers