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Christos Papadopoulos, Vasilios I. Kalapotharakos, Georgios Noussios, Konstantinos Meliggas and Evangelia Gantiraga

Objective:

To examine the effect of static stretching on maximal voluntary contraction (MVC) and isometric force-time curve characteristics of leg extensor muscles and EMG activity of rectus femoris (RF), biceps femoris (BF), and gastrocnemius (GA).

Design:

A within subjects experimental design.

Participants:

Ten healthy students were tested after a jogging and a jogging/stretch protocol.

Intervention:

The stretching protocol involved a 10 min jog and seven static stretching exercises.

Main Outcomes:

Measurements included MVC, time achieved to MVC (TMVC), force at 100ms (F100), index of relative force (IRF), index of rate of force development (IRFD), and average integrated EMG activity (AEMG).

Results:

There were slight but no significant changes in MVC (1%), TMVC (4.8%), F100 (7.8%), IRF (1%), and IRFD (3.5%) between measurement. A significant difference (21%; P < 0.05) in AEMG of RF was found.

Conclusions:

The present study indicated that a moderate volume of static stretching did not alter significantly the MVC and the isometric force-time curve characteristics. Neural inhibition, as it is reflected from AEMG of RF, did not alter MVC and isometric force-time curve characteristics.

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Matthew S. Ganio, Jennifer F. Klau, Elaine C. Lee, Susan W. Yeargin, Brendon P. McDermott, Maxime Buyckx, Carl M. Maresh and Lawrence E. Armstrong

The purpose of this study was to compare the effects of a carbohydrate-electrolyte plus caffeine, carnitine, taurine, and B vitamins solution (CE+) and a carbohydrate-electrolyte-only solution (CE) vs. a placebo solution (PLA) on cycling performance and maximal voluntary contraction (MVC). In a randomized, double-blind, crossover, repeated-measures design, 14 male cyclists (M ± SD age 27 ± 6 yr, VO2max 60.4 ± 6.8 ml · kg−1 · min−1) cycled for 120 min submaximally (alternating 61% ± 5% and 75% ± 5% VO2max) and then completed a 15-min performance trial (PT). Participants ingested CE+, CE, or PLA before (6 ml/kg) and every 15 min during exercise (3 ml/kg). MVC was measured as a single-leg isometric extension (70° knee flexion) before (pre) and after (post) exercise. Rating of perceived exertion (RPE) was measured throughout. Total work accumulated (KJ) during PT was greater (p < .05) in CE+ (233 ± 34) than PLA (205 ± 52) but not in CE (225 ± 39) vs. PLA. MVC (N) declined (p < .001) from pre to post in PLA (988 ± 213 to 851 ± 191) and CE (970 ± 172 to 870 ± 163) but not in CE+ (953 ± 171 to 904 ± 208). At Minutes 60, 90, 105, and 120 RPE was lower in CE+ (14 ± 2, 14 ± 2, 12 ± 1, 15 ± 2) than in PLA (14 ± 2, 15 ± 2, 14 ± 2, 16 ± 2; p < .001). CE+ resulted in greater total work than PLA. CE+, but not PLA or CE, attenuated pre-to-post MVC declines. Performance increases during CE+ may have been influenced by lower RPE and greater preservation of leg strength during exercise in part as a result of the hypothesized effects of CE+ on the central nervous system and skeletal muscle.

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Lucas Ettinger, Jason Weiss, Matthew Shapiro and Andrew Karduna

In this study, we aimed to determine if electromyography (EMG) normalization to maximal voluntary isometric contractions (MVIC) was influenced by subacromial pain in patients with subacromial impingement syndrome. Patients performed MVICs in unique testing positions for each shoulder muscle tested before and after subacromial injection of local anesthetic. In addition to collection of MVIC data, EMG data during an arm elevation task were recorded before and after injection. From a visual analog pain scale, patients had a 64% decrease in pain following the injection. Significant increases in MVICs were noted in 4 of the 7 shoulder muscles tested: anterior, middle and posterior deltoid, and lower trapezius. No significant differences were noticed for the upper trapezius, latissimus dorsi, or serratus anterior. MVIC condition (pre and post injection) had a significant influence on EMG normalization for the anterior deltoid and lower trapezius muscle. Results indicate that subacromial pain can influence shoulder muscle activity, especially for the deltoid muscles and lower trapezius. In addition, normalization to MVIC in the presence of pain can have unpredictable results. Caution should be taken when normalizing EMG data to MVIC in the presence of pain.

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Daria Neyroud, Jimmy Samararatne, Bengt Kayser and Nicolas Place

intensity for femoral nerve stimulation was determined. 20 After a warm-up of 8 to 10 submaximal contractions (20–80% of estimated maximal voluntary contraction [MVC]), KE neuromuscular function was evaluated. Participants executed 2 to 3 KE MVCs for ∼4 seconds (no more than 5% variation was tolerated

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Thomas Cattagni, Clément Billet, Christophe Cornu and Marc Jubeau

Context: Prolonged tendon vibration may induce muscle fatigue, as assessed by a decrease in maximal force production. It remains unknown, however, whether the decrease in muscle strength after prolonged Achilles tendon vibration is related to the vibration frequency. Objective: To assess the maximal capacity of plantar-flexor (PF) neuromuscular function before and after prolonged Achilles tendon vibration at low and high frequencies generated using a portable device. Design: Pre- and posttest intervention with control.Setting: University laboratory. Participants: 10 healthy men age 22.6 ± 4.0 y. Intervention: Each subject participated in 3 experimental sessions that were randomly distributed and separated by 1 wk. During each experimental session, 1 of the following vibration protocols was applied for 30 min: 40-Hz vibration, 100-Hz vibration, or no vibration (control protocol). Main Outcome Measures: Maximal-voluntary-contraction torque, voluntary activation level, twitch torque, maximal electromyographic activity, and maximal M-wave of PF muscles (measured before and after each vibration or control protocol).Results: Statistical analysis exhibited no significant effect of vibration protocol on the measured variables. Conclusions: The current study demonstrates that 30 min of Achilles tendon vibration at a low or high frequency using a portable stimulator did not affect the neuromuscular performance of the PF muscles. These results emphasize the limits of tendon vibration, whatever the frequency applied, for inducing neuromuscular fatigue.

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Stephen P. Bailey, Julie Hibbard, Darrin La Forge, Madison Mitchell, Bart Roelands, G. Keith Harris and Stephen Folger

Background: Carbohydrate (CHO) mouth rinse (MR) before exercise has been shown to improve physical performance and corticospinal motor excitability. Purpose: To determine the effects of different forms of CHO MR on quadriceps muscle performance and corticospinal motor excitability. Methods: 10 subjects (5 female and 5 male; 25 [1] y, 1.71 [0.03] m, 73 [5] kg) completed 4 conditions (placebo [PLA], 6.4% glucose [GLU], 6.4% maltose [MAL], 6.4% maltodextrin [MDX]). Maximal voluntary contraction (MVIC) of the right quadriceps and motor-evoked potential (MEP) of the right rectus femoris was determined pre (10 min), immediately after, and post (10 min) 20-s MR. MEP was precipitated by transcranial magnetic stimulation during muscle contraction (50% MVIC). Results: The relative change in MEP from pre-measures was different across treatments (P = .025) but was not different across time (P = .357). MEP was greater for all CHO conditions immediately after (GLU = 2.58% [5.33%], MAL = 3.92% [3.90%], MDX = 18.28% [5.57%]) and 10 min after (GLU = 14.09% [13.96%], MAL = 8.64% [8.67%], MDX = 31.54% [12.77%]) MR than PLA (immediately after = −2.19% [4.25%], 10 min = −13.41% [7.46%]). MVC was greater for CHO conditions immediately (GLU = 3.98% [2.49%], MAL = 5.89% [2.29%], MDX = 7.66% [1.93%]) and 10 min after (GLU = 7.22% [2.77%], MAL = 10.26% [4.22%], MDX = 10.18% [1.50%]) MR than PLA (immediately after = −3.24% [1.50%], 10 min = −6.46% [2.22%]). Conclusions: CHO MR increased corticospinal motor excitability and quadriceps muscle after application. The form of CHO used did not influence this response.

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Lewis J. Macgregor, Massimiliano Ditroilo, Iain J. Smith, Malcolm M. Fairweather and Angus M. Hunter

Context:

Assessments of skeletal-muscle functional capacity often necessitate maximal contractile effort, which exacerbates muscle fatigue or injury. Tensiomyography (TMG) has been investigated as a means to assess muscle contractile function after fatigue; however, observations have not been contextualized by concurrent physiological measures.

Objective:

To measure peripheral-fatigue-induced alterations in mechanical and contractile properties of the plantar-flexor muscles through noninvasive TMG concurrently with maximal voluntary contraction (MVC) and passive muscle tension (PMT) to validate TMG as a gauge of peripheral fatigue.

Design:

Pre- and posttest intervention with control.

Setting:

University laboratory.

Participants:

21 healthy male volunteers.

Interventions:

Subjects’ plantar flexors were tested for TMG parameters, along with MVC and PMT, before and after either a 5-min rest period (control) or a 5-min electrical-stimulation intervention (fatigue).

Main Outcome Measures:

Temporal (contraction velocity) and spatial (radial displacement) contractile parameters of the gastrocnemius medialis were recorded through TMG. MVC was measured as an indicator of muscle fatigue, and PMT was measured to assess muscle stiffness.

Results:

Radial displacement demonstrated a fatigue-associated reduction (3.3 ± 1.2 vs 4.0 ± 1.4 mm, P = .031), while contraction velocity remained unaltered. In addition, MVC significantly declined by 122.6 ± 104 N (P < .001) after stimulation (fatigue). PMT was significantly increased after fatigue (139.8 ± 54.3 vs 111.3 ± 44.6 N, P = .007).

Conclusions:

TMG successfully detected fatigue, evident from reduced MVC, by displaying impaired muscle displacement accompanied by elevated PMT. TMG could be useful in establishing skeletalmuscle fatigue status without exacerbating the functional decrement of the muscle.

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Tyler W.D. Muddle, David H. Fukuda, Ran Wang, Joshua J. Riffe, David D. Church, Kyle S. Beyer, Jay R. Hoffman and Jeffrey R. Stout

measurements (SEMs) for the A-mode ultrasound were assessed as 0.949 (SEM: 2.04%). Assessment of Bilateral Reactionary Gripping Task Maximal voluntary contraction familiarization Following the completion of all questionnaires and body composition measurements, participants who met the study criteria were

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Eduardo Lusa Cadore, Miriam González-Izal, Rafael Grazioli, Igor Setuain, Ronei Silveira Pinto and Mikel Izquierdo

after. Echo intensity was assessed before and 48 hours after protocols. MVC indicates maximal voluntary contraction. Participants A total of 22 physically active participants (14 females and 8 males), who were engaged recreationally in different sports modalities, participated in the study and were

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Garrett M. Hester, Zachary K. Pope, Mitchel A. Magrini, Ryan J. Colquhoun, Alejandra Barrera-Curiel, Carlos A. Estrada, Alex A. Olmos and Jason M. DeFreitas

. Consistent verbal encouragement and visual biofeedback were provided during each session. Testing Protocol Maximal voluntary contractions for the knee extensors of both legs were performed using the isokinetic dynamometer at the highest isokinetic velocity setting (500 deg/s). Prior to testing, subjects