Effects of Dynamic Stretching on Strength, Muscle Imbalance, and Muscle Activation

Purpose: This study aimed to examine the acute effects of dynamic stretching on concentric leg extensor and flexor peak torque, eccentric leg flexor peak torque, and the conventional and functional hamstring–quadriceps (H:Q) ratios. Methods: Twenty-one women (mean ± SD age = 20.6 ± 2.0 yr, body mass = 64.5 ± \u3e.3 kg, height = 164.7 ± 6.5 cm) performed maximal voluntary isokinetic leg extension, flexion, and eccentric hamstring muscle actions at the angular velocities of 60°· s-1 and 180° · s-1 before and after a bout of dynamic hamstring and quadriceps stretching as well as a control condition. Results: Leg flexion peak torque decreased under both control (mean ± SE for 60°· s-1 = 75.8 ± 4.0 to 72.4 ± 3.7 N · m, 180° · s-1 = 62.1 ± 3.2 to 59.1 ± 3.1 N· m) and stretching (60°· s-1 = 73.1 ± 3.\u3e to 65.8 ± 3.3 N· m, 180°· s-1 = 61.2 ± 3.3 to 54.7 ± 2.6 N· m) conditions, whereas eccentric hamstring peak torque decreased only after the stretching (60°· s-1 = 87.3 ± 5.1 to 73.3 ± 3.6 N· m, 180°· s-1 = 89.2 ± 4.4 to 77.0 ± 3.4 N · m) intervention (P ≤ 0.05). Stretching also caused a decrease in conventional H:Q (60°· s-1 = 0.58 ± 0.02 to 0.54 ± 0.02, 180°· s-1 = 0.67 ± 0.02 to 0.61 ± 0.03) and functional H:Q ratios (60°· s-1 = 0.69 ± 0.03 to 0.60 ± 0.03, 180°· s-1 = 1.00 ± 0.06 to 0.60 ± 0.03) (P ≤ 0.05). Conclusions: Because dynamic stretching reduced concentric and eccentric hamstring strength as well as the conventional and functional H:Q ratios, fitness and allied-health professionals may need to be cautious when recommending dynamic rather than static stretching to maintain muscle force

Effects of a supplement designed to increase ATP levels on muscle strength, power output, and endurance

<p>Abstract</p> <p>Background</p> <p>The present study examined the acute effects of a nutritional supplement intended to improve adenosine triphosphate (ATP) concentrations on vertical jump height, isometric strength of the leg extensors, leg extension endurance, and forearm flexion endurance.</p> <p>Methods</p> <p>Twenty-four healthy men (mean age ± SD = 23 ± 4 yrs, stature = 181 ± 7 cm, and body mass = 82 ± 12 kg) volunteered to complete a familiarization trial plus 2 randomly-ordered experimental trials separated by a 7-day washout period. Participants received either 6 (body mass < 91 kg) or 8 (body mass ≥ 91 kg) tablets of the treatment (TR; 625 mg of adenylpyrophosphoric acid and calcium pyruvate, 350.8 mg of cordyceps sinensis extract and yohimbine hydrochloride) or placebo (PL; 980 mg of microcrystalline cellulose) 1 hour prior to the following tests: countermovement vertical jump (CVJ), forearm flexion repetitions to exhaustion, isometric maximal voluntary contractions (MVCs) of the leg extensors, and a 50-repetition maximal concentric isokinetic leg extension endurance test.</p> <p>Results</p> <p>There were no differences between the TR and PL trials for CVJ height (<it>P </it>> 0.05), isometric MVC peak torque (<it>P </it>> 0.05), maximal concentric isokinetic peak torque (<it>P </it>> 0.05), percent decline during the leg extension endurance tests (<it>P </it>> 0.05), or repetitions to exhaustion during the forearm flexion endurance tests (<it>P </it>> 0.05).</p> <p>Conclusion</p> <p>These findings indicated no improvements in the measured variables as a result of ingesting this nutritional supplement. Future studies should examine whether chronic supplementation or a loading period is necessary to observe any ergogenic effects of this supplement.</p

Exertional rhabdomyolysis in a 21-year-old, healthy female after performing three sets of the biceps curl exercise to failure with 30% 1RM: A case report

Background: The optimal resistance training program to elicit muscle hypertrophy has been consistently debated and researched. Although 3 sets of 10 repetitions at 70-80% of the 1-repetition maximum (1RM) is widely recommended, recent studies have shown that low-load (~30% 1RM), high-repetition (3 sets of 30-40 repetitions) resistance training can elicit similar muscular hypertrophy. Therefore, this type of resistance training has gained popularity, perhaps because less weight is lifted for a longer duration. In the process of testing this hypothesis in a research study in our laboratory, a subject diagnosed with exertional rhabdomyolysis after completing a single resistance training session that involved 3 sets to failure at 30% 1RM. Exertional rhabdomyolysis is a condition characterized by the excessive breakdown of striated skeletal muscle that releases proteins from the muscle cell, particularly myoglobin, into the blood that can be toxic to the kidneys and is a significant health concern. Case Report: Reviewed were the events leading up to and throughout the diagnosis of exertional rhabdomyolysis in a healthy, recreationally-trained, 21-year-old female that was enrolled in a study that compared the acute effects of the traditional high-load, low-repetition versus low-load, high-repetition resistance training. The subject completed a total of 143 repetitions of the bilateral dumbbell bicep curl exercise. Three days post-exercise she reported excessive muscle soreness and swelling and sought medical attention. She was briefly hospitalized and then discharged with instructions to take acetaminophen for soreness, drink plenty of water, rest, and monitor her creatine kinase (CK) concentrations. Changes in the subject’s CK concentrations, ultrasound-determined muscle thickness and echo intensity were monitored over a 14-day period are reported. Discussion: This case illustrates the potential risk of developing exertional rhabdomyolysis after a low-load, high-repetition resistance training session in healthy, young, recreationally-trained women. The fact that exertional rhabdomyolysis is a possible outcome is enough to warrant caution when prescribing this type of resistance exercise

Spin transport in multilayer systems with fully epitaxial NiO thin films

We report the generation and transport of thermal spin currents in fully epitaxial γ−Fe2O3/NiO(001)/Pt and Fe3O4/NiO(001)/Pt trilayers. A thermal gradient, perpendicular to the plane of the sample, generates a magnonic spin current in the ferrimagnetic maghemite (γ−Fe2O3) and magnetite (Fe3O4) thin films by means of the spin Seebeck effect. The spin current propagates across the epitaxial, antiferromagnetic insulating NiO layer, before being detected in the Pt layer by the inverse spin Hall effect. The transport of the spin signal is studied as a function of the NiO thickness, temperature, and ferrimagnetic material where the spin current is generated. In epitaxial NiO grown on maghemite, the spin Seebeck signal decays exponentially as a function of the NiO thickness, with a spin-diffusion length for thermally generated magnons of λMSDL=1.6±0.2nm (where MSDL is mean spin-diffusion length), largely independent of temperature. We see no enhancement of the spin-current signal as previously reported for certain temperatures and thicknesses of the NiO. In epitaxial NiO grown on magnetite, the temperature-averaged spin-diffusion length is λMSDL=3.8±0.3nm, and we observe an enhancement of the spin signal when the NiO thickness is 0.8 nm, demonstrating that the growth conditions dramatically affect the spin-transport properties of the NiO even for full epitaxial growth. In contrast to theoretical predictions for coherent spin transport, we do not see vastly different spin-diffusion lengths between epitaxial and polycrystalline NiO layers

Endogenous versus exogenous carbohydrate oxidation measured by stable isotopes in pre-pubescent children plus 13C abundances in foods consumed three days prior

Purpose: The purposes of the present study were to (a) examine resting metabolism, substrate utilization, and endogenous versus exogenous carbohydrate (CHO) oxidation before and after 30-g rapidly-digesting carbohydrate (RDC) ingestion using indirect calorimetry and breath test analysis of stable isotope concentrations in pre-pubescent children and (b) report the 13C abundances in foods consumed for three days prior. Methods: Nineteen children (n 1⁄4 10 boys, n 1⁄4 9 girls) at Tanner stage I or II participated (mean age ± 95% CI 1⁄4 9.84 ± 0.77 y) in this study. Food was administered to the children for three days preceding their scheduled breath tests. Breath tests and indirect calorimetry were performed after an 8-h fast before and 60 min following consumption of a 30-g simple RDC drink consisting of maltodextrin and sucrose. Open circuit spirometry and indirect calorimetry monitored resting metabolism and CHO oxidation. Separate breath samples were taken every 15 min. Samples of all foods and breath samples were analyzed for 13C and 12C abundances with a stable-isotope mass spectrometer. Results: 13C in expired breath samples were 23.81 + 1.64‰ at baseline and increased every 15 min after consumption of the CHO drink (p \u3c 0.001e0.009). Cumulative total, endogenous, and exogenous CHO utilization increased during the post-prandial period (p \u3c 0.001). Endogenous CHO oxidation was consistently greater than exogenous CHO oxidation (p \u3c 0.001e0.002). Blood glucose was elevated from baseline at 30- and 60-min post-prandial (p \u3c 0.001). Insulin did not change over time (p 1⁄4 0.184). Conclusions: The foods provided during the 3-day controlled diet effectively minimized 13C variation prior to metabolic testing. The 13C abundances of foods reported herein should serve as practical recommendations to reduce 13C intake before breath tests. While endogenous CHO oxidation remained greater in proportion to exogenous CHO oxidation, these findings suggest that even a relatively small amount of RDC can increase exogenous CHO oxidation and blood glucose in normal-weight children. To further examine shifts in endogenous versus exogenous CHO utilization, we recommend that future studies take steps to minimize 13C variation before breath tests and examine changes in substrate metabolism at rest and during exercise in normal weight and overweight pre-pubescent children. Clinical trial registration number: NCT03185884

Effects of creatine loading on electromyographic fatigue threshold during cycle ergometry in college-aged women

This is the publisher's version, also found at http://www.jissn.com/content/4/1/20The purpose of this study was to examine the effects of 5 days of Creatine (Cr) loading on the electromyographic fatigue threshold (EMGFT) in college-aged women. Fifteen healthy college-aged women (mean ± SD = 22.3 ± 1.7 yrs) volunteered to participate in this double-blind, placebocontrolled study and were randomly placed into either placebo (PL – 10 g of flavored dextrose powder; n = 8) or creatine (Cr – 5 g di-creatine citrate plus 10 g of flavored dextrose powder; n = 7; Creatine Edge, FSI Nutrition) loading groups. Each group ingested one packet 4 times per day (total of 20 g/day) for 5 days. Prior to and following supplementation, each subject performed a discontinuous incremental cycle ergometer test to determine their EMGFT value, using bipolar surface electrodes placed on the longitudinal axis of the right vastus lateralis. Subjects completed a total of four, 60 second work bouts (ranging from 100–350 W). The EMG amplitude was averaged over 10 second intervals and plotted over the 60 second work bout. The resulting slopes from each successive work bouts were used to calculate EMGFT. A two-way ANOVA (group [Cr vs. PL] × time [pre vs. post]) resulted in a significant (p = 0.031) interaction. Furthermore, a dependent samples t-test showed a 14.5% ± 3.5% increase in EMGFT from pre- to post-supplementation with Cr (p = 0.009), but no change for the PL treatment (-2.2 ± 5.8%; p = 0.732). In addition, a significant increase (1.0 ± 0.34 kg; p = 0.049) in weight (kg) was observed in the Cr group but no change for PL (-0.2 kg ± 0.2 kg). These findings suggest that 5 days of Cr loading in women may be an effective strategy for delaying the onset of neuromuscular fatigue during cycle ergometry

Gender Comparisons of Mechanomyographic Amplitude and Mean Power Frequency Versus Isometric Torque Relationships

This is the publisher's version, also found at http://ehis.ebscohost.com/ehost/detail?sid=e7a03093-e666-4634-b895-d6b4313857c2%40sessionmgr13&vid=1&hid=17&bdata=JnNpdGU9ZWhvc3QtbGl2ZQ%3d%3d#db=s3h&AN=15943883This study compared the patterns of mechanomyographic (MMG) amplitude and mean power frequency vs. torque relationships in men and women during isometric muscle actions of the biceps brachii. Seven men (mean age 23.9 ± 3.5 yrs) and 8 women (mean 21.0 ± 1.3 yrs) performed submaximal to maximal isometric muscle actions of the dominant forearm flexors. Following determination of the isometric maximum voluntary contraction (MVC), they randomly performed submaximal step muscle actions in 10% increments from 10% to 90% MVC. Polynomial regression analyses indicated that the MMG amplitude vs. isometric torque relationship for the men was best fit with a cubic model (R2 = 0.983), where MMG amplitude increased slightly from 10% to 20% MVC, increased rapidly from 20% to 80% MVC, and plateaued from 80% to 100% MVC. For the women, MMG amplitude increased linearly (r2 = 0.949) from 10% to 100% MVC. Linear models also provided the best fit for the MMG mean power frequency vs. isometric torque relationship in both the men (r2 = 0.813) and women (r2 = 0.578). The results demonstrated gender differences in the MMG amplitude vs. isometric torque relationship, but similar torque-related patterns for MMG mean power frequency. These findings suggested that the plateau in MMG amplitude at high levels of isometric torque production for the biceps brachii in the men, but not the women, may have been due to greater isometric torque, muscle stiffness, and/or intramuscular fluid pressure in the men, rather than to differences in moto

Effect of sex on torque, recovery, EMG, and MMG responses to fatigue

The purpose of the present investigation was to examine the effect of sex on maximal voluntary isometric contraction (MVIC) torque and the EMG and MMG responses as a result of fatiguing, intermittent, submaximal (65% of MVIC), isometric elbow flexion muscle contractions. Methods: Eighteen men and women performed MVIC trials before (pretest), after (posttest), and 5-min after (5-min recovery) performing 50 intermittent, submaximal isometric muscle contractions. Surface electromyographic (EMG) and mechanomyographic (MMG) signals were simultaneously recorded from the biceps brachii muscle. Results: As a result of the fatiguing workbout torque decreased similarly from pretest to posttest for both the men (24.0%) and women (23.3%). After 5-min of recovery, torque had partially recovered for the men, while torque had returned to pretest levels for the women. For both sexes, from pretest to posttest EMG mean power frequency and MMG amplitude decreased, but returned to pretest levels after 5-min of recovery. Conclusions: In the present study, there were sex-related differences in muscle fatigue that were not associated with the EMG or MMG responses

Effect of sex on torque, recovery, EMG, and MMG responses to fatigue

The purpose of the present investigation was to examine the effect of sex on maximal voluntary isometric contraction (MVIC) torque and the EMG and MMG responses as a result of fatiguing, intermittent, submaximal (65% of MVIC), isometric elbow flexion muscle contractions. Methods: Eighteen men and women performed MVIC trials before (pretest), after (posttest), and 5-min after (5-min recovery) performing 50 intermittent, submaximal isometric muscle contractions. Surface electromyographic (EMG) and mechanomyographic (MMG) signals were simultaneously recorded from the biceps brachii muscle. Results: As a result of the fatiguing workbout torque decreased similarly from pretest to posttest for both the men (24.0%) and women (23.3%). After 5-min of recovery, torque had partially recovered for the men, while torque had returned to pretest levels for the women. For both sexes, from pretest to posttest EMG mean power frequency and MMG amplitude decreased, but returned to pretest levels after 5-min of recovery. Conclusions: In the present study, there were sex-related differences in muscle fatigue that were not associated with the EMG or MMG responses