Jared W. Coburn

The acute effects of static stretching on peak torque, mean power output, electromyography, and mechanomyography

The purpose of this study was to examine the acute effects of static stretching on peak torque (PT), the joint angle at PT, mean power output (MP), electromyographic (EMG) amplitude, and mechanomyographic (MMG) amplitude of the vastus lateralis (VL) and rectus femoris (RF) muscles during maximal, voluntary concentric isokinetic leg extensions at 60 and 240°·s-1 of the stretched and unstretched limbs. Twenty-one volunteers [mean age (SD) 21.5 (1.3)xa0years] performed maximal, voluntary concentric isokinetic leg extensions for the dominant and non-dominant limbs at 60 and 240°·s-1. Surface EMG (μVrms) and MMG (mVrms) signals were recorded from the VL and RF muscles during the isokinetic tests. PT (Nm), the joint angle at PT, and MP (W) were calculated by a dynamometer. Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. PT decreased (P≤0.05) from pre- to post-stretching for the stretched limb at 60 and 240°·s-1 and for the unstretched limb at 60°·s-1. EMG amplitude of the VL and RF also decreased (P≤0.05) from pre- to post-stretching for the stretched and unstretched limbs. There were no stretching-induced changes (P>0.05) for the joint angle at PT, MP, or MMG amplitude. These findings indicated stretching-induced decreases in force production and muscle activation. The decreases in PT and EMG amplitude for the unstretched limb suggested that the stretching-induced decreases may be due to a central nervous system inhibitory mechanism.

The acute effects of a caffeine-containing supplement on strength, muscular endurance, and anaerobic capabilities.

The purpose of this study was to examine the acute effects of a caffeine-containing supplement on upper-and lower-body strength and muscular endurance as well as anaerobic capabilities. Thirty-seven resistance-trained men (mean ± SD, age: 21 ± 2 years) volunteered to participate in this study. On the first laboratory visit, the subjects performed 2 Wingate Anaerobic Tests (WAnTs) to determine peak power (PP) and mean power (MP), as well as tests for 1 repetition maximum (1RM), dynamic constant external resistance strength, and muscular endurance (TOTV; total volume of weight lifted during an endurance test with 80% of the 1RM) on the bilateral leg extension (LE) and free-weight bench press (BP) exercises. Following a minimum of 48 hours of rest, the subjects returned to the laboratory for the second testing session and were randomly assigned to 1 of 2 groups: a supplement group (SUPP; n = 17), which ingested a caffeine-containing supplement, or a placebo group (PLAC; n = 20), which ingested a cellulose placebo. One hour after ingesting either the caffeine-containing supplement or the placebo, the subjects performed 2 WAnTs and were tested for 1RM strength and muscular endurance on the LE and BP exercises. The results indicated that there was a significant (p < 0.05) increase in BP 1RM for the SUPP group, but not for the PLAC group. The caffeine-containing supplement had no effect, however, on LE 1RM, LE TOTV, BP TOTV, PP, and MP. Thus, the caffeine-containing supplement may be an effective supplement for increasing upper-body strength and, therefore, could be useful for competitive and recreational athletes who perform resistance training.

Mechanomyographic and Electromyographic Responses of the Vastus Medialis Muscle During Isometric and Concentric Muscle Actions

The purpose of this study was to examine the patterns for the mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) vs. torque relationships during submaximal to maximal isometric and isokinetic muscle actions. Seven men (mean ± SD age, 22.4 ± 1.3 years) volunteered to perform isometric and concentric isokinetic leg extension muscle actions at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC) and peak torque (PT) on a Cybex II dynamometer. A piezoelectric MMG recording sensor was placed between bipolar surface EMG electrodes on the vastus medialis. Polynomial regression and separate 1-way repeated-measures analysis of variance were used to analyze the EMG amplitude, MMG amplitude, EMG MPF, and MMG MPF data for the isometric and isokinetic muscle actions. For the isometric muscle actions, EMG amplitude (R2 = 0.999) and MMG MPF (R2 = 0.946) increased to MVC, mean MMG amplitude increased to 60% MVC and then plateaued, and mean EMG MPF did not change (p > 0.05) across torque levels. For the isokinetic muscle actions, EMG amplitude (R2 = 0.988) and MMG amplitude (R2 = 0.933) increased to PT, but there were no significant mean changes with torque for EMG MPF or MMG MPF. The different torque-related responses for EMG and MMG amplitude and MPF may reflect differences in the motor control strategies that modulate torque production for isometric vs. dynamic muscle actions. These results support the findings of others and suggest that isometric torque production was modulated by a combination of recruitment and firing rate, whereas dynamic torque production was modulated primarily through recruitment.

Mechanomyographic and electromyographic time and frequency domain responses during submaximal to maximal isokinetic muscle actions of the biceps brachii.

The purpose of this investigation was to determine the mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) versus torque relationships during isokinetic muscle actions of the biceps brachii. Twelve adults [meanxa0(SD) age, 22.2xa0(2.7)xa0years] performed submaximal to maximal isokinetic muscle actions of the dominant forearm flexors. Following determination of isokinetic peak torque (PT), the subjects randomly performed submaximal muscle actions in 20% increments from 20% to 80% PT. Polynomial regression analyses indicated linear increases in both MMG (r2=0.984) and EMG (r2=0.988) amplitude to 100% PT. There were no significant (P>0.05) relationships, however, for MMG and EMG MPF versus isokinetic torque. The results demonstrated similar responses for MMG and EMG in both the time and frequency domains. These findings suggested that simultaneous examination of MMG and EMG amplitude and MPF may be useful for describing the unique motor control strategies that modulate dynamic torque production. Furthermore, the results indicated that dynamic muscle actions can be used when applying techniques that require a linear EMG amplitude versus torque relationship.

The effects of interelectrode distance on electromyographic amplitude and mean power frequency during incremental cycle ergometry.

The purpose of this study was to examine the effects of interelectrode distance (IED) on the relationships of absolute and normalized EMG amplitude and mean power frequency (MPF) versus power output during incremental cycle ergometry. Eleven adults (mean +/- S.D. age = 24.2 +/- 2.6 y; V(O2max) = 49.4 +/- 8.3 ml kg(-1) min(-1)) performed incremental cycle ergometry tests. Surface EMG signals were recorded simultaneously from bipolar electrode arrangements placed over the VL muscle with IEDs of 20, 40, and 60 mm. Polynomial regression analyses were used to describe the relationships for absolute and normalized EMG amplitude (muV(rms) and % max) and MPF (Hz and % max) versus power output (%max) for each subject at the three IEDs. In addition, separate one-way repeated measures ANOVAs were used to examine mean differences between the three IEDs for absolute and normalized EMG amplitude and MPF at power outputs of 80, 110, 140, and 170 W. The results of the polynomial regression revealed that the best fit model for each IED for the absolute and normalized EMG amplitude was linear for six of the 11 subjects and quadratic for five of the subjects. For EMG MPF, four of the 11 subjects exhibited significant relationships (linear or quadratic) across power outputs for at least one IED. The one-way repeated measures ANOVAs revealed significant mean differences between the IEDs for absolute EMG amplitude and MPF at 80, 110, 140, and 170 W. There were no significant mean differences, however, between the IEDs for normalized EMG amplitude or MPF at 80, 110, 140, and 170 W. The results of the study indicated that there were no consistent patterns of responses between individual subjects for EMG amplitude or MPF versus power output relationships for IEDs of 20, 40, and 60 mm during incremental cycle ergometry. The current findings supported the process of normalization for EMG amplitude and MPF data obtained during cycle ergometry when comparisons are made for different IEDs.

Effects of a drink containing creatine, amino acids, and protein combined with ten weeks of resistance training on body composition, strength, and anaerobic performance.

The purpose of this study was to examine the effects of a drink containing creatine, amino acids, and protein vs. a carbohydrate placebo on body composition, strength, muscular endurance, and anaerobic performance before and after 10 weeks of resistance training. Fifty-one men (mean ± SD; age: 21.8 ± 2.9 years) were randomly assigned to either the test drink (TEST; n = 23) or the placebo (PLAC; n = 28) and performed two 30-second Win-gate Anaerobic Tests for determination of peak power (PP) and mean power (MP), were weighed underwater for percent body fat (%fat) and fat-free mass (FFM), and were tested for 1 repetition maximum (1RM) dynamic constant external resistance strength and muscular endurance (END; number of repetitions performed with 80% of 1RM) on the bilateral leg extension (LE) and free-weight bench press (BP) exercises. The testing was conducted before (PRE) and after (POST) 10 weeks of resistance training (3 sets of 10 repetitions with 80% of the subjects 1RM performed 3 times per week) on the LE and BP exercises. Body weight, FFM, LE 1RM, LE END, BP 1RM, and BP END increased (p < 0.05), whereas %fat decreased (p < 0.05) from PRE to POST for both the TEST and PLAC groups. Peak power and MP, however, increased for the TEST group, but not for the PLAC group. These results suggested that the creatine-, amino acid–, and protein-containing drink provided no additional benefits when compared with carbohydrates alone for eliciting changes in body composition, strength, and muscular endurance after a 10-week resistance training period. The TEST drink was, however, more effective than carbohydrates alone for improving anaerobic power production.

Validity of VO2max Equations for Aerobically Trained Males and Females

PURPOSEnThe purpose of this investigation was to cross-validate existing VO2max prediction equations on samples of aerobically trained males and females.nnnMETHODSnA total of 142 aerobically trained males (mean +/- SD; 39.0 +/- 11.1 yr, N = 93) and females (39.7 +/- 10.1 yr, N = 49) performed a maximal incremental test to determine actual VO2max on a cycle ergometer. The predicted VO2max values from 18 equations (nine for each gender) were compared with actual VO2max by examining the constant error (CE), standard error of estimate (SEE), correlation coefficient (r), and total error (TE).nnnRESULTSnThe results of this investigation indicated that all of the equations resulted in significant (P < 0.006) CE values ranging from -216 to 1415 mL x min(-1) for the males and 132 to 1037 mL x min(-1) for the females. In addition the SEE, r, and TE values ranged from 266 to 609 mL x min(-1), 0.36 to 0.88, and 317 to 1535 mL x min(-1), respectively. Furthermore, the lowest TE values for the males and females represented 10% and 12% of the mean actual VO2max values, respectively.nnnCONCLUSIONSnThe results of the analysis indicated that the two equations using age, body weight, and the power output achieved at VO2 as predictor variables had the lowest SEE (7.7-9.8% of actual VO2max) and TE (10-12% of actual VO2max) values and are recommended for estimating VO2max in aerobically trained males and females. The magnitude of the TE values (>or= 20% of actual VO2max) associated with the remaining 16 equations, however, were too large to be of practical value for estimating VO2max.

A new non-exercise-based Vo2max prediction equation for aerobically trained men.

The purposes of the present study were to (a) modify previously published VO2max equations using the constant error (CE = mean difference between actual and predicted VO2max) values from Malek et al. (28); (b) cross-validate the modified equations to determine their accuracy for estimating VO2max in aerobically trained men; (c) derive a new non–exercise-based equation for estimating VO2max in aerobically trained men if the modified equations are not found to be accurate; and (d) cross-validate the new VO2max equation using the predicted residual sum of squares (PRESS) statistic and an independent sample of aerobically trained men. One hundred and fifty-two aerobically trained men (VO2max mean ± SD = 4,154 ± 629 ml·min-1) performed a maximal incremental test on a cycle ergometer to determine actual VO2max. An aerobically trained man was defined as someone who had participated in continuous aerobic exercise 3 or more sessions per week for a minimum of 1 hour per session for at least the past 18 months. Nine previously published VO2max equations were modified for use with aerobically trained men. The predicted VO2max values from the 9 modified equations were compared to actual VO2max by examining the CE, standard error of estimate (SEE), validity coefficient (r), and total error (TE). Cross-validation of the modified non–exercise-based equations on a random subsample of 50 subjects resulted in a %TE ≥ 13% of the mean of actual VO2max. Therefore, the following non-exercise-based VO2max equation was derived from a random subsample of 112 subjects: VO2max (ml·min-1) = 27.387(weight in kg) + 26.634(height in cm) - 27.572(age in years) + 26.161(h·wk-1 of training) + 114.904(intensity of training using the Borg 6-20 scale) + 506.752(natural log of years of training) - 4,609.791 (R = 0.82, R2 adjusted = 0.65, and SEE = 378 ml·min-1). Cross-validation of this equation on the remaining sample of 40 subjects resulted in a %TE of 10%. Therefore, the non-exercise-based equation derived in the present study is recommended for estimating VO2max in aerobically trained men.

A New Nonexercise-based VO2(max) Equation for Aerobically Trained Females

PURPOSEnThe purposes of the present study were to (a) modify previously published VO2(max) equations using the constant error (CE) values for aerobically trained females, (b) cross-validate the modified equations to determine their accuracy for estimating VO2(max) in aerobically trained females, (c) derive a new nonexercise-based equation for estimating VO2(max) in aerobically trained females if the modified equations are found to be inaccurate, and (d) cross-validate the new VO2(max) equation using the PRESS statistic and an independent sample of aerobically trained females.nnnMETHODSnA total of 115 aerobically trained females (mean +/- SD: age = 38.5 +/- 9.4 yr) performed a maximal incremental test on a cycle ergometer to determine actual VO2(max). The predicted VO2(max) values from nine published equations were compared with actual VO2(max) by examining the CE, standard error of estimate (SEE), validity coefficient (r), and total error (TE).nnnRESULTSnCross-validation of the modified nonexercise-based equations on a random subsample of 50 subjects resulted in a %TE > or = 13% of the mean of actual VO2(max). Therefore, the following nonexercise-based VO2(max) equation was derived on a random subsample of 80 subjects: VO2(max) (mL x min(-1)) = 18.528 (weight in kg) + 11.993 (height in cm) - 17.197(age in yr) + 23.522 (h x wk(-1) of training) + 62.118 (intensity of training using the Borg 6-20) + 278.262 (natural log of years of training) - 1375.878 (R = 0.83, R2 adjusted = 0.67, and SEE = 259 mL x min(-1)). Cross-validation of this equation on the remaining sample of 35 subjects resulted in a %TE of 10%.nnnCONCLUSIONSnThe nonexercise equation presented here is recommended over previously published equations for estimating VO2(max) in aerobically trained females.

Mechanomyographic and Electromyographic Responses During Submaximal to Maximal Eccentric Isokinetic Muscle Actions of the Biceps Brachii

The purpose of this investigation was to determine the mechanomyography (MMG) and electromyography (EMG) amplitude and mean power frequency (MPF) vs. eccentric isokinetic torque relationships for the biceps brachii muscle. Nine adults (mean ± SD age = 23.1 ± 2.9 years) performed submaximal to maximal eccentric iso-kinetic muscle actions of the dominant forearm flexors. After determination of isokinetic peak torque (PT), the subjects randomly performed submaximal step muscle actions in 10% increments from 10 to 90% PT. Polynomial regression analyses indicated that the MMG amplitude vs. eccentric isokinetic torque relationship was best fit with a quadratic model (R2 = 0.951), where MMG amplitude increased from 10 to 60% PT and then plateaued from 60 to 100% PT. There were linear increases in MMG MPF (r2 = 0.751) and EMG amplitude (r2 = 0.988) with increases in eccentric isokinetic torque, but there was no significant change in EMG MPF from 10 to 100% PT. The results suggested that for the biceps brachii, eccentric isokinetic torque was increased to approximately 60% PT through concurrent modulation of the number of active motor units and their firing rates, whereas additional torque above 60% PT was produced only by increases in firing rates. These findings contribute to current knowledge of motor-control strategies during eccentric isokinetic muscle actions and could be useful in the design of training programs.