OBJECTIVE: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.

OBJECTIVE:To determine the effects of constant versus alternating applications of torque during fatiguing, intermittent isometric muscle actions of the leg extensors on maximal voluntary isometric contraction (MVIC) torque and neuromuscular responses.METHODS:Sixteen subjects performed two protocols, each consisting of 50 intermittent isometric muscle actions of the leg extensors with equal average load at a constant 60% MVIC or alternating 40 then 80% (40/80%) MVIC with a work-to-rest ratio of 6-s on and 2-s off. MVIC torque as well as electromyographic signals from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) and mechanomyographic signals from the VL were recorded pretest, immediately posttest, and 5-min posttest.RESULTS:The results indicated that there were no time-related differences between the 60% MVIC and 40/80% MVIC protocols. The MVIC torque decreased posttest (22 to 26%) and remained depressed 5-min posttest (9%). There were decreases in electromyographic frequency (14 to 19%) and mechanomyographic frequency (23 to 24%) posttest that returned to pretest levels 5-min posttest. There were no changes in electromyographic amplitude and mechanomyogrpahic amplitude.CONCLUSIONS:These findings suggested that these neuromuscular parameters did not track the fatigue-induced changes in MVIC torque after 5-min of recovery.

This study examined the electromyographic (EMG) responses from the vastus medialis (VM) for electrodes placed over and away from the innervation zone (IZ) during a maximal voluntary isometric contraction (MVIC) and sustained, submaximal isometric muscle action. A linear electrode array was placed on the VM to identify the IZ and muscle fiber pennation angle during an MVIC and sustained isometric muscle action at 50 % MVIC. EMG amplitude and frequency parameters were determined from 7 bipolar channels of the electrode array, including over the IZ, as well as 10 mm, 20 mm and 30 mm proximal and distal to the IZ. There were no differences between the channels for the patterns of responses for EMG amplitude or mean power frequency during the sustained, submaximal isometric muscle action; however, there were differences between channels during the MVIC. The results of the present study supported the need to standardize the placement of electrodes on the VM for the assessment of EMG amplitude and mean power frequency. Based on the current findings, it is recommended that electrode placements be distal to the IZ and aligned with the muscle fiber pennation angle during MVICs, as well as sustained, submaximal isometric muscle actions.

The purpose of this study was to investigate the effects of 4-weeks of high- versus low-load resistance training to failure on rate of torque development (RTD), electromechanical delay (EMD), and contractile twitch characteristics. Fifteen men (mean±SD; age=21.7±2.4 yrs) were randomly assigned to either a high- (80% 1RM; n=7) or low-load (30% 1RM; n=8) training group and completed elbow flexion resistance training to failure 3 times per week for 4 weeks. The participants were tested at baseline, 2-, and 4-weeks of training. Peak RTD (pRTDV) and RTD at 0-30 (RTD30V), 0-50 (RTD50V), 0-100 (RTD100V), and 0-200 (RTD200V) ms, integrated EMG amplitude (iEMG) at 0-30, 0-50, and 0-100 ms, and EMD were quantified during maximal voluntary isometric muscle actions. Peak twitch torque, peak RTD, time to peak twitch, 1/2 relaxation time and the peak relaxation rate were quantified during evoked twitches. Four weeks of high-load, but not low-load resistance training, increased RTD200V. There were also increases in iEMG during the first 30 ms of muscle activation for the high- and low-load groups, which may have indirectly indicated increases in early phase motor unit recruitment and/or firing frequency. There were no significant training-induced adaptations in EMD or contractile twitch properties.

13 subjects performed an incremental test to exhaustion, 4, 8-min submaximal rides, and a 1-h ride at the rating of perceived exertion (RPE) that corresponded to the physical working capacity at the OMNI threshold (PWC(OMNI)) to examine: 1) the oxygen consumption (V̇O2), heart rate (HR), minute ventilation (+V̇(E)), respiratory frequency (FR), and power output responses during 1-h work bouts at a constant RPE that corresponded to the PWC(OMNI); and 2) the ability of current models to explain the responses for physiological and perceptual parameters during the 1-h work bouts. The RPE that corresponded to the PWC(OMNI) represented a sustainable exercise intensity (56±5% (V̇O(2Peak)) within the moderate-intensity domain. The mean, normalized slope coefficients for the V̇O2, +V̇(E), and power output vs. time relationships during the 1-h rides were significantly less than zero. The mean, normalized slope coefficient for the FR vs. time relationship during the 1-h rides, however, was not significantly different from zero. Thus, RPE most clearly tracked FR responses during the 1-h rides. It was hypothesized that afferent feedback from respiratory muscles may have mediated the perception of effort during cycle ergometry at a constant RPE in the moderate-intensity domain.

This study examined the time courses of recovery for isometric peak torque and rate of torque development (RTD) after eccentric-induced muscle damage. 18 men completed 6 sets of 10 maximal eccentric isokinetic muscle actions at 30 degrees s(-1). Peak torque, peak RTD and RTD at 10 (RTD10), 50 (RTD50), 100 (RTD100) and 200ms (RTD200), serum creatine kinase and lactate dehydrogenase were measured before (PRE), immediately after (POST), 24, 48 and 72h after eccentric exercise. Creatine kinase and lactate dehydrogenase increased from 139 to 6457 and from 116 to 199IUL(-1) from PRE to 72h, respectively. Peak torque and all RTDs decreased at POST. Peak torque and RTD200 remained lower than PRE through 72h. Peak RTD remained lower than PRE through 48h, but was not different from PRE at 72h. RTD10 and RTD100 were lower than PRE through 24h, but were not different from PRE at 48 and 72h. RTD50 decreased at POST, but was not different from PRE at 24h. Early phase RTDs recovered more quickly than PT and RTD200. Early phase RTDs may reflect neural mechanisms underlying eccentric-induced force decrements, while late RTDs may describe the same physiological mechanisms as PT.

Previous studies have indicated that skinfold thickness (SKF) acts as a low-pass filter to the mechanomyographic (MMG) signal. PURPOSE: The purpose of this study was to examine the effects of SKF at four different locations on the vastus lateralis (VL) muscle on MMG amplitude and mean power frequency (MPF) responses during incremental cycle ergometry. METHODS: Twenty adults (age ± SD = 23.8 ± 3.0 years) volunteered to participate in the investigation. An orientation session was performed to determine the location of the innervation zone (IZ) for the VL using a linear electrode array. The MMG signals from the VL muscle were detected during an incremental cycle ergometry test using four accelerometers placed on the right VL proximal (Prox1), over (Over IZ), and distal (Dist IZ) to the IZ. A fourth accelerometer was placed at the site recommended by the SENIAM Project (Prox2) for the placement of EMG electrodes. Prior to the test, three SKF were taken at each accelerometer placement site. The mean of the three SKF at each site were used for the analysis. The subjects were divided (at the median SKF value) into two groups of smaller (n = 10) and larger (n = 10) SKF values. Simple linear regression analyses were performed for SKF vs. MMG amplitude and MPF at each location for power outputs of 50, 75, 100, 125, 150, and 175W. Independent t-tests were also performed between the smaller and larger SKF groups for SKF measurements, MMG amplitude, and MMG MPF values at each accelerometer placement site. An alpha of p ≤ 0.05 was considered statistically significant for all analyses. RESULTS: For the 48 regression analyses, there were only 2 significant relationships (r = −0.461 and −0.519) between the SKF values and MMG MPF and 3 significant relationships between the SKF values and MMG amplitude (r = −0.535, −0.456, and −0.443). The independent t-tests showed that there were significant mean differences between the smaller and larger SKF groups for SKF measurements for all accelerometer placements sites. Of the 48 mean comparisons, only 1 was significantly different between the smaller and larger SKF groups for MMG MPF and 4 for MMG amplitude. CONCLUSIONS: The present study showed that, in general, SKF values were not correlated with the MMG signal. Only 10% of the regression analyses for SKF versus MMG MPF and MMG amplitude were statistically significant. In addition, only 10% of the mean comparisons between smaller and larger SKF groups for MMG MPF and MMG amplitude were significantly different. Thus, the results of the present study indicated that the larger SKF values did not attenuated the MMG signal. Other factors, including changes in force production and muscle length, as well as factors related to the accelerometer location, such as amount of muscle mass, muscle architecture, and/or motor unit territorial distribution may have had a greater effect on the MMG signal than SKF. PRACTICAL APPLICATIONS: These findings indicated that, in generall, smaller and larger SKF values did not correlate with the amplitude and frequency parameters of the MMG signal. Thus, there may be other anatomical, physiological, or methodological factors that have a greater effect on the MMG signal. These findings provide information about a methodological consideration necessary for the interpretation of the MMG signal.

PURPOSE: To examine the influence of electrode placement on the physical working capacity at the fatigue threshold (PWCFT). The PWCFT test estimates the highest power output that can be maintained without neuromuscular evidence of fatigue and is determined from the rate of increase in the amplitude of the electromyographic (EMG) signal. METHODS: Fifteen college-aged males and females (mean age ± SD = 22.6 ± 3.4 yr; BW = 74.3 ± 11.2 kg; HT = 176.1 ± 9.0 cm) performed an incremental test to exhaustion on a cycle ergometer. A linear electrode array was utilized to determine the location of the innervation zone (IZ) and muscle fiber pennation angle (MFPA) of the vastus lateralis (VL). For determination of the PWCFT values, surface EMG signals were recorded from 3 bipolar electrode arrangements at different locations over the VL during the incremental tests. The first electrode arrangement was placed on the VL at one-third of the distance between the lateral border of the patella and the anterior superior iliac spine, and oriented parallel to the MFPA. The second electrode arrangement contained the same center point as the first electrode arrangement, but was oriented parallel to the long axis of the femur. A third electrode arrangement was placed over the IZ and oriented parallel to the MFPA. RESULTS: The results of a one-way ANOVA indicated there were no significant (p < 0.05) mean differences in PWCFT values among the 3 electrode placements (parallel to the MFPA = 181 ± 40 W; parallel to the long axis of the femur = 185 ± 44 W; and over the IZ = 189 ± 54 W). In addition, there were significant correlations in PWCFT values for the electrode placement parallel to the MPFA vs. parallel to the long axis of the femur (r = 0.94) and over the IZ (r = 0.88), as well as for the electrode placement parallel to the long axis of the femur vs. over the IZ (r = 0.81). CONCLUSIONS: These findings indicated that the PWCFT test is not influenced by the placement of a bipolar electrode arrangement in relation to the MFPA or over the IZ. Practical Applications: The results of the current study suggested that the onset of neuromuscular fatigue (PWCFT) can be estimated without identification of the MFPA or IZ.

It has been suggested that the thickness of the subcutaneous tissue layer affects time and frequency domain parameters of the surface electromyography (EMG) signal. PURPOSE: The purpose of the present study was to examine the effects of skinfold thickness on the amplitude and mean power frequency (MPF) of the EMG signal from the vastus lateralis (VL) muscle during cycle ergometry. METHODS: Twenty adults (13 men and 7 women; mean age ± SD = 23.8 ± 3.0 yr) volunteered for this study. A bipolar surface EMG electrode configuration (30 mm center-to-center distance) was placed over the vastus lateralis (VL) muscle at one-third of the distance from the lateral border of the patella to the anterior superior iliac spine. EMG amplitude and MPF values were measured during incremental cycle ergometry at 50, 75, 100, 125, and 175 W. The incremental cycle ergometry test began at 50 W and increased by 25 W every 2 min. In addition, three skinfold measurements (mm) were taken from the VL at the site of the EMG electrode placement with the average value used in subsequent analyses. Simple linear regression was used to determine the relationships for EMG amplitude and MPF versus skinfold thickness at each power output. In addition, independent t-tests were used to compare the mean values for EMG amplitude and MPF between the 10 subjects with the largest skinfold values (mean ± SD = 16.7 ± 5.2 mm) and those (n = 10) with the smallest skinfold values (mean ± SD = 6.6 ± 1.2 mm). RESULTS: The simple linear regression analyses revealed no significant (p > 0.05) correlations between skinfold thickness and EMG amplitude (r = 0. 18 – 0.40) or MPF (r = 0. 17 – 0.41) at any of the power outputs. Furthermore, there were no significant mean differences (p > 0.05) in EMG amplitude or MPF between the subjects with the largest skinfold values and those with the smallest skinfold values. CONCLUSIONS: The results of the present study indicated that skinfold thickness did not affect absolute values for EMG amplitude or MPF from the VL muscle during cycle ergometry at five power outputs. These findings suggest that there maybe differences between the results of simulation studies and measured findings from surface EMG studies. PRACTICAL APPLICATIONS: Subcutaneous tissue thickness is just one of many possible factors that can affect the amplitude and frequency domains of the EMG signal. Other factors include the conductivities of the tissue, interelectrode distance, and the number of recruited motor units. The current findings provide information regarding a methodological consideration associated with the application of surface EMG measurements.

The purposes of this study were twofold: 1) to derive the mechanomyographic mean power frequency fatigue threshold (MMG MPFFT) for submaximal cycle ergometry; and 2) to compare the power outputs associated to the MMG MPFFT to other neuromuscular and gas exchange fatigue thresholds. 9 adults (5 men and 4 women; mean+/-SD age=23.7+/-3.7 years; body weight=66.3+/-8.2 kg) performed an incremental cycle ergometry test to exhaustion while expired gas samples, electromyographic (EMG), and MMG signals were measured from the vastus lateralis muscle. The non-significant correlations (r=0.17 to 0.66; p>0.05) among the physical working capacity at the fatigue threshold (PWCFT), MMG MPFFT, and gas exchange threshold (GET) suggested that different physiological mechanisms may underlie these 3 fatigue thresholds. A significant correlation (r=0.83) for the MPFFT vs. respiratory compensation point (RCP) suggested that these fatigue thresholds may be mediated by a common physiological mechanism. In addition, the significantly lower mean values found for the PWCFT (mean+/-SD=163+/-43 W), MMG MPFFT (132+/-33 W), and GET (144+/-28 W) than MPFFT (196+/-53 W) and RCP (202+/-41 W) suggested that these gas exchange and neuromuscular fatigue thresholds may demarcate different exercise intensity domains.

UNLABELLED:The electromyographic (EMG) mean power frequency (MPF) and amplitude versus time relationships are commonly used to characterize localized muscle fatigue.PURPOSE:The purpose of this study was to compare the effect of epoch length on the individual and mean slope coefficients and y-intercepts resulting from the EMG MPF and amplitude versus time relationships of the vastus medialis (VM) muscle during fatiguing isometric muscle actions at 30 and 75% of maximum voluntary isometric contraction (MVC).METHODS:Eight adults performed two continuous, isometric muscle actions of the leg extensors at 30 and 75% MVC to exhaustion. Six, 5.0 s epochs of the surface EMG signals were recorded from the VM during each minute. Epoch lengths of 0.5, 1.0, and 2.0 s were selected from the middle of each 5.0 s epoch. Linear regression was used to estimate the slope coefficient and y-intercept values for the EMG MPF and amplitude versus time relationships for each epoch length (0.5, 1.0, 2.0, and 5.0 s) and subject.RESULTS:There were no significant differences between epoch lengths for the individual or mean slope coefficients or y-intercepts (EMG MPF and amplitude versus time relationships).CONCLUSION:This study indicated that epochs of 0.5 - 5.0 s resulted in the same characterization of EMG (MPF and amplitude) versus time relationships during isometric muscle actions.

The purposes of this study were threefold: (1) to compare the isometric torque-related patterns of absolute and normalized electromyographic (EMG) amplitude and mean power frequency (MPF) responses for electrode orientations that were parallel and perpendicular to the muscle fibers; (2) to examine the influence of electrode orientation on mean absolute EMG amplitude and MPF values; and (3) to determine the effects of normalization on mean EMG amplitude and MPF values from parallel and perpendicular electrode orientations. Ten adults (5 men and 5 women mean +/- SD age = 23.8 +/- 2.3 years) volunteered to participate in the investigation. Two sets of bipolar surface EMG electrodes (20 mm center to center) were placed parallel and perpendicular to the muscle fibers over the biceps brachii. The subjects performed a maximal voluntary isometric contraction (MVIC) test followed by randomly ordered submaximal muscle actions in 10% increments from 10 to 90% MVIC. Paired t-tests indicated that absolute EMG amplitude values for the parallel electrode orientation were greater (p < 0.05) than those for the perpendicular orientation at all isometric torque levels except 10% MVIC For normalized EMG amplitude values, however, there were no significant mean differences between electrode orientations. There were also no differences between electrode orientations for absolute or normalized EMG MPF values. In 30% of the cases, different torque-related patterns of responses were observed between the parallel and perpendicular electrode orientations for the absolute and normalized EMG amplitude and MPF values. Therefore, the results of the present study support the need for standardizing electrode orientation to compare the pattern of responses for EMG amplitude and MPF values and normalizing EMG amplitude data to compare the mean values.

The purposes of this study were to (a) determine if the mathematical model used to estimate the physical working capacity at the oxygen consumption threshold (PWC(VO(2))) and physical working capacity at the heart rate threshold (PWC(HRT)) for cycle ergometry could be applied to treadmill running; (b) propose new fatigue thresholds called the running velocity at the oxygen uptake threshold (RV(VO(2))) and running velocity at the heart rate threshold (RV(HRT)) for treadmill exercise; and (c) statistically compare the velocities at the RV(VO(2)), RV(HRT), and ventilatory threshold (VT). Seven aerobically trained adult volunteers (mean +/- SD: age 24.0 +/- 3.9 years, Vo(2) max 56.7 +/- 7.1 ml.kg(-1).min(-1)) performed a maximal treadmill test to determine Vo(2) peak and VT as well as four 8-minute submaximal workbouts for the determination of RV(VO(2)) and RV(HRT). One-way repeated-measures analysis of variance indicated that there were no significant (p > 0.05) mean differences among the running velocities for the RV(VO(2)), RV(HRT), and VT. The results of this study indicated that the mathematical model used to estimate PWC(VO(2)) and PWC(HRT) for cycle ergometry could be applied to treadmill running. Furthermore, the RV(VO(2)) and RV(HRT) test may provide submaximal techniques for estimating the VT.

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.

PURPOSE The purpose of this study was to compare the relative efficiency of two predictive models of a law enforcement officer physical agility criterion task test. METHOD Data were gathered on 121 male law enforcement officer recruits (mean±SD age = 26.9±5.1 yrs) at the Nebraska Law Enforcement Training Center who participated in mandatory fitness training (1h•d−1, 3 d•wk−1) as part of a 12-week basic law enforcement training program. Multiple regression analyses were conducted to examine the research hypothesis that 1.5 mile run times (CRF), percent body fat (PERFAT), leg press/body weight ratio (LEGRATIO), bench press/body weight ratio (BENCHRATIO), and abdominal muscular endurance (SITUPS) combine to produce a sufficient predictive model on a criterion task test model of law enforcement officer physical agility (LEOPAT), and that upper body 1-RM strength (BENCHPRESS), lower body 1-RM strength (LEGPRESS), sit-reach flexibility (FLEX), and lean body mass (LBM) would not further improve the predictive utility of the model. RESULTS The model including the five variables accounts for a significant proportion of variance (R 2 = .389, F(2,120)=14.649, p = .0001), which is consistent with the hypothesis. When BENCHPRESS, LEGPRESS, FLEX, and LBM were added to the equation, the variance accounted for increased to R 2 = .403 (F(2,120) = 10.461 p = .0001) which was not significantly more than the variance accounted for by the smaller model (F-change(1,114) = 1.205, p = .275). Consistent with the hypothesis, none of the additional four predictors contributed to this larger model. CONCLUSION Together these results provide support for the hypothesis that the 5-variable model used to predict performance on the LEOPAT was more efficient than the 9-variable model. Inclusion of SITUPS, PERFAT, FLEX, and LBM do not increase the predictive utility of the model further.

The purpose of this study was to compare changes in selected physical performance and fitness variables in male law enforcement officer (LEO) recruits between instructor-led (IL) and voluntary (VOL) physical fitness programs. Subjects participated in either a mandatory physical conditioning program (IL, n = 121, age ± SD = 27 ± 5 yrs) three times per week or a voluntary physical conditioning program (VOL, n = 81, age = 28 ± 7 yrs) during 12 weeks of basic LEO recruit training. Pre-training (PRE) and post-training (POST) measures were recorded for the following variables: 1.5 mile run time (1.5); sit-reach test (SR); absolute 1 RM leg press strength (LPA); absolute 1 RM bench press strength (BPA); 1 RM leg press/body weight ratio (LPR); 1 RM bench press/body weight ratio (BPR); sit-ups (SU); total body weight (BW); and the Law Enforcement Officer Physical Agility Test (LEOPAT). Separate two-way, mixed factorial ANOVAs (group × time) revealed a significant interaction (p < 0.05) for 1.5, but no interactions for SR, LPA, LPR, BPA, BPR, SU, BW, or LEOPAT. Paired-data t-tests indicated significant (p < 0.05) improvements from PRE to POST for all variables except BW. Independent samples t-tests indicated significant (p < 0.05) differences between the VOL and IL groups for 1.5 and the marginal means (collapsed across PRE and POST) for LPR, SU, and LEOPAT. There were, however, no significant differences (p > 0.05) between the VOL and IL groups for the marginal means for SR, LP, BP, BPR, and BW. These results indicated that the IL, group had significantly better scores for the 1.5, LPR, SU, and LEOPAT at both PRE and POST, however, improvements across time for the SR, LP, BP, BPR and BW were independent of individual group effects (VOL or IL). These data have implications regarding program design and effectiveness for improving physical fitness variables that directly impact short-term and long-term law enforcement officer readiness and survival.Table