Patellofemoral pain and the mechanomyographic responses of the vastus lateralis and vastus medialis muscles.

The purpose of this investigation was to examine the influence of patellofemoral pain (PFP) on the amplitude of the mechanomyographic (MMG) and electromyographic (EMG) signals from the vastus lateralis and vastus medialis muscles of the quadriceps femoris. Nine females reporting current signs and symptoms of PFP and 8 healthy females service as the control (CTL) group volunteered to participate in this study. Participants completed maximal and submaximal (25, 50, 75% MVC) isometric muscle actions of the quadriceps femoris at a leg flexion angle of 45 degrees below the horizontal plane of the lever arm. The involved limb for the PFP group and the dominant limb for the CTL group were selected for testing and all submaximal force levels were randomized. There was no (p > 0.05) group difference in EMG amplitude response for any muscle at any % MVC level. For the MMG amplitude, however, there was a main effect (p < 0.05) for group where the control group demonstrated greater MMG amplitude for each muscle. These findings suggest that the presence of PFP influenced mechanical aspect of muscle function as measured by MMG, but not the electrical properties (EMG). MMG may provide unique insight into the intrinsic effects on muscle function due to PFP.

Cross-correlation analyses of mechanomyographic signals from the superficial quadriceps femoris muscles during concentric and eccentric isokinetic muscle actions.

The purpose of this investigation was to examine the cross-correlation coefficients of mechanomyographic (MMG) signals recorded from the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles during maximal, concentric and eccentric isokinetic muscle actions. Eleven females (mean +/- SD age = 21 +/- 1 yr) performed such muscle actions of the leg extensors at 60 degrees.s-1 on a Cybex 6000 dynamometer. MMG signals were sampled simultaneously from the VL, RF, and VM at 1000 Hz by piezoelectric crystal contact sensors. Peak composite cross-correlation coefficients (rxy) and common variances (rxy2) were determined for each between-muscle comparison (VL vs. RF, VL vs. VM, and RF vs. VM). The results indicated peak cross-correlation coefficients ranging from rxy = 0.38 to 0.52, while common variances (rxy2) between signals ranged from 14% to 27% across all time lags (tau = -50...). In conjunction with other studies, these results suggested that despite the potential for some cross-talk, MMG measurements can be used to examine differences between the patterns of MMG amplitude and frequency responses of the superficial quadriceps femoris muscles.

The effect of concentric isokinetic strength training of the quadriceps femoris on electromyography and muscle strength in the trained and untrained limb.

The purpose of the present investigation was to examine the effects of unilateral concentric isokinetic leg extension training on peak torque (PT) and electromyographic (EMG) responses in the trained and untrained limbs. Twenty adult men were randomly assigned to a training (TRN, n = 11) or control (CTL, n = 9) group. The TRN group performed 6 sets of 10 leg extensions 3 days per week for 12 weeks at a velocity of 90 degrees.s(-1). All subjects were tested every 4 weeks for PT and EMG responses of both legs at a velocity of 90 degrees.s(-1). The 3-way mixed factorial analysis of variance (ANOVA) indicated a significant (p < 0.05) increase in PT over the 12 weeks in both the trained and untrained limb for the TRN group but no significant change in PT in either limb for the CTL group. The results of the 3-way ANOVA for the EMG data indicated no significant change in EMG amplitude in the trained or untrained limb for the TRN or CTL group. The increase in PT in the absence of a change in EMG may result from hypertrophic factors and/or changes in the other muscles or muscle groups involved in leg extension.

Heart rate and ratings of perceived exertion at the physical working capacity at the heart rate threshold.

The purpose of this investigation was to examine the heart rate (HR) responses and ratings of perceived exertion (RPE) during continuous work bouts at 80, 100, and 120% of the physical working capacity at the heart rate threshold (PWCHRT). Ten men (mean age +/- SD = 23.3 +/- 2.9 years) performed a maximal cycle ergometer test and four, 8-minute submaximal work bouts for the determination of PWCHRT. Each subject then performed 3 continuous 1-hour work bouts at 80, 100, and 120% of the power output corresponding to PWCHRT. The results of the 1-hour work bouts showed that slope coefficients for the mean HR vs. time relationships for all 3 power outputs were significantly (p < 0.05) greater than zero and 0.1 bpm x min(-1). In addition, the slope coefficients for mean RPE vs. time relationships for all 3 power outputs were significantly (p < 0.05) greater than zero. The mean slope coefficients for the HR and RPE vs. time relationships indicated that the PWCHRT test overestimated the maximal power output associated with steady-state HR and RPE responses. The mean HR slope coefficient suggested, however, that the PWCHRT could be maintained for over 4 hours.

Mean power frequency and amplitude of the mechanomyographic and electromyographic signals during incremental cycle ergometry.

The purpose of this investigation was to determine the relationships for mechanomyographic (MMG) amplitude, MMG mean power frequency (MPF), electromyographic (EMG) amplitude, and EMG MPF versus power output during incremental cycle ergometry. Seventeen adults volunteered to perform an incremental test to exhaustion on a cycle ergometer. The test began at 50 W and the power output was increased by 30 W every 2 min until the subject could no longer maintain 70 rev min(-1). The MMG and EMG signals were recorded simultaneously from the vastus lateralis during the final 10 s of each power output and analyzed. MMG amplitude, MMG MPF, EMG amplitude, EMG MPF, and power output were normalized as a percentage of the maximal value from the cycle ergometer test. Polynomial regression analyses indicated that MMG amplitude increased (P<0.05) linearly across power output, but there was no change (P>0.05) in MMG MPF. EMG amplitude and MPF were fit best (P<0.05) with quadratic models. These results demonstrated dissociations among the time and frequency domains of MMG and EMG signals, which may provide information about motor control strategies during incremental cycle ergometry. The patterns for amplitude and frequency of the MMG signal may be useful for examining the relationship between motor-unit recruitment and firing rate during dynamic tasks.

Mechanomyography, electromyography, heart rate, and ratings of perceived exertion during incremental cycle ergometry.

BACKGROUND: The purpose of this investigation was to examine the relationships of mchanomyography (MMG), electromyography (EMG), heart rate (HR), and ratings of perceived exertion (RPE) versus power output during incremental cycle ergometry. METHODS: Nine adult males [mean (+/-SD) age 23 (+/-3) years] volunteered to perform an incremental test to exhaustion on a cycle ergometer. The MMG, EMG, HR, and RPE values were recorded at the end of each power output. RESULTS: The normalized (expressed as a percentage of maximal values) relationships for MMG, HR, and RPE versus power output were linear, while the EMG versus power output relationship was quadratic. Furthermore, there were no significant (p > 0.10) differences between slope coefficients for the relationships among MMG, HR, and RPE versus power output. CONCLUSIONS: The results of this investigation indicated that there were close associations among the mechanical (MMG), cardiac (HR), and perception of effort (RPE) aspects of cycle ergometry. In addition, there was a dissociation between the linear MMG pattern and quadratic EMG pattern with increasing power outputs.

Mechanomyographic responses to continuous, constant power output cycle ergometry.

PURPOSE: The purpose of the present investigation was to examine the mechanomyographic (MMG) and electromyographic (EMG) responses to continuous, constant power output cycle ergometer workbouts. METHODS: Eight adult male volunteers (mean age +/- SD = 22 +/- 2 yrs) performed three continuous, one-hour workbouts at 28, 35, and 42% of peak power (Ppeak). RESULTS: The slope coefficients for the mean normalized MMG amplitude versus time relationships were significantly (p < 0.05) less than zero, while the slope coefficients for the mean normalized EMG amplitude versus time relationships were significantly (p < 0.05) greater than zero. CONCLUSION: The results indicated dissociation between the patterns of the mechanical (MMG) and electrical (EMG) activity of the vastus lateralis during continuous cycle ergometry at low power outputs. The increases in EMG amplitude were likely due to the recruitment of additional motor units. The decreases in MMG amplitude across time may have been due to the phenomenon known as "muscular wisdom" and/or decreases in muscular compliance.

Mechanomyographic amplitude and mean power output during maximal, concentric, isokinetic muscle actions.

The purpose of this study was to determine the velocity-related patterns for mechanomyographic (MMG) amplitude, electromyographic (EMG) amplitude, mean power output (MP), and peak torque (PT) of the superficial muscles of the quadriceps femoris (vastus lateralis [VL], rectus femoris [RF], and vastus medialis [VM]) during maximal, concentric, isokinetic leg extensions. Twelve adult women (mean +/- SD: 22 +/- 3 years of age) performed such leg extensions at velocities of 60 degrees, 120 degrees, 180 degrees, 240 degrees, and 300 degrees /s on a Cybex 6000 dynamometer. PT decreased (P < 0.05) across velocity to 240 degrees /s. MP and MMG amplitude for each muscle (VL, RF, and VM) increased (P < 0.05) with velocity to 240 degrees /s and then plateaued. EMG amplitude increased (P < 0.05) to 240°/s for the VL, remained unchanged across velocity (P > 0.05) for the RF, and increased (P < 0.05) to 300 degrees /s for the VM. The results indicated close similarities between the velocity-related patterns for MMG amplitude and MP, but dissociations among EMG amplitude, MMG amplitude, and PT. These findings support the recent hypothesis that MMG amplitude is more closely related to MP than PT during maximal, concentric, isokinetic muscle actions and, therefore, may be useful for monitoring training-induced changes in muscle power.

The effect of leg extension training on the mean power frequency of the mechanomyographic signal.

The purpose of the present investigation was to examine the effect of concentric isokinetic leg extension training on the mean power frequency (MPF) of the mechanomyographic (MMG) signal. Twenty-one men were assigned into a training (TRN; n = 12) or control (CTL; n = 9) group. The TRN group performed six sets of leg extensions 3 days per week for 12 weeks at a velocity of 90 degrees /s. All subjects were tested every 4 weeks for peak torque (PT), while MMG was recorded from the vastus lateralis. PT increased, but there was no significant (P > 0.05) change in the MMG MPF over the 12-week training period. These results indicate that MMG MPF, measured from the vastus lateralis, was not sensitive to training-induced increases in leg-extension strength, possibly due to competing influences of hypertrophy on the MMG signal and/or training-induced adaptations in muscles other than the vastus lateralis.

The effects of leg angular velocity on mean power frequency and amplitude of the mechanomyographic signal.

The purpose of the present investigation was to examine the effects of leg angular velocity on the mean power frequency (MPF) and amplitude of the mechanomyographic (MMG) signal during maximal concentric (CON) isokinetic muscle actions. Sixteen adult subjects performed maximal CON leg extensions on a calibrated Cybex 6000 dynamometer at leg angular velocities of 60 and 300 degrees.s-1. MMG was detected by a piezoelectric crystal contact sensor placed over the mid-portion of the vastus lateralis muscle. The results indicated a significant (p < 0.05) velocity-related decrease in peak torque (PT) and increase in MMG amplitude from 60 to 300 degrees.s-1. There was, however, no velocity-related change (p > 0.05) in MMG MPF. These findings did not support our hypothesis that increases across velocity in MMG amplitude were due to decreases in muscle stiffness as a result of a shift in the contribution of slow and fast-twitch muscle fibers to PT production. Future research should examine the potential influence of actin-myosin cycling rate as well as limb movement on the MPF and amplitude of the MMG signal.

Mechanomyographic and electromyographic responses during submaximal cycle ergometry.

The purpose of this study was to examine the mechanomyographic (MMG) and electromyographic (EMG) responses during continuous, cycle ergometer workbouts performed at constant power outputs. Eight adults [mean (SD) age, 21.5 (1.6) years] volunteered to perform an incremental test to exhaustion for the determination of peak power (Wpeak) and four, 15-min (or to exhaustion) rides at constant power outputs of 50%, 65%, 80%, and 95% Wpeak. Piezoelectric crystal contact sensors were placed on the vastus lateralis (VL) and vastus medialis (VM) muscles to record the MMG signals. Bipolar surface electrode arrangements were placed on the VL and VM to record the EMG signals. Five-second samples of the MMG and EMG signals were recorded every 30 s at power outputs of 50%, 65%, and 80% Wpeak, and every 15 s at 95% Wpeak. The amplitudes of the selected portions of the signals were normalized to the first values recorded during the continuous rides, and regression analyses were used to determine whether the slope coefficients for the MMG and EMG versus time relationships were significantly (P < 0.05) different from zero. The results indicate that EMG amplitude increased (range of slope coefficients: 0.03-0.56) during the continuous rides for both muscles at all four power outputs (except the VM at 50% Wpeak), while MMG amplitude increased (slope coefficient at 95% Wpeak for VM = 0.19), decreased (range of slope coefficients for VL and VM at 50% and 65% Wpeak = -0.14 to -0.24), or remained unchanged (range of slope coefficients for VL and VM at 80% Wpeak and VL at 95% peak = -0.06 to 0.12) depending on the power output. The patterns of the MMG responses, however, were similar for the VL and VM muscles, except at 95% Wpeak. Fatigue-induced changes in motor-unit recruitment and discharge rates, or muscular compliance may explain the differences between power outputs in the patterns of the MMG amplitude responses.

Allometric scaling of isokinetic peak torque: the Nebraska Wrestling Study.

Allometric scaling has been used increasingly in the exercise sciences to control statistically for body size differences in physical performance variables. The purpose of this study was to use multivariate allometric scaling to examine the influence of fat-free mass (FFM) on age-related differences in strength in young club (8-13 years) and high-school (14-18 years) wrestlers. The dependent variables were log-transformed values of isokinetic peak torque for leg extension and flexion at 0.52, 3.14, and 5.24 rad x s(-1)(30, 180, and 300 x s(-1)). The independent variables used in the multiple regression analyses were log-transformed values for FFM, age, and the FFM versus age interaction. The resulting regression equations were of the form: log Y = log a + b1 log X1 + b2 log X2 + bn log Xn. The initial multiple regression analyses showed significant interaction effects (P < 0.05) for all dependent variables, therefore separate regression analyses were performed for the younger and older groups of wrestlers. The results indicate that for the younger wrestlers there were increases in isokinetic peak torque at all velocities across age after controlling for FFM. The FFM scaling exponents ranged from 0.94 to 1.31. All exponents included 1.0 in the 95% confidence interval, except for extension at 3.14 rad x s(-1). For the high-school wrestlers, both FFM and age were significant for the extension data, but only FFM was significant for the flexion data. All FFM exponents included 1.0 in the 95% confidence interval. These results indicate that the relationship between FFM and peak torque differed across age. In addition, with the exception of the flexion data for the high-school wrestlers, within each group increases in isokinetic peak torque occurred across age, independent of increases in FFM. The causes of the age effect for strength are speculative, but it may be due to developmental changes in neuromuscular function, alterations in the distribution of muscle mass as a percentage of FFM and/or the distribution of FFM across body segments.

MMG and EMG responses of the superficial quadriceps femoris muscles.

Eighteen adults performed isometric muscle actions of the leg extensors at 25, 50, 75, and 100% maximal voluntary contraction (%MVC) at leg flexion angles of 25, 50, and 75 degrees. The results indicated that isometric torque production increased as leg flexion angle increased (75 degrees > 50 degrees > 25 degrees). For each muscle tested (rectus femoris, vastus lateralis, and vastus medialis), the EMG amplitude increased up to 100%MVC at each leg flexion angle (25, 50, and 75 degrees). The MMG amplitude for each muscle, however, increased up to 100%MVC at 25 and 50 degrees of leg flexion, but plateaued from 75 to 100%MVC at 75 degrees of leg flexion. We hypothesize that the varied patterns for the MMG amplitude-isometric torque relationships were due to leg flexion angle differences in: (1) muscle stiffness, (2) intramuscular fluid pressure, or (3) motor unit firing frequency.

Mean power frequency and amplitude of the mechanomyographic signal during maximal eccentric isokinetic muscle actions.

The purpose of the present investigation was to examine the effects of knee angular velocity on the mean power frequency (MPF) and amplitude of the mechanomyographic (MMG) signal during maximal eccentric (ECC) isokinetic muscle actions. Eleven adult subjects performed maximal ECC muscle actions of the leg extensors on a calibrated Cybex 6000 dynamometer at knee angular velocities of 60, 120, and 180 degrees.s-1. MMG was detected by a piezoelectric crystal contact sensor placed over the vastus lateralis muscle. There were no significant (p > 0.05) velocity-related changes in ECC peak torque (PT) or MMG MPF, however, the mean MMG amplitude value at 60 degrees.s-1 was significantly less (p < 0.05) than that at 180 degrees.s-1. These results did not support our previous hypothesis that the velocity-related increase in MMG amplitude for maximal ECC isokinetic muscle actions was due to selective recruitment of fast twitch fibers and derecruitment of slow twitch fibers with increasing velocity.

Gender comparisons of the mechanomyographic responses to maximal concentric and eccentric isokinetic muscle actions.

PURPOSE: The purpose of this study was to determine whether there is a gender difference in the velocity-related patterns of mechanomyographic (MMG) responses to maximal isokinetic concentric (CON) and eccentric (ECC) muscle actions. METHODS: Adult males (N = 15) and females (N = 16) performed maximal CON and ECC muscle actions of the leg extensors on a calibrated Cybex 6000 dynamometer at velocities of 30, 90, and 150 degrees.s-1. MMG was detected by a piezoelectric crystal contact sensor placed over the vastus lateralis muscle. RESULTS: The results indicated that there were decreases in CON peak torque (PT) across velocities, while ECC PT remained constant with increasing velocity for both genders. MMG amplitude increased significantly (P < 0.05) with velocity in both the males and females for CON and ECC muscle actions. There was a gender difference in the velocity-related patterns of MMG responses to maximal isokinetic CON muscle actions; however, there was no gender difference in the pattern of ECC MMG responses. CONCLUSIONS: The gender difference in CON MMG responses may be attributed to the greater percent decline in CON PT across velocity for the females than the males. In addition, the males displayed greater CON and ECC MMG amplitudes at all muscle action velocities than the females, possibly because of gender differences in muscle mass and/or thickness of the adipose tissue layer.

Mechanomyographic and electromyographic responses to eccentric and concentric isokinetic muscle actions of the biceps brachii.

The purpose of the present investigation was to examine the effects of forearm angular velocity on the mechanomyographic (MMG) and electromyographic (EMG) responses to eccentric and concentric isokinetic muscle actions. Ten adult male volunteers (mean+/-SD age=23+/-2 years) performed maximal eccentric and concentric muscle actions of the forearm flexors at 30 degrees, 90 degrees, and 150 degrees s(-1). There was no significant (P> 0.05) velocity-related change in peak torque (PT) for the eccentric muscle actions, but there was a significant (P < 0.05) decrease in PT for the concentric muscle actions. For the eccentric and concentric muscle actions, there was a significant (P< 0.05) velocity-related increase in MMG amplitude. There was no significant (P < 0.05) change in EMG amplitude across velocity for the eccentric or concentric muscle actions. The results indicated velocity-related dissociations among the PT, MMG, and EMG responses to maximal eccentric and concentric isokinetic muscle actions.

The effect of leg flexion angle on the mechanomyographic responses to isometric muscle actions.

The purpose of this investigation was to examine the effect of leg flexion angle on the relationship between mechanomyographic (MMG) amplitude and isometric torque production. Adult males (n = 9) performed isometric muscle actions of the leg extensors at 25, 50, 75, and 100 percent maximal voluntary contraction (%MVC) on a calibrated CYBEX 6000 dynamometer at 25, 50, and 75 degrees below full extension. A piezoelectric MMG recording device was placed over the mid-portion of the rectus femoris. At 25 degrees of leg flexion, the MMG amplitude increased to 100%MVC. At 50 and 75 degrees of leg flexion, however, MMG amplitude increased to 75%MVC, and then did not change significantly (P > 0.05) between 75 and 100%MVC. These findings indicate that the MMG amplitude-isometric torque relationship is joint angle specific and may be the result of leg flexion angle differences in: (1) muscle stiffness, or (2) motor unit activation strategies.

Validity of bioelectrical impedence equations for estimating fat-free weight in high school female gymnasts.

The present study examined the validity of bioelectrical impedence (BIA) equations for estimating fat-free weight (FFW) in female gymnasts by comparing the values to those obtained from underwater weighing (UWW). Ninety-seven female Caucasian high school gymnasts (mean age +/- SD = 15.7 +/- 1.1 yr) participated in the study. FFW from UWW was calculated from percent fat using the revised formula of Brozek et al. (mean FFW +/- SD = 43.8 +/- 4.5 kg) and the age-specific constants of Lohman (mean FFW +/- SD = 44.8 +/- 4.6 kg). Cross-validation analyses included examination of the constant error (CE), SEE, r, and total error (TE). The results indicated similar trends between equations when based on either the Brozek or Lohman conversions; however, the CE, SEE, and TE values were consistently lower for the majority of the equations using the revised formula of Brozek et al. Based upon the results of the cross-validation analyses, the equation of Houtkooper et al. and the interlaboratory equations of Van Loan et al. and Lohman, which resulted in identical TE values of 2.4 kg are recommended for use with young high school gymnasts.

Mechanomyographic responses to maximal eccentric isokinetic muscle actions.

The purpose of the present investigation was to examine the mechanomyographic (MMG) responses to maximal eccentric isokinetic muscle actions. Eight adult male volunteers [age 22 +/- 2 (SD) yr] performed maximal eccentric muscle actions of the leg extensors at 60, 90, 120, and 180 degrees /s on a Cybex 6000 isokinetic dynamometer. MMG was detected by a piezoelectric crystal contact sensor placed over the vastus lateralis muscle. Test-retest intraclass correlations ranged from R = 0.88 to 0.97 for peak torque and from R = 0.97 to 0.98 for root mean square MMG amplitude values. There was no significant (P > 0.05) velocity-related change in eccentric peak torque; however, there was a significant (P < 0.05) increase in MMG between 60 [119 +/- 44 (SE) mV] and 180 degrees/s (302 +/- 128 mV). These findings indicated a velocity-related dissociation between MMG and peak torque for maximal eccentric isokinetic muscle actions.

Mechanomyographic responses to concentric isokinetic muscle contractions.

The purpose of this investigation was to examine the effects of velocity of contraction on the mechanomyographic (MMG) responses to maximal concentric isokinetic leg extension movements. Eight adult males [mean (SD) age, 22.3 (1.3) years] performed maximal leg extensions on a calibrated Cybex 6000 dynamometer at velocities of 60, 120, 180, 240, 300, and 360 degrees x s(-1) x MMG responses were detected by a piezoelectric recording device placed over the vastus lateralis muscle. Intraclass reliability correlations ranged from R = 0.84 to 0.97 and from 0.90 to 0.99 for peak torque and MMG amplitude values, respectively, with no significant differences (P > 0.05) between the mean values for test versus retest at any contraction velocity. There were significant differences (P < 0.05) in peak torque at all velocities except 240 [135 (27) Nm] versus 300 [127 (27) Nm], and 300 versus 360 degrees x s(-1) [115 (37) Nm]. The mean MMG amplitude at 60 degrees x s(-1) [61 (67) mV] was significantly less (P < 0.05) than that at 360 degrees x s(-1) [452 (451) mV]. These results indicate a velocity-related dissociation between MMG amplitude and peak torque. Furthermore, it was hypothesized that the increases in MMG amplitude were due to velocity-related decreases in muscle stiffness which allowed for greater muscle fiber oscillations.