Tammy K. Evetovich

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.

Mechanomyographic responses to concentric isokinetic muscle contractions

Abstract 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° · s−1. 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° · s−1 [115 (37) Nm]. The mean MMG amplitude at 60° · s−1 [61 (67) mV] was significantly less (P < 0.05) than that at 360° · 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.

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°, 90°, and 150° 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.

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.

Mechanomyography and oxygen consumption during incremental cycle ergometry.

Abstract The purpose of this investigation was to describe and compare the relationships for mechanomyography (MMG) and oxygen consumption rate (V˙O2) versus power output during incremental cycle ergometry. Twenty four adult males [mean (SD) age, 22.1 (2.0) years] volunteered to perform an incremental test to exhaustion on a cycle ergometer. A MMG piezoelectric recording device was placed mid-thigh over the vastus lateralis muscle and V˙O2 was measured using standard open circuit procedures. The r2 values for the MMG and V˙O2 versus power output relationships ranged from 0.79 to 0.99 and 0.97 to 0.99, respectively. In 20 of the 24 subjects there was no significant (P > 0.10) difference between the slope values for the normalized MMG and V˙O2 (expressed as a percentage of maximal values) versus power output relationships. The results of this study indicate that MMG procedures can be used to quantify muscular activity and monitor changes in exercise intensity during cycle ergometry. Furthermore, the present findings demonstrated a close association between the mechanical (MMG) and metabolic (V˙O2) aspects of muscular contraction during incremental cycle ergometry.

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°s−1. All subjects were tested every 4 weeks for PT and EMG responses of both legs at a velocity of 90°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 xtension.

Effect of moderate dehydration on torque, electromyography, and mechanomyography

The purpose of the present investigation was to test the hypotheses that the mechanomyographic (MMG) signal would be affected by hydration status due to changes in the intra‐ and extracellular fluid content (which could affect the degree of fluid turbulence), changes in the filtering properties of the tissues between the MMG sensor and muscle, and changes in torque production that may accompany dehydration. Ten subjects (age 22.5 ± 1.6 years) were tested for maximal isometric (MVC), submaximal isometric (25, 50, and 75%MVC), and maximal concentric isokinetic muscle strength of the biceps brachii in either a euhydrated or dehydrated state while the electromyographic (EMG) and MMG signals were recorded. Separate three‐way and two‐way ANOVAs indicated no change in torque, EMG amplitude, EMG mean power frequency (MPF), MMG amplitude, and MMG MPF with dehydration. The lack of dehydration effect suggests that MMG may be more reflective of the intrinsic contractile processes of a muscle fiber (torque production) or the motor control mechanisms (reflected by the EMG) than the tissues and fluids surrounding the muscle fiber.

Electromyographic fatigue thresholds of the superficial muscles of the quadriceps femoris

The purpose of this investigation was to compare the thresholds of neuromuscular fatigue determined simultaneously from the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles using the electromyographic fatigue threshold (EMGFT) test, Eight adult volunteers [mean (SD) age, 33 (10) years] served as subjects for this investigation. The results of a one-way repeated measured ANOVA indicated that there was a significant (P < 0.05) difference among the mean EMGFT values for the VL [248(31)W], VM [223(43)W] and RF [220(30)W] muscles. Tukey post-hoc comparisons indicated that the EMGFT for the RF was significantly (P < 0.05) lower than that of the VL. These findings suggested that during cycle ergometry there is a dissociation in neuromuscular fatigue characteristics of the superficial muscles of the quadriceps femoris group.

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

Abstract 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° below full extension. A piezoelectric MMG recording device was placed over the mid-portion of the rectus femoris. At 25° of leg flexion, the MMG amplitude increased to 100%MVC. At 50 and 75° 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.

Effects of Low- and High-Volume Stretching on Bench Press Performance in Collegiate Football Players

Molacek, ZD, Conley, DS, Evetovich, TK, and Hinnerichs, KR. Bench press performance in collegiate football players. J Strength Cond Res 24(3): 711-716, 2010-The purpose of this study was to determine the effects of acute low- and high-volume static and proprioceptive neuromuscular facilitation (PNF) stretching on 1-repetition maximum (1RM) bench press. Fifteen healthy male National Collegiate Athletic Association Division II football players (age: 19.9 ± 1.1 years; weight: 98.89 ± 13.39 kg; height: 184.2 ± 5.7 cm; body composition: 14.6 ± 7.4%; and 1RM bench press: 129.7 ± 3.3 kg) volunteered to participate in the study. Subjects completed 5 different stretching protocols integrated with a 1RM dynamic warm-up routine followed by 1RM testing in randomly assigned order. The protocols included (a) nonstretching (NS), (b) low-volume PNF stretching (LVPNFS), (c) high-volume PNF stretching (HVPNFS), (d) low-volume static stretching (LVSS), and (d) high-volume static stretching (HVSS). Two and 5 sets of stretching were completed for the low- and high-volume protocols, respectively. The stretching protocols targeted triceps and chest/shoulder muscle groups using 2 separate exercises. There were no significant differences in 1RM bench press performance (p > 0.05) among any of the stretching protocols NS (129.7 ± 3.3 kg), LVPNFS (128.9 ± 3.8 kg), HVPNFS (128.3 ± 3.7 kg), LVSS (129.7 ± 3.7 kg), and HVSS (128.2 ± 3.7 kg). We conclude that low- and high-volume PNF and static stretching have no significant acute effect on 1RM bench press in resistance-trained collegiate football players. This suggests that resistance-trained athletes can include either (a) a dynamic warm-up with no stretching or (b) a dynamic warm-up in concert with low- or high-volume static or PNF flexibility exercises before maximal upper body isotonic resistance-training lifts, if adequate rest is allowed before performance.