Biomedical subjects

Danny M Pincivero

Publications and source records attributed to Danny M Pincivero.

13 recordsLinked to original sources

PubMed2006

Quadriceps femoris electromyogram during concentric, isometric and eccentric phases of fatiguing dynamic knee extensions.

The objective of this study was to examine the superficial quadriceps femoris (QF) muscle electromyogram (EMG) during fatiguing knee extensions. Thirty young adults were evaluated for their one-repetition maximum (1RM) during a seated, right-leg, inertial knee extension. All subjects then completed a single set of repeated knee extensions at 50% 1RM, to failure. Subjects performed a knee extension (concentric phase), held the weight with the knee extended for 2s (isometric phase), and lowered the weight in a controlled manner (eccentric phase). Raw EMG of the vastus medialis (VM), vastus lateralis (VL) and rectus femoris (RF) muscles were full-wave rectified, integrated and normalized to the 1RM EMG, for each respective phase and repetition. The EMG median frequency (f(med)) was computed during the isometric phase. An increase in QF muscle EMG was observed during the concentric phase across the exercise duration. VL EMG was greater than the VM and RF muscles during the isometric phase, in which no significant changes occurred in any of the muscles across the exercise duration. A significant decrease in EMG across the exercise duration was observed during the eccentric phase, with the VL EMG greater than the VM and RF muscles. A greater decrease in VL and RF muscle f(med) during the isometric phase, than the VM muscle, was observed with no gender differences. The findings demonstrated differential recruitment of the superficial QF muscle, depending on the contraction mode during dynamic knee extension exercise, where VL muscle dominance appears to manifest across the concentric-isometric-eccentric transition.

Adaptation, Physiological↗

PubMed2006

Relationship between hip and knee strength and knee valgus during a single leg squat.

The purpose of this study was to determine the relationship between hip and knee strength, and valgus knee motion during a single leg squat. Thirty healthy adults (15 men, 15 women) stood on their preferred foot, squatted to approximately 60 deg of knee flexion, and returned to the standing position. Frontal plane knee motion was evaluated using 3-D motion analysis. During Session 2, isokinetic (60 deg/sec) concentric and eccentric hip (abduction/adduction, flexion/extension, and internal/external rotation) and knee (flexion/extension) strength was evaluated. The results demonstrated that hip abduction (r2=0.13), knee flexion (r2=0.18), and knee extension (r2=0.14) peak torque were significant predictors of frontal plane knee motion. Significant negative correlations showed that individuals with greater hip abduction (r=-0.37), knee flexion (r=-0.43), and knee extension (r=-0.37) peak torque exhibited less motion toward the valgus direction. Men exhibited significantly greater absolute peak torque for all motions, excluding eccentric internal rotation. When normalized to body mass, men demonstrated significantly greater strength than women for concentric hip adduction and flexion, knee flexion and extension, and eccentric hip extension. The major findings demonstrate a significant role of hip muscle strength in the control of frontal plane knee motion.

Adult↗

PubMed2004

Angle- and gender-specific quadriceps femoris muscle recruitment and knee extensor torque.

The objectives were to examine knee angle-, and gender-specific knee extensor torque output and quadriceps femoris (QF) muscle recruitment during maximal effort, voluntary contractions. Fourteen young adult men and 15 young adult women performed three isometric maximal voluntary contractions (MVC), in a random order, with the knee at 0 degrees (terminal extension), 10 degrees, 30 degrees, 50 degrees, 70 degrees, and 90 degrees flexion. Knee extensor peak torque (PT), and average torque (AT) were expressed in absolute (N m), relative (N m kg(-1)) and allometric-modeled (N m kg(-n)) units. Vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscle EMG signals were full-wave rectified and integrated over the middle 3 s of each contraction, averaged over the three trials at each knee angle, and normalized to the activity recorded at 0 degrees. Muscle recruitment efficiency was calculated as the ratio of the normalized EMG of each muscle to the allometric-modeled average torque (normalized to the values at 0 degrees flexion), and expressed as a percent. Men generated significantly greater knee extensor PT and AT than women in absolute, relative and allometric-modeled units. Absolute and relative PT and AT were significantly highest at 70 degrees, while allometric-modeled values were observed to increase significantly across knee joint angles 10-90 degrees. VM EMG was significantly greater than the VL and RF muscles across all angles, and followed a similar pattern to absolute knee extensor torque. Recruitment efficiency improved across knee joint angles 10-90 degrees and was highest for the VL muscle. VM recruitment efficiency improved more than the VL and RF muscles across 70-90 degrees flexion. The findings demonstrate angle-, and gender-specific responses of knee extensor torque to maximal-effort contractions, while superficial QF muscle recruitment was most efficient at 90 degrees, and less dependent on gender.

Adult↗

PubMed2004

Gender differences in perceived exertion during fatiguing knee extensions.

PURPOSE: To examine gender differences in knee extensor strength, fatigue, and perceived exertion during a single set of continuous dynamic knee extensor contractions. METHODS: Fifteen men and 15 women were evaluated for their one-repetition maximum (1RM) during a single-leg, inertial knee extension with their right leg. All subjects then completed a single set of repeated knee extensions with a load equivalent to 50% of their 1RM to failure. Subjects lifted the weight by performing a knee extension, held the weight with the knee extended for 1-2 s, and then lowered the weight in a slow and controlled manner. Perceived exertion was measured after completion of each repetition, by viewing a modified Borg category-ratio (CR-10) scale. Perceived exertion responses were standardized across subjects via linear interpolation and power function modeling. The linear interpolated perceived exertion estimates were then examined for linear, quadratic, and cubic trends across the repetitions. RESULTS: Men lifted a significantly greater amount of mass than women, when corrected for body mass. Men and women did not differ significantly in the number of repetitions performed to failure. Women displayed significantly higher power function exponents for the perceived exertion response than men (0.72 +/- 0.16 and 0.57 +/- 0.16, respectively) and demonstrated statistically nonsignificant greater increases in perceived exertion than men across the repetitions. CONCLUSIONS: The major findings of this study indicated that: 1) men inherently possessed greater knee extensor strength than women; 2) submaximal fatiguing knee extensor performance did not differ between genders; 3) model selection had a significant impact on standardizing perceived exertion estimates; and 4) subtle gender differences in the perceived exertion response may have existed during submaximal, fatiguing resistance exercise.

Adult↗

PubMed2004

The effects of rest interval length on ratings of perceived exertion during dynamic knee extension exercise.

The objective of this study was to examine the effects of rest interval length on perceived exertion and during 3 sets of 10 inertial knee extension repetitions. Thirty healthy men (n = 15) and women (n = 15) volunteers were randomly assigned to 1 of 3 groups (1-, 2-, or 3-minute rest interval length) following the establishment of each subject's 1 repetition maximum (1RM) for inertial knee extension exercise. Subjects in each group performed 3 sets of 10 repetitions at 70% of a theoretical 10RM (based on each subject's 1RM), with a 1-, 2-, or 3-minute rest interval between each set. Perceived exertion was recorded, via the Borg category-ratio scale, from each subject after each repetition of each set. The results demonstrated no significant rest interval length effect on perceived exertion across the 3 sets of 10 repetitions. The results revealed a significantly higher perceived exertion value following the first repetition in set 3 as compared to sets 2 and 1 in all groups. The increase in perceived exertion within each set, as described by the slope, was found to be significantly lowest in set 1, as compared to sets 2 and 3. The major findings of this study demonstrate that perceived exertion significantly increases in a similar manner across 3 sets of 10 knee extension repetitions, despite rest interval lengths of 1-3 minutes.

Adult↗

PubMed2003

Perceived exertion and maximal quadriceps femoris muscle strength during dynamic knee extension exercise in young adult males and females.

The objectives of the present study were to: (1) examine perceived exertion across different target voluntary-contraction intensities; (2) compare perceived exertion ratings with actual target intensities, and (3) compare perceived exertion ratings between males and females. Subjects for this study included 30 healthy, college-aged male (n=15) and female (n=15) volunteers. All subjects were free of orthopedic, cardiopulmonary, systemic and neurological disease. Subjects were evaluated for their one-repetition maximum (1-RM) during inertial knee extension exercise. All subjects then completed, in a random order, two sub-maximal inertial contractions at 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% of their 1-RM. Perceived exertion was measured by asking subjects to provide a number that corresponded to the feelings in their quadriceps after completion of the two repetitions, by viewing a modified category-ratio (CR-10) scale. The results showed that males lifted a significantly greater absolute (P<0.05) and relative (P<0.05) amount of mass than females; allometric-modeled strength values also demonstrated significant sex differences. The results revealed a significant intensity main effect (P<0.001) but no significant gender main effect (P=0.97) nor intensity-by-gender interactions (P=0.50) for the perceived exertion responses. The findings demonstrated that perceived exertion was significantly (P<0.05) lower than the specific expected values on the CR-10 scale from 10% to 60% of 1-RM, but was not different from 70% to 90% 1-RM. The results revealed that the increase in perceived exertion was fit to both linear and quadratic trends, and that the exponent of the power function was found to be 1.437 (SD 0.22) for the males, and 1.497 (0.295) for the females. The major findings demonstrate that although males were able to lift more absolute and relative mass than females, the perceptual response to relative load was similar between genders. The increase in perceived exertion, as a function of relative load, showed a strong linear trend; however, enhanced perceptual sensitivity at high contraction intensities was evident from the positively accelerating power function.

Adult↗

PubMed2003

Gender-specific knee extensor torque, flexor torque, and muscle fatigue responses during maximal effort contractions.

The purpose of this study was to examine gender differences in knee extensor and flexor peak torque, work, power, and muscle fatigue during maximal effort isokinetic contractions. Subjects included 19 healthy male and 20 healthy female volunteers. Following a dynamic warm-up period, subjects performed 30 reciprocal, concentric maximal knee extension and flexion contractions at a pre-set angular velocity of 3.14 rad x s(-1) on the Biodex Isokinetic Dynamometer. Values for knee extensor peak torque, work, and power were calculated for each repetition over an angular displacement of 1.05 rad for each repetition. The single highest repetition value for knee extensor and flexor peak torque, work, and power was then calculated relative to body mass (N x m x kg(-1), J x kg(-1), W x kg(-1)) and allometric-scaled (N x m x kg(-) (n), J x kg(-) (n), W x kg(-) (n)) units. The allometric-scaled units were derived from a log-log transformation and linear regression analysis to calculate the exponent to which body mass is raised. The rate of quadriceps femoris muscle fatigue was calculated as the decline in each isokinetic variable by the linear slope from the single highest repetition value through the 30th repetition, and by two different fatigue indexes. The results demonstrate higher knee extension and flexion peak torque, work, and power in absolute, relative, and allometric-scaled units for males compared to females. Males exhibited higher fatigue rates for both muscle groups of each isokinetic variable than females, as described by the slope and the fatigue index, except when adjusted for peak values via analysis of covariance. The findings suggest that during maximal-effort muscle contractions, males exhibit a higher susceptibility to muscle fatigue than females, a phenomenon that may be related to an inherent ability to generate higher knee extensor and flexor torque.

Adult↗

PubMed2003

Knee extensor torque, work, and EMG during subjectively graded dynamic contractions.

We examined knee extensor peak torque, work, and electromyogram (EMG) during dynamic contractions to perceived exertion levels in men and women. Thirty subjects performed three maximal effort isokinetic knee extensions (60 deg x s(-1)), followed by three contractions to each of nine separate levels of perceived exertion. Surface EMG of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF), and knee extensor peak torque and work were normalized to a percent of each respective value obtained during the maximal effort contractions. The results demonstrated a significant linear increase in voluntary knee extensor peak torque and work across perceived exertion levels. Knee extensor peak torque and work were less than 70%, 80%, and 90% maximal voluntary contraction (MVC) at perceived exertion levels 7, 8, and 9, respectively. A significant increase in VM, VL, and RF muscle EMG was observed across perceived exertion levels 1 through 9, with EMG increase highest for the VL. The findings demonstrate that dynamic contractions guided by perceived exertion are underproduced at relatively high perceptual intensities, and that reliance on VL activation occurs across submaximal torque levels. The overestimation of knee extensor peak torque and work at relatively high perceptual intensities may suggest the presence of a subconscious mechanism aiming to reduce high muscle and joint forces.

Adult↗

PubMed2003

The effects of acute stretching on hamstring muscle fatigue and perceived exertion.

The aim of this study was to examine the effects of an acute stretching regime on hamstring muscle fatigue and rating of perceived exertion during a dynamic, sub-maximal bout of resistance exercise. Sixteen healthy males (age 25.7 +/- 4.3 years, height 1.81 +/- 0.06 m, body mass 87.5 +/- 15.1 kg; mean +/- s) and 16 healthy females (age 24.9 +/- 4.5 years, height 1.67 +/- 0.06 m, body mass 62.9 +/- 9.4 kg) volunteered to participate in two experimental sessions. After establishing their one-repetition maximum for the hamstring curl, the participants were assigned at random to one of two groups. Group 1 performed three bouts of 20 s hamstring stretches with the assistance of one of the investigators, while group 2 did not perform the stretches; instead, they sat resting for 3 min. Then, after stretching or resting, the participants performed as many hamstring curls as they could at 60% of their one-repetition maximum established earlier. All participants were assessed for their perceived exertion using a modified Borg category ratio (CR-10) scale. The participants returned within 1 week to complete the experiment. This time group 1 did not perform hamstring stretches, whereas group 2 did. As on the first occasion, all participants performed hamstring curls after stretching or resting. The participants in group 1 were able to perform more curls on the second day of testing than their counterparts in group 2. There were no significant differences between males and females or between the stretch and non-stretch conditions. There was a significantly higher first repetition rating of perceived exertion for the stretch condition (2.88 +/- 1.01) than for the non-stretch condition (2.50 +/- 0.95); there was no significant difference in the median ratings of perceived exertion between the stretch and non-stretch conditions. Significantly higher power function exponents were exhibited in the non-stretch (0.57 +/- 0.16) than in the stretch condition (0.51 +/- 0.12). In addition, females exhibited significantly higher power function exponents than males, irrespective of stretch condition and day (females: 0.59 +/- 0.12; males: 0.49 +/- 0.11). In conclusion, we found a small but statistically significant effect of an acute bout of stretching on ratings of perceived exertion during fatiguing hamstring muscle resistance exercise.

Adult↗

PubMed2003

Knee flexor torque and perceived exertion: a gender and reliability analysis.

PURPOSE: The objectives of the present study were to examine gender differences and between-day variability of isometric hamstring muscle peak torque and perceived exertion. METHODS: Subjects included 20 healthy, college-aged male (N = 10) and female (N = 10) volunteers. Each subject completed five maximal voluntary isometric hamstring muscle contractions (MVC), in a prone position, with their knee at 30 degrees flexion. Subjects then completed, in random order, isometric contractions at 10, 20, 30, 40, 50, 60, 70, 80, and 90% of their three highest averaged MVC. Perceived exertion was measured with a modified Borg CR-10 scale after each contraction. Ten randomly chosen subjects were asked to return approximately 1 wk after the initial evaluation to repeat the same procedure. Peak hamstring muscle torque was examined in absolute (N.m), relative (N.m.kg-1), and allometric-scaled (N.m.kg-n) units. Perceived exertion across the contraction intensities was modeled to a power function in order to determine the exponent and proportionality constant. RESULTS: Males generated significantly greater hamstring muscle torque than females in absolute, relative, and allometric-scaled units (P < 0.05). No significant differences in perceived exertion occurred across the submaximal contraction intensities between females and males, nor for the derived exponents and proportionality constants. Perceived exertion ratings were observed to be significantly lower (P < 0.05) across the contraction intensity range on the second day. CONCLUSIONS: The major findings demonstrated that perceived exertion did not differ between healthy young female and male adults, despite males generating significantly more hamstring muscle torque, and perceived exertion ratings decreased at similar relative contraction intensity levels across testing days.

Adult↗

PubMed2002

The effects of voluntary contraction effort on quadriceps femoris electromyogram median frequency in humans: a muscle and sex comparison.

The purpose of this study was to examine the effect of voluntary contraction efforts on the median frequency (f(med)) of the electromyogram (EMG) recorded from the quadriceps femoris muscle in healthy men and women. A group of 30 healthy volunteers (15 men, 15 women) were assessed for EMG activity of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscles during isometric contractions with the knee at 60 degrees flexion. Subjects performed a series of 5 s maximal voluntary isometric contractions that anchored the perceptual range with a "10" on a 10-point scale. Sub-maximal isometric contractions were then separately performed at the following perceived effort levels on the 10-point scale: 1, 2, 3, 4, 5, 6, 7, 8 and 9, in a random order. Subjects were instructed to maintain the contraction at each perceived level of effort for 5 s. The f(med) of the three muscles was assessed using a power spectrum analysis performed over 11 consecutive, 512 ms, epochs overlapping each other by half their length during the middle 3 s of each contraction. The f(med) for each of the 11 epochs was then determined for each muscle, followed by calculation of the means and normalized coefficients of variation [(standard deviation/mean)x100%] for each contraction. The results demonstrated that the mean f(med) of VL was significantly greater than those of the other two muscles, and that f(med) of RF was significantly greater than that of VM. The VL muscle demonstrated a significant increase in mean f(med) across the contraction efforts, compared to the VM and RF muscles that displayed a significant decrease. The men displayed significantly higher f(med) values for the VM muscle than did the women, as well as showing a significantly greater increase across the contraction efforts for the VL muscle. The variability of f(med) was shown to be significantly higher for the VM muscle, compared to the VL and RF muscles. The findings of this study suggest that the f(med) statistic is most sensitive to contraction intensity efforts for the VL muscle, and that men display significantly higher values for the VL and VM muscles, compared to women.

Adult↗

PubMed2002

The effects of ACL injury on quadriceps and hamstring torque, work and power.

The aim of this study was to assess isokinetic torque, work and power between non-injured, ACL (anterior cruciate ligament)-deficient and ACL-reconstructed individuals. Ten healthy, non-injured individuals, seven unilateral ACL-deficient individuals and six unilateral ACL-reconstructed individuals were assessed for isokinetic quadriceps and hamstring strength at 1.05 and 3.14 rad.s-1. Peak torque, total work, average power and the ratio of peak torque to body mass were computed for both velocities. Peak torque was also corrected for body mass, using allometric modelling. The non-injured individuals showed significantly greater quadriceps peak torque to body mass ratios than the ACL-deficient and ACL-reconstructed individuals at both velocities, and greater hamstring peak torque to body mass ratios than the ACL-deficient group at 3.14 rad.s-1 (P < 0.05). The ACL-deficient individuals displayed greater quadriceps and hamstring peak torque, total work and average power than the non-injured individuals at 1.05 rad.s-1 (P < 0.05). The ACL-deficient individuals also displayed significantly greater peak torque, total work and average power than the ACL-reconstructed individuals for the quadriceps at both velocities (P < 0.05). The ACL-deficient individuals demonstrated greater hamstring peak torque and total work than the non-injured individuals at both velocities (P < 0.05). The allometrically modelled peak torques at both isokinetic velocities demonstrated that the quadriceps muscle values were significantly higher in the non-involved than the involved limb. The hamstring peak torques corrected for body mass were significantly higher in the non-involved than the involved limb only at 1.05 rad.s-1. The main finding from the present study is that isokinetic measures in ratio-scaled or absolute units yield a different outcome and, hence, interpretation compared with the allometric approach.

Adult↗

PubMed2002

The effects of cold-water immersion on power output and heart rate in elite cyclists.

The purpose of this study was to examine the effects of cold-water immersion on power output, heart rate, and time to peak power in 10 well-trained cyclists. The Compu-trainer Professional Model 8001 computerized stationary trainer was used to evaluate maximum power, average power, and time to peak power during a simulated cycling sprint. The heart rate was measured using a Polar heart rate monitor. Subjects performed 2 maximum-effort sprints (for approximately 30 seconds) separated by either an experimental condition (15 minutes of cold-water immersion at 12 degrees C up to the level of the iliac crest) or a control condition (15 minutes of quiet sitting). All subjects participated under both control and experimental conditions in a counterbalanced design in which 5 subjects performed the experimental condition first and the other 5 subjects performed the control condition first. Each condition was separated by at least 2 days. The time to peak power was not different between the 2 conditions. Maximum and average powers declined by 13.7 and 9.5% for the experimental condition but only by 4.7 and 2.3% for the control condition, respectively. The results also demonstrated a significantly greater decline in maximum heart rate after cold-water immersion (8.1%) than under the control condition (2.4%). Average heart rate showed a decrease of 4.2% under the experimental condition, as compared with an increase of 1.5% under the control condition. The major findings of this study suggest that a relatively brief period of cold-water immersion can manifest significant physiological effects that can impair cycling performance.

Adult↗