Biomedical subjects

T P Mayhew

Publications and source records attributed to T P Mayhew.

10 recordsLinked to original sources

PubMed1998

Reproducibility of electromyographic recordings of submaximal concentric and eccentric muscle contractions in humans.

OBJECTIVES: to determine the intratester and intertester reliability of measures of electromyographic activity (EMG) of submaximal concentric and eccentric contractions and to compare the reliability of normalized and non-normalized measures of EMG. There were 10 subjects, of 22-33 years old. METHODS: Subjects performed submaximal concentric and eccentric contractions at 60 degrees/s, and maximal isometric contractions (MIC) of their knee extensors. The target power of the submaximal contractions was 90%+/-10% of the subject's maximal concentric power. EMG was recorded via bipolar surface electrodes from 3 of the quadriceps femoris muscles. The rmsEMG for submaximal contractions that were within the target power range were determined. The rmsEMG for the submaximal contractions were normalized to the rmsEMG of the maximal isometric contractions. Intraclass correlation coefficients (ICC version 1.1) were calculated to determine intratester and intertester reliability. RESULTS: For non-normalized rmsEMG, ICC values for intratester reliability ranged from 0.62 to 0.91 for concentric and from 0.84 to 0.97 for eccentric contractions. ICC values for intertester reliability ranged from 0.66 to 0.96 for concentric and 0.78 to 0.90 for eccentric contractions. CONCLUSIONS: Non-normalized rmsEMG of submaximal concentric and eccentric isokinetic contractions were found to be reliable. Normalization did not lead to consistently improved reliability.

Adult↗

PubMed1996

Concentric and eccentric force-velocity relationships during electrically induced submaximal contractions.

The purpose of this investigation was to examine the force-velocity relationship during electrically induced, submaximal concentric and eccentric contractions of the quadriceps femoris muscle. Thirty female subjects with no history of knee pathology participated in the study. Force was measured on an isokinetic dynamometer and the quadriceps femoris muscle was electrically stimulated by use of a medium frequency current generator. Subjects were stimulated at 30% of their maximum voluntary isometric force. Four velocities were tested (30 degrees, 90 degrees, 120 degrees and 180 degrees/sec) during both concentric and eccentric contractions. The relationship between force and velocity was examined with an analysis of covariance. The regression model describing the force-velocity relationship for concentric contractions was significant (p < 0.0001) with an R2 of 0.96 and a slope of -0.76 (p < 0.0001). The regression model describing the force-velocity relationship for eccentric contractions was significant (p < 0.0001) with an R2 of 0.91 and a slope of 0.4 (p < 0.0001). The relationship between force and velocity during electrically induced, submaximal concentric and eccentric contractions were similar to in vitro studies that have examined this relationship during shortening and lengthening contractions.

Adult↗

PubMed1996

Treatment categories for low back pain: a methodological approach.

Studies that evaluate effectiveness of physical therapy can be problematic because frequently several treatment techniques are used during an episode of care. Methods that categorize treatment techniques into discrete categories may be useful in studying treatment outcomes. The purpose of this study was to describe a method to create treatment categories used for patients with low back pain. We surveyed physical therapists in Virginia to identify frequently used treatments for patients with low back pain. One hundred fifty-five surveys were completed. Twenty-eight treatments, used frequently or very frequently by 50% or more of the respondents, were retained for analysis. Factor analysis was used to identify treatment categories. Seven categories were identified: McKenzie approach, manual therapy, exercise with equipment, active and stretching exercise, physical agents, aerobic exercise and walking, and ergonomic activities. Indices for the categories were created. Confirmatory factor analyses should be performed on a different sample to validate these findings.

Humans↗

PubMed1995

Muscular adaptation to concentric and eccentric exercise at equal power levels.

The effect of training with concentric and eccentric contractions on fiber hypertrophy and isometric torque production was investigated in 20 healthy subjects. One group (eight female and two male subjects) performed concentric contractions of their quadriceps femoris muscles at an intensity of 90% of their maximal concentric power. The other group (six female and four male subjects) performed eccentric contractions at the same relative power level. Both groups exercised three times per week for 4 wk at a constant speed of 60 degrees.s-1 on a Kin-Com dynamometer. Needle biopsies were obtained from the vastus lateralis before and after the exercise program. Fiber-type differentiation was performed using a myosin ATPase stain at a preincubation of 10.5. Maximal isometric knee extension torque was also measured before and after the exercise program. An analysis of covariance was used to determine whether there were significant differences between the exercise groups in: 1) the post-exercise fiber areas and 2) maximal isometric torque (MIso), while controlling for initial differences. Results showed a significant difference between the Type II fiber areas (P < 0.01) and the MIso (P = 0.01). These data indicate that, when exercising at the same relative power level, a subject performing concentric contractions will show greater muscle hypertrophy and improve in MIso production more than a subject training with eccentric contractions.

Adaptation, Physiological↗

PubMed1994

Performance characteristics of the Kin-Com dynamometer.

BACKGROUND AND PURPOSE: The purpose of this study was to assess the performance characteristics of a Kin-Com dynamometer (model #500-11) under controlled conditions. METHODS: Comparisons were made between measurements of force, angle, and velocity obtained from the Kin-Com and measurements acquired from an external recording system of known weights, angles, and user-set velocities. The strength of the linear relationships between measurements obtained with the different recording systems was analyzed using a coefficient of determination (r2). An intraclass correlation coefficient (ICC[2,1]) was used to examine the reliability of the force, angle, and velocity measurements obtained with each recording system on 2 different days. RESULTS: In all conditions, the coefficient of determination for the force, angle, and velocity comparisons was above .99. The ICC for between-day comparisons for all force, angle, and velocity measurements was above .99. CONCLUSION AND DISCUSSION: Our results indicate that the static measurements of force and angle that are necessary for use in the gravity-correction procedure and isometric testing are accurate and replicable between days. The Kin-Com dynamometer's control system regulating lever arm velocity is also accurate and replicable under a no-load condition. It was ascertained during the velocity testing that the use of any acceleration and deceleration mode other than "high" resulted in a loss of excursion of the lever arm.

Acceleration↗

PubMed1994

Evaluation of the gravity-correction feature of a Kin-Com isokinetic dynamometer.

BACKGROUND AND PURPOSE: Torques reflecting muscle performance must be corrected for the effects of gravity if error-free ratio-scaled data are to be obtained. Ratio-scaled data are necessary, for example, to report muscle performance characteristics in terms of ratios or percentages or in the form of ratios with another muscle (eg, ratio of hamstring to quadriceps femoris muscle peak torque). The purpose of this study was to determine the error associated with the gravity-correction procedure of the Kin-Com dynamometer when a weight or limb segment is weighed at different lever arm positions. METHODS: A known weight was suspended from the lever arm of the Kin-Com dynamometer. The rotational component of gravitational forces on the weight was measured at 11 different angular positions. We compared the force measurement obtained from the Kin-Com with the predicted rotational component at each angular position. The gravitational forces on a subject's limb segment (leg) were then measured at 12 different angular positions in each of two trunk positions (sitting and supine). We compared the force measurement obtained from the Kin-Com with the predicted rotational component for each position. Forces measured for the two trunk positions with the lever arm horizontal were compared. Forces measured with the knee extended were compared with forces measured with the lever arm horizontal. RESULTS: The dynamometer accurately recorded the rotational component of gravitational forces for the weight suspended from the lever arm. There was a progressively greater discrepancy between measured forces and predicted forces for the leg as the lever arm was moved from horizontal to 50 degrees below the horizontal. The force recorded with the Kin-Com was greater when the subject's knee was in full extension than when the lever arm was horizontal, which placed the subject's knee in a flexed position. A small difference was noted between the measured forces with the lever arm horizontal when the subject was sitting compared with when the subject was positioned supine. CONCLUSION AND DISCUSSION: When weighing a leg with this dynamometer, we recommend that the lever arm be as close to the horizontal position as possible. Positions of proximal joints should be chosen that do not put two joint muscles in stretched positions.

Adult↗

PubMed1992

Intertester reliability of judgments of the presence of trigger points in patients with low back pain.

The purpose of this study was to determine the intertester reliability of assessments of the presence of trigger points in the region of the lumbar spine of patients with low back pain (LBP). A total of six trigger points described by Travell and Simons were studied. The trigger point examination procedures described by Travell and Simons were used by 12 physical therapists. Randomly paired therapists examined 50 patients for 197 trigger points. The Kappa coefficient, percent agreement, the observed proportion of positive agreement (Ppos), and the observed proportion of negative agreement (Pneg) were used to describe reliability. Kappa values ranged from .29 to .38. Percent agreement ranged from 76% to 79%. Ppos ranged from .43 to .52. The low Kappa and Ppos values suggest different therapists are unable to reliably determine when a trigger point is present in a patient with LBP. This study suggests the usefulness of examining for the presence of trigger points in patients with LBP should be questioned.

Adult↗

PubMed1991

Exercise-induced muscle soreness after concentric and eccentric isokinetic contractions.

The purpose of this two-part study was to determine whether the amount of exercise-induced muscle soreness differs between subjects who perform concentric and eccentric isokinetic contractions of their quadriceps femoris muscles. In experiment 1, subjects were randomly assigned to either an eccentric or a concentric exercise group and both groups exercised at the same power level. In experiment 2, subjects were randomly assigned to either an eccentric or a concentric exercise group and both groups exercised with maximal effort. Muscle soreness ratings, obtained by using a visual analogue scale, were taken immediately before exercise and at 24 and 48 hours postexercise. Changes in muscle soreness ratings between exercise groups from preexercise to postexercise periods were compared in both experiments, using a one-way between-subjects analysis of variance. There was no difference in the change in muscle soreness from preexercise to post-exercise periods between groups exercising at equal power levels. Subjects who exercised using eccentric contractions with maximal effort demonstrated greater increases in muscle soreness than those who performed concentric contractions. The results suggest that exercise intensity, rather than contraction type, may be the dependent factor in producing exercise-induced muscle soreness.

Adult↗

PubMed1987

Clinical uses of isokinetic measurements. Critical issues.

Isokinetic measurements are widely used by physical therapists for evaluation and treatment planning. We believe that some use of isokinetic measurements is unwarranted in view of the paucity of credible scientific research on these measurements. With increased emphasis from third-party payers and from the medical community for documentation of the effectiveness of physical therapy services, we believe that therapists must be aware how they can and cannot use isokinetic measurements in their clinical settings. Concepts that relate to isokinetic testing are discussed and critically examined.

Humans↗

PubMed1983

Electromyographic study of the relationship between hamstring and abdominal muscles during a unilateral straight leg raise.

The purposes of this study were 1) to assess the relative participation of the hip extensor and abdominal musculature during unilateral straight leg raising in the naive subject and 2) to examine quantitatively alterations in the pattern of pelvic stabilization when the subject was instructed to relax the contralateral extremity. Surface electrodes were used to record bilaterally the electromyographic activity of the rectus abdominus, external oblique, and medial hamstring muscles. Each healthy subject performed a unilateral straight leg raise three times in each of two modes, Preferred and Relaxed. The electromyographic values for each muscle were normalized to a maximum isometric contraction and analyzed using a three-factor (2 X 2 X 2) mixed design analysis of variance. Results indicate that 9 of the 11 subjects used the tested medial hamstrings and abdominal muscles during a unilateral straight leg raise performed in the Preferred Mode. When instructed to relax the contralateral extremity for the Relaxed Mode, abdominal muscle activity increased significantly (p less than .01). The findings indicate that although most subjects normally stabilize with the contralateral extremity during a unilateral straight leg raise, they can consciously alter the pattern.

Abdominal Muscles↗