Isokinetics and Exercise Science - Volume 7, issue 2

Authors: Gerdle, Bjorn | Karlsson, Stefan | Crenshaw, Albert G. | Fridén, Jan | Nilsson, Lennart

Article Type: Research Article

Abstract: During dynamic (isokinetic) maximal contractions the mechanical output will decrease steeply during the initial 20--60 contractions (the fatigue phase) followed by a stable level (the endurance level). From visual inspections it is obvious that the breakpoint between these two phases differs between individuals. Based upon regression techniques we have investigated two variables of interest with respect to the breakpoint: the number of contractions (Bp-no) before the breakpoint and the angle (o ) between the …two phases (Bp-deg). We also investigated the interrelationship between output, sex, muscle morphology, and the two variables of the breakpoint during maximal dynamic knee extensions. Twenty clinically healthy subjects (11 males and 9 females) participated. Muscle biopsies of vastus lateralis were obtained from 19 out of 20 subjects. Bp-no was found at 42 ± 14 contractions (no sex difference). A significant difference p=0.001 between the two sexes was found for the Bp-deg (males: 100 pm 14 vs. females: 12 pm 16. No significant correlation existed between Bb-no and Bp-deg. Bp-deg and initial peak torque mainly correlated with the fibre areas. Bp-deg could be predicted in a model with sex and fibre areas as significant variables. The slope and endurance level (absolute and relative) of peak torque and Bp-no correlated negatively with % type 2b. Analyses of the relationship between output and morphology showed that different morphological variables (area or proportions) were of significant importance in different stages of the endurance test. In conclusion a method for determination of the breakpoint has been presented. The two variables presented correlated with important physiological aspects. Show more

Keywords: dynamic, human, knee extensors, morphology

DOI: 10.3233/IES-1998-0017

Citation: Isokinetics and Exercise Science, vol. 7, no. 2, pp. 49-60, 1998

Authors: Bellew, James W.

Article Type: Research Article

Abstract: Objective: To assess gender differences in the correlation between score on a questionnaire of self-perceived level of physical activity and rank on a test age-groups. Design: Sixty subjects in gender-age groups 20-29, 40-49, and 60-69 years of age. Each completed a self-assessment questionnaire of physical activity prior to isokinetic testing of quadriceps strength during concentric and eccentric conditions at 60 and 120 o .s-1 . Ordinal rank on both the strength test and questionnaire were …compared to determine whether self-assessment of activity correlated with rank on the strength test. Simple and multiple regression procedures were completed correlating gender, questionnaire score, and strength. Results: Gender specific results showed males rated themselves higher on the questionnaire (p = 0.02). Multiple regression revealed that questionnaire score and age were significantly correlated to rank on the strength test (p = 0.02) in males only. Simple regression failed to show significance between strength test rank and questionnaire score for either gender (p = 0.46). Similarly, no significant relationship was found between age and questionnaire score for either gender. Conclusion: Rank within gender-age group on a test of isokinetic strength may be predicted by age and total questionnaire score in male but nog females. Likewise, between gender differences exist as males consistently rate themselves more active than females. Show more

Keywords: aging, physical activity, strength, gender

DOI: 10.3233/IES-1998-0018

Citation: Isokinetics and Exercise Science, vol. 7, no. 2, pp. 61-66, 1998

Authors: McMeeken, Joan M. | Story, Ian H. | Smith, Jenni | Ken, Peter

Article Type: Research Article

Abstract: Reliability of measurement of maximum isokinetic muscle performance in subjects with rheumatoid arthritis has not been reported for the KinCom dynamometer. The aim in this study was to estimate intra and inter-session reliability in knee extensor and flexor muscles. Concentric peak torque (Nm) of knee extension and flexion at 60o .s-1 and 120o .s-1 was measured in 18 subjects (49.7 +/- 5.3 (29-76) years) with rheumatoid arthritis using a standardised protocol. Intra-session reliability (ICC …3,1) assessed in six subjects was found to be high in extensor (0.99) and flexor muscles (0.99). Comparison between left and right knees showed no statistically significant differences. Inter-session reliability (ICC 2,3) assessed over a six-week interval was also high for extensors (60o .s-1 = 0.97, 120o .s-1 = 0.97) and flexors (60o .s-1 = 0.94, 120 o .s-1 = 0.97). These findings indicate that when using a single rater, inter and intra-session reliability of knee muscle peak isokinetic concentric torque measurement are acceptable. The time interval between test sessions of six weeks reflects the clinical environment. Therefore this protocol provides a useful test for evaluation of therapeutic interventions directed at the knee. Show more

Keywords: rheumatoid arthritis, reliability, knee muscles

DOI: 10.3233/IES-1998-0019

Citation: Isokinetics and Exercise Science, vol. 7, no. 2, pp. 67-73, 1998

Authors: Hutchins, Ronald | Miller, John P. | Croce, Ronald

Article Type: Research Article

Abstract: The purpose of this study was two-fold: 1) to examine the median frequency of the electromyographic activity (mfEMG) of the quadriceps and hamstrings during isokinetic movements at 60, 180 and 300o .s-1 and 2) to examine the changes in the mfEMG with fatigue at 300o .s-1 . Fourteen female athletes had their dominant limb tested on a Cybex II+ isokinetic dynamometer (Cybex, Ronkonkoma, NY). The mfEMG of the quadriceps and hamstring muscle groups was determined …by placing bipolar surface electrodes on the vastus lateralis, vastus medialis, biceps femoris, and medial hamstrings. Repeated measures ANOVA indicated no effect of movement velocity on the mfEMG of the quadriceps. Significant differences were noted however in the mfEMG of the hamstrings with the higher movement velocities effecting significant upward shifts in the mfEMG. Significant differences were also noted in the mfEMG of both the quadriceps and the hamstrings within the 300o .s-1 trials with the mfEMG shifting downward as the muscles fatigued. These results suggest that there is a difference in motor recruitment strategies for the hamstrings between low, moderate and high speed isokinetic activity and for the quadriceps and the hamstrings during high velocity movement. Show more

Keywords: EMG, median frequency, motor unit

DOI: 10.3233/IES-1998-0020

Citation: Isokinetics and Exercise Science, vol. 7, no. 2, pp. 75-78, 1998

Authors: Iossifidou, Anna N. | Baltzopoulos, Vassilios

Article Type: Research Article

Abstract: Moment measurements in isokinetic dynamometry are influenced by moments due to acceleration. The purpose of the present study was to examine the inertial effects on peak moment, power and work during concentric isokinetic knee extension at 60, 180 and 300 deg/s. Seven healthy young adults participated in the present study. Angular displacement from the Biodex software was used to calculate angular velocity and acceleration. A recursive second-order Butterworth filter was applied on angular displacement data and …a cut-off frequency of approximately 5 Hz was used based on power spectrum assessment. Finally the actual joint moment was calculated by taking into account the moments due to acceleration of the limb-lever arm system. In general the correlations between the examined parameters were not influenced by inertial effects. A weak relationship between peak moment and power was found at 300 deg/s. Furthermore the differences between dynamometer moment and the moment corrected for the inertial effects increased as the preselected angular velocity increased. At 300 deg s the dynamometer moment was 8.12% higher than the calculated joint moment. Absolute values of work measurements were similar before and after correction but work production was different during the initial acceleration and the final deceleration periods. Based on our findings it was concluded that corrections for inertial effects are essential during moment, work and power measurements at high velocities in isokinetic dynamometry. Finally, work and power should not be replaced by peak moment because they depend on both the range of motion and the moment development throughout the range of motion and therefore offer additional information concerning muscle and joint function. Show more

Keywords: isokinetic, power, work, acceleration, moment

DOI: 10.3233/IES-1998-0022

Citation: Isokinetics and Exercise Science, vol. 7, no. 2, pp. 79-86, 1998

Authors: Iossifidou, Anna N. | Baltzopoulos, Vassilios

Article Type: Research Article

Abstract: The various isokinetic parameters are influenced by inertial moments developed during the acceleration and deceleration periods. Hence the purpose of this study was to examine inertial effects on moment versus angular displacement curves and on the angle of peak moment. Seven young adults performed 5 repetitions of concentric knee extension on the Lido isokinetic dynamometer at 30, 165 and 300 deg/s. The angular displacement and moment signals were collected and A/D converted via a 16 channel …A/D card independently from the dynamometer software. Angular displacement data were smoothed using a second order Butterworth filter. The cut-off was approximately 5 Hz and was based on power spectrum assessment. Knee joint moment was calculated taking into account the inertial effects of the limb-lever arm system. Differences on the moment versus angular displacement curves were found before and after correction for the inertial effects.These differences were limited at medium to high velocities and during the initial and final parts of the movement. Angle of peak moment uncorrected and corrected for inertial effects decreased (closer to full extension) or increased (closer to full flexion) respectively as the velocity increased. It was concluded that erroneous moment curves and angle of peak moment are obtained at high velocities when the inertial effects are ignored. Therefore it is essential at high velocities to correct for inertial effects in order to obtain valid and comparable results and hence to achieve a more accurate approach to muscle and joint function assessment using these parameters. Show more

Keywords: isokinetic, moment curve, angle of peak moment, inertia, acceleration

DOI: 10.3233/IES-1998-0021

Citation: Isokinetics and Exercise Science, vol. 7, no. 2, pp. 87-93, 1998

Authors: Burkett, Lee N. | Seminoff, Cynthia C. | Alvar, Brent A.

Article Type: Research Article

Abstract: Forty subjects (mean = 22.5 years, S.D. 2.56 years) were randomly selected who were not regularly involved in routine stretching exercises for the hamstring and low back. Subjects were compared for flexibility increase of the hamstrings and low back after a four-week training period using traditional stretching techniques and a new device, the Power Stretch. The subjects were divided randomly into three groups: (1) Group I (control 1, n = 12) which stretched with the assistance …of a Certified Athletic Trainer; (2) Group II (control 2, n = 15) which stretched with no assistance and; (3) Group III (experimental, n = 13) which stretched with the Power Stretch. Flexibility was measured (after a short warm-up) using a Wells sit-and-reach box. Long-term flexibility was assessed by comparing flexibility before the four-week intervention and after the four-week intervention. The statistical results indicated there was a significant increase in long-term flexibility or all techniques, but there was no significant difference between the techniques. This study indicated that the Power Stretch was as effective as the traditional stretching techniques used in this study. Show more

Keywords: flexibility, hamstrings, devices

DOI: 10.3233/IES-1998-0023

Citation: Isokinetics and Exercise Science, vol. 7, no. 2, pp. 95-99, 1998