Isokinetics and Exercise Science

Previous studies have proposed that thigh muscle imbalance is a critical risk factor for the athletic non-contact knee injuries. However, there is a little consensus among prospective studies with regard to the correlation between isokinetic hamstring to quadriceps strength ratio (HQR) and the non-contact knee injury rates. Most of athletic movements at risk are closed kinetic chain movements, and compensatory effect among ankle, knee, and hip joints during the closed kinetic chain movement was observed in the previous literatures. Therefore, it is assumed that hamstrings and quadriceps (H:Q) imbalance can cause non-contact lower extremity injuries without necessarily causing knee injuries. The purpose of this study was to prospectively investigate the relationship between H:Q strength imbalance and overall non-contact lower extremity injuries. A prospective cohort study was conducted on NCAA division III basketball and soccer players during one season. A total of eighty two NCAA Division III athletes (41 female [19.56 ± 1.34 yrs, 68.2 ± 10.84 kg, 166.3 ± 6.78 cm] and 40 male [19.97 ± 1.43 yrs, 75.45± 8.23 kg, 173.21 ± 7.65 cm]) volunteered to participate in this study which tested Q and H strength at 60°/s. A trend (p< 0.05) indicating that lower than 60% of HQR was associated with non-contact leg injuries was apparent. This suggests that the H:Q imbalance may be of significance in athletic non-contact leg injuries.

This study was designed to assess the reproducibility of head-neck musculo-tendinous stiffness (HMS) findings of the head-neck segment in response to quick-release in flexion and extension. The HMS was expressed as the slope of the isometric torque-angular displacement curve of the head-neck segment derived from the first 15 ms from the peak acceleration following release at different exertion levels (10% to 80% MVC). A test--retest methodology (7 days interval) was performed to assess the measurement reproducibility. The results showed a linear relationship between the flexion and extension torque and angular displacement (0.94 < R $^{2} $ < 0.99). Moreover, HMS findings evidenced good to excellent reproducibility using relative (ICC) as well as absolute (SEM) parameters. It was concluded that that simple kinematic assessment was appropriate for investigating HMS. Nevertheless, multiple-segmentation of the head-neck segment could lead, according to exertion level, to geometrical changes after the release.

Background: Fatigue is thought to impact performance and may be a factor in injury mechanism. However, the full impact of a potentially fatiguing task on performance is unclear.

Objective: To explore changes in maximum voluntary torque and electromyographic (EMG) activity following a sixty second isometric maximum voluntary contraction (MVC) of the quadriceps muscles and to follow the time course of any changes observed.

Method: 21 subjects (14 males and 7 females) were recruited. Torque during brief maximum voluntary isometric contractions of the quadriceps muscle group was recorded in right and left legs using a Cybex Norm Isokinetic Dynamometer before, during and at intervals after a 60 second isometric fatigue task. EMG activity of the vastus medialis, rectus femoris and vastus lateralis was also recorded synchronously.

Results: Mean peak torque was significantly (p< 0.05) lower in both legs at the end of the fatigue task. However, 10 minutes following the cessation of the task, it had increased and was significantly higher than the pre-fatigue level. It remained higher until the end of the protocol (30 mins post fatigue). The EMG amplitudes decreased slightly compared to pre-fatigue values during the fatigue task, a few of which were significantly lower than those of the pre-fatigue task. Following the fatigue task, EMG amplitudes increased gradually and were significantly higher than those of the pre-fatigue task in all the muscles at the final time point. Median frequencies decreased significantly during the fatigue task and were similar to pre-fatigue values by 5mins post-fatigue.

Conclusion: This study has revealed that both torque and EMG rise following a sustained isometric 60 second hold to higher levels than pre-hold and that this rise is maintained for up to 30 minutes. This rise however, was not associated with increased muscle firing frequency. The mechanisms behind this rise remain to be elucidated.

Background and objectives: Isokinetic test results are often evaluated against a norm or normal value. Previous research on isokinetics is prolific however, different populations present with different "normal" values. Thus, the aim of the present study was to establish isokinetic norms for the ankle, knee, shoulder, elbow and forearm joints in young, South African men.

Methods: Four hundred and thirty eight (N=438) young male participants (19.06 ± 1.86 yrs) were evaluated in terms of isokinetic peak torque of the ankle, knee, shoulder and forearm. A Cybex 340 isokinetic dynamometer was used to evaluate their concentric peak torque at a low velocity(30 or 60°/s); gravity was not corrected for. The data was tested for normality and the descriptive statistics were calculated. Percentile scores were subsequently constructed.

Results: Normative values for peak torque, peak torque per body mass and agonist-antagonist ratios were constructed for the ankle, knee, shoulder and forearm.

Conclusions: Results from this study might provide useful norms for the clinical evaluation of low-velocity, concentric peak torque in young males, when gravity correction is not performed.

The aim of this study was to investigate the correlations between knee extensor strength of the affected lower limb in patients with chronic stroke and other functional performance tests. Ten subjects with post-stroke hemiparesis (10 males; 54.3 ± 8.4 years old), who suffered from stroke for more than three years (duration of 8.7 ± 4.5 years) participated in this study. Knee extensor strength was measured using a hand-held dynamometer. Gait velocity was assessed when performing a 5-metre walk (5MWV), and additional parameters [the 5-minute walking distance(5MWD), the functional reach test (FRT), a timed up-and-go test (TUG) and Berg balance scale (BBS)] were also assessed as parameters of functional performance in each subject. It was demonstrated that knee extensor strength had significant Pearson's r correlation with 5MV (r=0.459, p< 0.05), FRT (r=0.781, p< 0.01), TUG (r=−0.538, p< 0.01) and BBS (r=0.758, p< 0.05). Therefore, knee extensor strength may be a moderate to good predictor of functional performance in patients with chronic stroke hemiparesis.

To determine the reproducibility of isokinetic and isometric hip flexion, extension, abduction and adduction strength scores in patients with hip osteoarthritis (N=16) and healthy subjects, testing was conducted twice 7 days apart. The patient group (PG) consisted of 16 subjects with unilateral or bilateral osteoarthritis of the hip (11 women, 5 men; age 56–75y). The control group (CG) included 13 age-matched healthy subjects (9 women, 4 men; age 54–73y). The standard error of measurement (SEM) served as the reproducibility outcome parameter.

The highest SEM values were obtained for hip extension measurements (15.4–16.7 Nm), followed by hip adduction (7.9–11.8 Nm) and hip flexion measurements (5.2–7.5 Nm). The smallest values were quantified for hip abduction measurements (4.7–7.7 Nm). PG showed larger values in all isometric measures except for hip extension and isokinetic hip abduction. When the 95% confidence interval is incorporated, these SEMs become significant.

Thus clinicians should be aware of the large measurement error in patients with hip OA. Adequate preparations and firm fixation of the pelvis are key elements to achieve reproducible results.

Hamstring injuries are common in many sports involving high-load eccentric hamstring activation, including Gaelic football. Eccentric hamstring peak torque (PT) and hamstring angle to peak torque (AngPT) have not been examined in previously injured Gaelic footballers. This study aimed to determine whether significant hamstring and quadriceps PT deficits were present in Gaelic footballers after a hamstring injury. Concentric hamstring and quadriceps PT at 60 and 180 degrees/second (°/s) and eccentric hamstring PT at 30°/s were measured using an isokinetic dynamometer in 18 male Gaelic footballers (nine previously injured, nine controls). Hamstring AngPT, as well as hamstring and quadriceps PT and PT ratios were analysed. For previously injured limbs, hamstring AngPT occurred at significantly shorter muscle lengths (p=0.038) than for the contralateral uninjured limbs in eccentric testing only. There were no other significant differences (p > 0.05) at any velocity, for within-subject or between-subject comparisons. The results showed that the previously injured hamstrings generated their eccentric hamstring AngPT at significantly shorter muscle lengths than the contralateral hamstrings. The results imply footballers with a previous hamstring injury who have returned to full participation may remain at increased risk of re-injury because of an alteration in their eccentric hamstring AngPT.

The aim of this study was to assess the reproducibility of isokinetic and isometric ankle dorsiflexor strength measurements in individuals with post-polio syndrome (PPS). Thirty-one men and women (mean age 63 ± 7.0 years) with verified PPS, participated in an intra-rater test-retest reproducibility study. Strength of the ankle dorsiflexor muscles in both lower limbs were measured twice, seven days apart, with a Biodex dynamometer(isokinetic concentric; 30°/s and isometric; ankle plantar flexion angle 10°). Reproducibility was evaluated with the intraclass correlation coefficient (ICC $_{2,1}$ ), the mean difference between the test sessions (�) and the 95% confidence intervals for �, the standard error of measurement (SEM, 95% SEM and SEM%) and Bland & Altman graphs. All 31 individuals completed the measurements in the less affected lower limb, but only 14 in the more affected lower limb due to severe weakness and/or joint stiffness. The analysis was therefore based on data from the two lower limbs separately. The test-retest agreements were high,(ICC $_{2,1}$ 0.85 to 0.94) and measurement errors generally small, and there was no discernible difference between the less and more affected lower limbs. The mean isokinetic and isometric peak torque (Nm) for the two lower limbs from the two test sessions ranged from 22.7 to 25.8. The SEM, which represents the limit for the smallest change that indicates a real change for a group of individuals, ranged from 2.51 to 3.74 Nm. In conclusion, isokinetic and isometric muscle strength measurements of the ankle dorsiflexor muscles in individuals with PPS are reproducible and can be used to detect changes over time or after an intervention for groups of individuals.