The Johnson antishear device and standard shin pad in the isokinetic assessment of the knee

Quadriceps activation during maximal isometric and isokinetic contractions: The minimal real difference and its implications

BACKGROUND: A method of measurement of voluntary activation (VA, percent of full muscle recruitment) during isometric and isokinetic concentric contractions of the quadriceps femoris (QF) at 60∘/s and 120∘/s was previously validated. OBJECTIVE: This study aimed to quantify the test-retest minimal real difference (MRD) of VA during isometric (ISOM) and isokinetic concentric contractions of QF (100∘/s, ISOK) in a sample of healthy individuals. METHODS: VA was measured through the interpolated twitch technique. Pairs of electrical stimuli were delivered to the QF at 40∘ of knee flexion during maximal voluntary contractions. Twenty-five healthy participants (20–38 years, 12 women, 13 men) completed two testing sessions with a 14-day interval. VA values were linearized through logit transformation (VAl). The MRD was estimated from intraclass correlation coefficients (model 2.1). RESULTS: The VA (median, range) was 84.20% (38.2–99.9%) in ISOM and 94.22% (33.8–100%) in ISOK. MRD was 0.78 and 1.12 logit for ISOM and ISOK, respectively. As an example, in terms of percent VA these values correspond to a change from 76% to 95% and from 79% to 98% in ISOM and in ISOK, respectively. CONCLUSIONS: The provided MRD values allow to detect significant individual changes in VA, as expected after training and rehabilitation programs.

Effect of subject restraint and resistance pad placement on isokinetic knee flexor and extensor strength: implications for testing and rehabilitation

BACKGROUND

In clinical practice, several subject restraint and resistance pad placement variations are used when an isokinetic knee flexion/extension test is performed. However, it is unknown if these variations affect the outcome measures. The aims of this study were to determine if these setup variations affect isokinetic outcomes and to establish the smallest detectable difference for these setup variations.

HYPOTHESIS

Variation in isokinetic setup affects outcome measures.

STUDY DESIGN

Cross-sectional repeated-measures crossover study.

METHODS

Ten recreationally active adult men were examined with isokinetic dynamometry on 4 separate days. In the first 3 days, fully strapped and trunk-unstrapped testing was conducted with the resistance pad placed distally on the shin. On days 1 and 3, the unstrapped condition was performed first, followed by the strapped condition. On day 4, the resistance pad was placed proximal on the shin (anterior cruciate ligament testing).

RESULTS

There were no within-condition differences for days 1, 2, or 3 for the strapped and unstrapped conditions (P > 0.05). Between-condition comparisons were significant (eg, quadriceps peak torque, P < 0.001; hamstring peak torque, P = 0.043) for the strapped, unstrapped, and proximal resistance pad placement conditions. The strapped condition generally showed the largest torques, and the unstrapped, the least. The smallest detectable differences were relatively large (eg, quadriceps peak torque strapped = 20.6%). The greatest intraclass correlation values were found when strapped.

CONCLUSIONS

Subject setup significantly influences isokinetic outcome measures at the knee. Since the strapped condition demonstrated the greatest repeatability, it is recommended. The smallest detectable differences were relatively high for all variables and should be considered in the interpretation of the effect size of interventions.

CLINICAL RELEVANCE

Subject setup strapping must be considered when investigating test-retest values or when comparing subjects after isokinetic testing at the knee. The fully strapped condition has the best repeatability and highest torque values.

Quadriceps Activation during Knee Extension Exercises in Patients with ACL Pathologies

This study assessed muscle inhibition in patients with chronic anterior cruciate ligament (ACL) deficiency or ACL reconstruction. A series of protocols were tested for their effectiveness in increasing activity of the individual knee extensor muscles and decreasing muscle inhibition of the whole quadriceps group. Quadriceps muscle inhibition was measured by superimposing an electrical twitch onto the quadriceps muscle during a maximal voluntary knee extension. The level of activation of the individual knee extensor and knee flexor muscles was assessed via electromyography (EMG). Patients with ACL pathologies showed strength deficits and muscle inhibition in the knee extensors of the involved leg and the contralateral leg. Muscle inhibition was statistically significantly greater in ACL-deficient patients compared to ACL-reconstructed patients. When a knee extension was performed in combination with a hip extension, there was a significant increase,p< 0.05, in activation of the vastus medialis and vastus lateralis muscles compared to isolated knee extension. The use of an anti-shear device, designed to help stabilize the ACL-deficient knee, resulted in increased inhibition in the quadriceps muscle. Furthermore, a relatively more complete activation of the vasti compared to the rectus femoris was achieved during a fatiguing isometric contraction. Based on the results of this study, it is concluded that performing knee extension in combination with hip extension, or performing fatiguing knee extensor contractions, may be more effective in fully activating the vasti muscles than an isolated knee extensor contraction. Training interventions are needed to establish whether these exercise protocols are more effective than traditional rehabilitation approaches in decreasing muscle inhibition and achieving better functional recovery, including equal muscle strength in the injured and the contralateral leg.

A quantifiable approach in the comparison of isokinetic assessment data--new correlation equations for the Johnson antishear device and standard shin pad in the isokinetic assessment of the knee

The rehabilitation of the knee with a deficient anterior cruciate ligament (ACL) always presents a great challenge. Isokinetic assessment allows muscle performance to be quantified. The antishear device, introduced by Johnson, has the distinct advantage of minimizing the anterior translation force during isokinetic exercise. In a previous report, there was a significant difference between the Johnson double pad antishear device and the standard single pad device in knee extension. The main purpose of this study was to define a correlation equation such that data generated in the use of the two different devices can be compared for assessment. Ten subjects were tested with the Cybex isokinetic dynamometer with a randomly selected sequence of test speeds. Correlation coefficient (r), regression analysis and paired t tests (P) were performed to estimate the correlation and difference between the two devices. It is concluded that a significant difference in the data generated between the two devices indicated that a single device should be selected to carry out a series of comparisons on a particular subject. However, if the two devices are used in a series of testings, a set of correlation equations has been defined to facilitate such comparison. The findings in this study will widen the application of comparison of isokinetic data in the quantitative approach of rehabilitation of the knee with a deficient anterior cruciate ligament.