Variability in antagonist muscle activity and peak torque during isometric knee strength testing

Abstract

Background & objective: Strength testing is common in the treatment of people with knee pathology and in research related to knee health. Variability in the magnitude of antagonist muscle activity and peak torque measurements during isometric knee strength testing is not well defined and has potential implications of strength test validity and reliability. The aim of this study was to determine the magnitude and variability (side-to-side, session-to-session) of antagonist muscle activity and peak torque during isometric knee strength testing and to compare and contrast the results of males and females.

Methods: Electromyograms and torque data were collected from 30 active young people (15 males, 15 females) during isometric strength testing of the knee extensors and flexors at two sessions that took place approximately one week apart. The magnitude of antagonist muscle activity and peak torque during isometric knee strength testing was calculated and the variability in these parameters assessed.

Results: Significant side-to-side differences were observed in the magnitude of antagonist muscle activity when the leg with higher antagonist activity was contrasted with the leg with lower antagonist activity (P < 0.001). Significant side-to-side differences were also observed when peak torque measurements were contrasted in a similar manner (P < 0.001). No significant differences were observed in peak torque and antagonist activity measurements between sessions. Significantly higher vastus medialis antagonist activity was observed in females (P < 0.001).

Conclusions: Our findings suggest that significant variability in antagonist muscle activity and peak torque is present during maximal isometric knee strength testing. This variability may reduce the accuracy of knee strength tests, especially when side-to-side comparisons are made as is typical in clinical settings. The results of this study may be helpful when interpreting strength test results and setting criteria for patient progression.

Figures

Figure 1

A subject performing an isometric knee strength test on the test system.

Figure 2

A sample raw electromyographic recording of muscle activity with associated torque traces from a subject's isometric knee extensor and flexor strength tests. The agonist (black) and antagonist (red) activity of the five knee muscles tested demonstrate the noteworthy antagonist activity during isometric knee strength testing. Arrows indicate the epoch at which the subject produced peak torque values. VL: Vastus Lateralis; RF: Rectus Femoris, VM: Vastus Medialis; MH: Semitendinosus; LH: Biceps Femoris Longus.

Figure 3

Plots demonstrating the difference between the mean normalized antagonist activity by side for the 5 muscles of the male and female subjects when the values of the leg that produced higher antagonist activity was contrasted with those from the leg that produced lower antagonist activity. Bold colored lines represent the mean for all subjects irrespective of the sex of the subject. All muscles exhibited significant differences between sides (P<0.001). Females had significantly higher VM antagonist activity when compared to males (P= 0.001). Note the limb that produced lower VM antagonist activity in females is similar in magnitude to the limb that produced higher VM in males. VL: Vastus Lateralis; RF: Rectus Femoris, VM: Vastus Medialis; MH: Semitendinosus; LH: Biceps Femoris Longus.

Figure 4

The mean normalized antagonist activity for the 5 knee muscles contrasted between left and right side (A) and across test sessions (B). Note that there are no differences in the magnitude of antagonist activity between left and right side and across test sessions. Error bars represent standard error of the mean. VL: Vastus Lateralis; RF: Rectus Femoris, VM: Vastus Medialis; MH: Semitendinosus; LH: Biceps Femoris Longus.

Figure 5

The mean peak torque for the knee extensors and flexors when contrasted as left versus right side was not significantly different. Conversely, significant differences (P