Simplified Measurement of Maximum Strength After Knee Surgery: Application-Based Knee-Training Device Compared to Isokinetic Testing

Abstract

Context: Isokinetic testing is used as a standard tool in measuring strength in professional athletes. It is often used to evaluate improvement during rehabilitation. The disadvantages of isokinetic testing include its costs, the fact that it is not portable, and its risk of injury, which makes it not suitable for early postoperative rehabilitation.

Hypothesis: The aim of this study was to investigate the relationship between the results of the isokinetic testing and the measurements of an application-based knee-training device.

Study design: Exploratory diagnostic study.

Methods: In this monocentric study, 100 subjects performed an isokinetic maximum strength examination and an assessment on the application-based knee-training device in a randomized order. The isokinetic testing was based on the Swiss Olympic protocol with 3 sets of 5 repetitions of maximum strength testing for flexion and extension. The subjects consisted of 50 healthy professional athletes and 50 healthy recreational athletes, half male and half female, between the ages of 18 to 30 years old.

Results: No medical or technical issues were reported. The analysis of the relationship between application-based knee-training device and extension showed a Pearson correlation coefficient of r=0.667 for the left knee and r=0.604 for the right knee. For flexion, the Pearson correlation coefficient was r=0.640 for the left side and r=0.673 for the right side. When strength measured by the application-based knee-training device was adjusted for height and weight of the subjects, the Pearson correlation was even stronger (extension left: r=0.727, right: r=0.689; flexion left: r=0.641, right: r=0.711).

Conclusion: The study shows a moderate to high correlation between isokinetic testing and the application-based knee-training device. These results suggest that the application-based knee-training device is effective for early strength rehabilitation without the risk of injury.

Keywords: app-based rehabilitation; exergame; isokinetic; knee.

Figure 1

Linear relationship of isokinetic results for extension and knee-training device results separately for right and left knee. Pearson correlation for the left and right knee is 0.667 and 0.604.

Figure 2

Linear relationship of isokinetic results for flexion and knee-training device results separately for right and left knee. Pearson correlation for the left and right knee is 0.640 and 0.673.

Figure 3

Linear relationship of isokinetic results for extension and predicted results based on KT results, weight and height separately for right and left knee. Pearson correlation coefficients for the left and right knee are 0.727 and 0.689.

Figure 4

Linear relationship of isokinetic results for flexion and predicted results based on KT results, weight, and height separately for right and left knee. Pearson correlation coefficients for the left and right knee are 0.641 and 0.711.

Figure 5

Modified Bland–Altman plot of the difference of the predicted isokinetic extension value from the true isokinetic extension value. Mean differences and 95% limits of agreement calculated by mean difference ±1.96 standard deviation are given separately for left (−193.3; 202.73) and right knee (−217.19; 207.75). Mean difference is 4.72 (±101.03) for the left knee and −4.72 (±108.40) for the right knee.

Figure 6

Modified Bland–Altman plot of the deviation of the predicted isokinetic flexion value from the true isokinetic flexion value modified. Mean differences and 95% limits of agreement calculated by mean difference ±1.96 standard deviation are given separately for left (−143.40; 159.93) and right knee (−152.83; 136.31). Mean difference is 8.26 (±77.38) for the left knee and −8.26 (±73.76) for the right knee.