Quantifying the Effects of Different Treadmill Training Speeds and Durations on the Health of Rat Knee Joints

Abstract

Background: Walking and running provide cyclical loading to the knee which is thought essential for joint health within a physiological window. However, exercising outside the physiological window, e.g. excessive cyclical loading, may produce loading conditions that could be detrimental to joint health and lead to injury and, ultimately, osteoarthritis. The purpose of this study was to assess the effects of a stepwise increase in speed and duration of treadmill training on knee joint integrity and to identify the potential threshold for joint damage.

Methods: Twenty-four Sprague-Dawley rats were randomized into four groups: no exercise, moderate duration, high duration, and extra high duration treadmill exercise. The treadmill training consisted of a 12-week progressive program. Following the intervention period, histologic serial sections of the left knee were graded using a modified Mankin Histology Scoring System. Mechanical testing of the tibial plateau cartilage and RT-qPCR analysis of mRNA from the fat pad, patellar tendon, and synovium were performed for the right knee. Kruskal-Wallis testing was used to assess differences between groups for all variables.

Results: There were no differences in cartilage integrity or mechanical properties between groups and no differences in mRNA from the fat pad and patellar tendon. However, COX-2 mRNA levels in the synovium were lower for all animals in the exercise intervention groups compared to those in the no exercise group.

Conclusions: Therefore, these exercise protocols did not exceed the joint physiological window and can likely be used safely in aerobic exercise intervention studies without affecting knee joint health.

Keywords: Aerobic exercise; Animal model; Cyclical loading; Histology; Joint health; Osteoarthritis.

Fig. 1

a Travel distance per week per group. Notice, the control group was exposed to a constant amount of exercise throughout the protocol, 150 m per week. For the other groups, there was a gradual increase in the amount of exercise from week 2 to week 5. From week 5 to the end of the intervention period, the levels of exercise were constant for rats in the MD and HD groups. For rats on the EHD group, the exercise distance doubled, tripled, and quadrupled in weeks 10, 11, and 12 compared to weeks 5–9, respectively. b Body fat. % body fat measured in the end of the experimental protocol. c Total modified Mankin scores: No significant differences were found between groups. MD moderate duration exercise, HD high duration exercise, EHD extra high duration exercise. * indicates significant difference when compared to control group. # indicates significant difference when compared to moderate duration group

Fig. 2

a Cartilage thicknesses across six sites on the knee joint measured through histology. No significant differences were found between groups. b COX-2 mRNA levels for the synovium expressed as fold change from control group (dashed gray line). c EGF exhibiting significant differences between groups for synovial fluid; 27 proteins were analyzed with a Luminex-based protein assay. MD moderate duration exercise, HD high duration exercise, EHD extra high duration exercise, MFC-ant anterior medial femoral condyle, MFC-post posterior medial femoral condyle, LFC-ant anterior lateral femoral condyle, LFC-post posterior lateral femoral condyle. * indicates a significant difference when compared to control group values