The effect of swimming on cartilage formation

Swimming is a non-weight-bearing exercise. Therefore it has the advantage of maintaining skeletal integrity in aged persons with weakened skeletal structures. Unlike other weight-bearing aerobic exercises, however, it does not appear to exert sufficient stimulus on bone-remodeling activities because the local load-bearing on bone tissues is mild. The purpose of this study was to investigate the effect of swimming on bone remodeling, especially with the use of implanted pellets containing bone morphogenetic protein (BMP) and demineralized bone matrix during the initial stages of the differentiation of mesenchymal cells to cartilage cells. Six-week-old female rats were divided into the swimming group and a control, nonswimming group. Test animals were forced to swim in a water bath for 30 min daily for 2 wk. After the swimming protocol, pellets were implanted and harvested. Messenger RNA isolated from pellets was quantified by means of a reverse transcription-polymerase chain reaction. The expression of RNAs for bone sialoprotein and BMP-6 in pellets from the swimming group was apparently enhanced at 7 d after implantation. These results suggested that systemic hormonal and/or metabolic changes that promote cartilage formation might have occurred after swimming because the effect was observed after the swimming protocol had ended and the pellets were implanted at a non-weight-bearing site.