Effect of Plyometric Exercises in Premenopausal Women

Depending on various factors, bone mass begins to decrease with aging and this may lead to the osteoporosis. Physical activity and regular exercise provides an increase in bone mineral density (BMD). It is mentioned that there are relationships between muscle strength and BMD and also muscle strength has positive effects on BMD. In the literature it is showed that postmenopausal women with weaker trunk muscle strength could have risk of osteoporosis.

Plyometric exercises are used to increase muscle strength. Physiological basis of plyometric exercise consist of stretch-shortening cycle and thus it is effective in increasing the force. At the same time, plyometric exercises have positive effects on BMD because of weight bearing exercises.

The aim of this study was to investigate the effects of plyometric exercises on hip and trunk muscle strength in premenopausal women.

Participants and Study Design: Twenty six sedentary premenopausal women aged 35-50 years participated this study. Participants were assigned into three groups: Plyometric Exercise Group (PG; n=10), Isokinetic Exercise Group (IG; n=8), Control Group (CG; n=8). Participants were informed about the procedures of the study and signed a written voluntary consent form in accordance with the Declaration of Helsinki. The study protocol was approved by the Ethical Committee of the Istanbul University Medical Faculty. Measurements and training sessions were performed in the Istanbul University Medical Faculty Sport Medicine Department's Laboratory.

Measurements: Muscle strength was determined by using a Cybex Norm isokinetic dynamometer (Cybex Humac Norm, USA). Range of motion was set from 10 degree extension to 40 degree flexion. Isokinetic concentric contraction strength was measured at angular velocity of 60 degree per second and 90 degree per second. Subjects performed 3 trials trunk flexion and extension contractions at minimal exertion and 4 test repetitions at maximal trunk flexion and extension.

The hip abduction adduction isokinetic testing was performed in side lying position. Hip muscle strength was measured at angular velocity of 30 degree per second. Range of motion was set from 10 degree adduction to 40 degree abduction. Subjects performed 4 trials at minimal exertion and 4 test repetitions. Dominant leg values were analyzed for hip. All subjects performed warm-up and stretching exercises before testing.

Beck Depression Inventory (BDI) and State-Trait Anxiety Inventory (STAI) were used to asses depression and anxiety conditions.

Interventions: The training sessions were performed three days a week for six weeks. All exercise sessions were supervised by a physiotherapist.

Each session was consisted of warm-up, plyometric exercises and cool-down periods in PG. The warm-up and cool-down periods were performed by walking on the treadmill and lower extremity stretching exercises. The plyometric exercise training period involved vertical jumping, forward and back jumping and lateral jumping. After fifth session the number of repetitions were increased depending of toleration of participants. After tenth session step bench jumping exercise and after fifteenth session diagonal jumping exercise were added and study was completed in eighteen session.

In IG, isokinetic exercises were performed by using a Cybex Norm isokinetic dynamometer with an incorporated trunk flexion/extension unit in a standing position. Range of motion was set from 10 degree extension to 40 degree flexion. Each session was consisted warm-up, isokinetic exercises and cool-down periods. Warm-up and cool-down periods were consisted trunk exercise and stretching. Isokinetic exercises were performed 7 repetitions at angular velocity of 90 degree per second , 6 repetitions at angular velocity of 75 degree per second and 5 repetitions at angular velocity of 60 degree per second.

Participants in CG were assessed baseline and at sixth week.