Concentric trunk extensor (abdominal)/concentric trunk flexor (lower back) and concentric lower limb extensor (quadriceps)/concentric lower limb flexor (hamstrings) strength was measured using a Biodex System 3 isokinetic dynamometer (Biodex Medical Systems, Shirley, NY, USA). Peak torque/body weight ratios were statistically analyzed as the measure of muscle strength (24). To minimize the risk of injury of the subjects, a 10-minute warm-up and cool-down protocol was followed before and after pre and postmeasurements. The protocol consisted of walking on a treadmill at a speed set at 40% of their age predicted maximal heart rate for 5 minutes because this is the minimum intensity required in the literature (1). The conventional age predicted heart rate formula (HRmax = 220 − age) was used to calculate the maximal heart rate. The walking was followed by light static stretches involving the major muscle tendon groups of the body for 2 sets of 15 seconds (46).
Isokinetic Measurement of Trunk Extensor (Abdominals)/Flexor (Lower Back) Strength
The isokinetic measurement of concentric trunk extensor (abdominal)/concentric trunk flexor (lower back) torque was taken using the isokinetic dynamometer at speeds of 60 and 90° s−1 (27). The subjects were seated in the dynamometer with their back and neck in a neutral position. The feet were placed on an adjustable pad. The thighs, pelvis, and chest were constrained by rigid pads to facilitate isolation of the trunk for flexion/extension testing only (44). Before the actual measurements, subjects performed a 5-repetition warm-up test. After a 10-second rest period, they performed 10 repetitions at each angular velocity.
Isokinetic Measurement of Extensor (Quadriceps)/Flexor (HamStrings) Strength
Isokinetic measurement of concentric lower limb extensor (quadriceps)/concentric lower limb flexor (hamstrings) torque was measured using the isokinetic dynamometer at speeds of 60 and 90° s−1, and 60 and 240° s−1, respectively. The isokinetic quadriceps/hamstrings strength measurements were made on separate days followed by the posterior trunk isokinetic measurements to avoid any negative effects on the results. The subjects were positioned in the dynamometer with their hip joint at approximately 90° flexion, their upper bodies secured with dual cross over straps, and their waist secured by a waist strap. The range of motion of the knee was set at 90° of full extension, with the upper leg secured using the thigh strap to limit excess movement of the knee and limb. Full knee extension was standardized between the testing sessions by equalizing knee joint angles with a handheld goniometer for accuracy of the results. Angular velocity was set at 60° s−1 with 5 repetitions performed for each leg (14). Both legs of the participants were measured individually after the identification of dominant and nondominant legs. The dominant and nondominant legs were determined by the examiner by asking which leg the subjects would use to kick a soccer ball.
Trunk Extensor (Lower Back) Endurance
The trunk extensor (lower back) muscular endurance was assessed by the number of back extensions completed without rest using modified Sorensen test (35). The trunk of the subjects was positioned horizontally unsupported from the upper border of the iliac crest while prone on an examination table. During the test, the buttocks and legs were fixed to the table by 3 wide straps, and the hands were placed at the side of head (38). The subjects were instructed to perform back extensions within a range of 45° while maintaining the natural lordic curve. The examiner gave instructional and verbal cues during the test. The number of repetitions was recorded when subjects could no longer remain horizontal.
Trunk Flexor (Abdominal) Endurance
Trunk flexor (abdominal) muscular endurance was assessed by the curl-up test (21). The arms were placed at the sides, palms facing down with the middle fingers touching a piece of masking tape. A second piece of masking tape was placed 12 cm apart. Feet were flat on the ground with knees bent at 90°. Shoes were worn during the test. A metronome was set to 50 b·min−1, and the subjects did slow, controlled curl-ups to lift the shoulder blades off the mat in time with the metronome. The subjects performed as many curl-ups as possible without pausing by touching their finger tips to both pieces of the masking tape.
Trunk Extensor (Lower Back) Flexibility
Trunk extensor (lower back) flexibility was measured by the sit and reach test (22). A box was vertically marked in centimeters on top and had a movable yardstick at the 0-cm edge. The subjects removed their shoes before the test. The subjects sat on the floor keeping their legs straight with the soles of their feet touching the box. They put their finger tips on the 0-cm edge of the box and pushed the yardstick as far as they could while maintaining the position of their legs. The best score of 3 trials was recorded in centimeters.
Lower Limb Endurance
Lower limb endurance was measured by repetitive squat test (30). The subjects stood with feet shoulder width apart. They were instructed to squat until their thighs were horizontal to the ground and then return to the upright position with knees slightly bent. A metronome was set to 60 b·min−1 to maintain the repetition pace of the squat. The upward (concentric) portion of the squat was 1 second, and the downward (eccentric) portion of the squat was 1 second. The number of repetitions that the subjects could perform in the proper form was recorded.
Functional reach test was used to measure dynamic balance (17). The subjects stood next to a wall with a comfortable stance width. They were then required to make a fist with their preferred arm and to reach as far as possible while keeping the arm parallel to the ground. The distance that subjects could reach forward holding their arm parallel to the ground was measured in centimeters. The subjects performed 1 practice trial and 2 tests. The mean score of the test measurements was recorded.
All statistical analyses were conducted using SPSS version 11.5 (SPSS, Inc, Chicago, IL, USA). A 2-way within-subject analysis of variance was conducted to investigate pre and posttest scores for the lower limb extensor (quadriceps) and lower limb flexors (hamstrings) isokinetic strength measurements. Paired sample t-tests were conducted to compare pre and posttest scores of trunk extensor (back) and trunk flexor (abdominal) isokinetic strength, dynamic balance, trunk extensor (lower back) muscular endurance, trunk flexor (abdominal) muscular endurance, flexibility, and lower limb muscular endurance. Statistical power was computed and reported as observed power. The level of significance was set at p ≤ 0.05.
Trunk Flexor (Abdominals) and Extensor (Lower Back) Strength
The pre and postmeasurements of the isokinetic testing of trunk flexor (abdominals) and extensor (lower back) muscles at 60 and 90° s−1 are presented in Table 2.
Statistical analysis showed a significant difference (p = 0.00, observed power = 0.99) between pre and post isokinetic tests for trunk flexor (abdominal) at 60°. Statistical analysis of pre and post isokinetic tests for trunk flexor (abdominal) strength was also significant (p = 0.00, observed power = 0.99) at 90°.
According to the statistical analysis, isokinetic pre and posttest values for trunk extensor (lower back) results were significant (p = 0.001, observed power = 0.97) at 60°. Statistical analysis of pre and postisokinetic tests for trunk extensor (lower back) was also significant (p = 0.00, observed power = 0.99) at 90°.
Lower Limb Extensor (Quadriceps)/Flexor (Hamstrings) Strength
The pre and postisokinetic testing of lower limb extensors (quadriceps) and flexors (hamstrings) at 60 and 240° s−1 showed significant improvement (p ≤ 0.05) (Table 3). The pre and postmeasurements of the lower limb extensor (quadriceps) dominant leg and nondominant leg showed a significant improvement (p = 0.003, observed power = 0.89) at 60°. There was also a significant difference (p = 0.000, observed power = 0.98) between the pre and postmeasurements of the dominant leg and nondominant leg at 240°.
The pre and postmeasurements of the lower limb flexors (hamstrings) dominant leg and nondominant leg were significant (p = 0.000, observed power = 1.00) at 60°. The pre and postmeasurements of the dominant leg and nondominant leg were also significant (p = 0.005, observed power = 0.86) at 240°.
Trunk and Lower Limb Endurance, Lower Back Flexibility, and Balance
According to the results of paired sample t-test for the pre and posttests of trunk flexor (abdominal) endurance (p = 0.00, observed power = 0.99), trunk extensor (lower back) endurance (p = 0.00, observed power = 0.99), lower limb endurance (p = 0.00, observed power = 0.99), trunk extensor (lower back) flexibility(p = 0.00, observed power = 0.99), and dynamic balance (p = 0.001, observed power = 0.93) revealed a significant difference (p ≤ 0.05) (Table 4).
This paper tries to shed light on the effects of a Swiss-ball core strength training protocol on trunk extensor (lower back) and flexor (abdominal) and lower limb extensor (quadriceps) and flexor (hamstring) muscular strength, abdominal and lower back and lower limb endurance, lower back flexibility, and dynamic balance in sedentary women. The results supported our hypothesis that Swiss-ball core strength training exercises can improve strength, endurance, flexibility, and balance in sedentary women.
The Swiss-ball core strength training protocol used in this study aimed at providing the coactivation of global and local muscles of the core. The results of the 8-week Swiss-ball core strength training exercise protocol showed significant improvements in both the endurance and strength of the lower back and abdominals. Based on the studies in the literature that suggest that exercises such as curl-ups, double leg lowering, and push-ups performed on a Swiss-ball increase the level of muscular activity of the abdominals and obliques more than curl-ups, double leg lowering, and push-ups performed on a stable surface (6,9,32,39,48), these findings seem congruent. Despite the fact that the surface electromyographic measurements used in these studies merely assessed the activity of the superficial global muscle groups, the authors suggested that the motor control system required the coactivation of the global and local muscles to stabilize the spine to maintain balance and prevent the threat of falling off the Swiss ball.
As Anderson and Behm (2) suggest, the proprioceptive system relies on information from the joints and muscles to coordinate unconscious reflexes to maintain balance. According to Lehman et al. (29) local muscles have a greater proprioceptive function, and if the Swiss-ball stresses these muscles to a greater extent, this may form the basis for an improved balance effect after training. In this line, the significant improvement in dynamic balance in our study provides very important evidence that the Swiss-ball core strength training protocol in this study can not only facilitate the global muscles but can also facilitate the local muscle groups of the core. Therefore, this Swiss-ball core strength training protocol can be implemented as a preventative training against falls and subsequent injuries in the sedentary women that is related to poor balance, lower limb and core strength (8,49).
Low back pain has been described as a disease associated with sedentary lifestyle. In this particular context, it has been emphasized that low back pain can be a result of weak lower limb, abdominal and back muscles, and poor flexibility of lower back and hamstring muscle groups (16,18,28). A study conducted by Lee et al. (28) showed that subjects with a history of low back pain had weaker trunk muscle strength when compared to those who had not experienced low back pain. Similarly, a study of the youth in Finland found that low level of physical activity and decreased spinal and abdominal muscle strength characterized those who developed low back pain (42). Athletes who experience lower back pain while running and playing tennis and golf were also characterized by lack of core muscular strength (20,23,37,43,47). Therefore, Swiss-Ball exercises were emphasized as an effective training tool to increase core strength, improve spinal stability and flexibility in physiotherapeutic treatments and athletics (4,9,20,37). From this stand point, the significant results in this study denote that the Swiss-ball exercise protocol used in this study can be recommended as a preventative training method against low back pain in sedentary women (12).
On 1 level, we suggest that the Swiss-ball exercise protocol used in this study proved effective in improving flexibility of the lower back muscles, but on another level, one may consider that the static stretches included in the warm-up and cool-down phases of the Swiss-ball exercise intervention may have contributed to this result. However, the latest research showed that static stretching before and after exercise does not improve flexibility (5). Thus, the improvements in flexibility can be related to the dynamic exercises performed on the Swiss ball that provide increased range of movements (15,19). In conclusion, this study showed that sedentary women can benefit from the Swiss-ball core strength training protocol used in this study by means of improved core muscular strength, endurance, flexibility, and balance as an enjoyable and cost-effective training for the prevention of low back pain, falls, and recovery from lower back injuries in sedentary adults that can help increase their quality of life in return (48).
This study provides practical implications for physiotherapists, strength and conditioning specialists who supply exercise programs for sedentary people. The Swiss-ball core strength training protocol used in this study can be done in isolation or integrated into training programs to strengthen the core musculature. The exercises can be gradually modified to complement for individual differences and needs. For instance, gym balls can be held while doing Swiss-ball straight arm crunches to provide more resistance according to the individual's level of physical condition. Yet, the increased risk of falling and subsequent injury because of the unstable characteristic of the Swiss balls should not be ignored (29). Therefore, all safety precautions must be checked and taken before exercising. It is also advised to follow a progressive training system for the adaptation of the stabilizing core musculature (11,26).
We would initially like to thank Prof. Feza Korkusuz, chair of Physical Education and Sports Department at Middle East Technical University, Ankara, Turkey, for providing funds for this study. We would also like to express our gratitude to our colleague Mutlu Cug for his patience, effort, and collaborative work during this project. Finally, special thanks go to the Physical Education and Sports Department, Directorate of Sports and Health and Caring Centre at Middle East Technical University, Ankara, Turkey, for supporting and letting us use their facilities and laboratories all through our research. The corresponding author Betül Sekendiz is currently enrolled in a Ph.D. program in Sport Management at Health Sciences and Medicine Faculty at Bond University, Gold Coast, Australia.
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Keywords:© 2010 National Strength and Conditioning Association
stability ball; low back pain; spinal stability; falls