Correction: Countermovement push-up test to assess the upper extremity force-time characteristics in swimmers during a macrocycle.

[This corrects the article DOI: 10.1371/journal.pone.0289573.].

Shoulder structures and strength in competitive preadolescent swimmers: A longitudinal ultrasonographic study.

BACKGROUND: Repetitive shoulder movements during competitive training may cause changes in the strength of periarticular shoulder structures in preadolescent swimmers. OBJECTIVE: To prospectively determine the effects of training on shoulder periarticular structures and muscle strength in preadolescent swimmers. DESIGN: Prospective cohort study. SETTING: Community-based natatorium. PARTICIPANTS: Twenty-four preadolescent swimmers aged 10-12 years. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Measurements were repeated in three periods as preseason, midseason, and postseason. Ultrasonographic measurements (supraspinatus tendon thickness, humeral head cartilage thickness, deltoid muscle thickness, and acromiohumeral distance) were performed using a portable device and a linear probe. Shoulder (flexion, extension, abduction, internal and external rotation) and back (serratus anterior, lower, and middle trapezius) isometric muscle strength were measured with a handheld dynamometer. RESULTS: Supraspinatus tendon thickness and acromiohumeral distance were similar in all periods (all p > .05); however, deltoid muscle and humeral head cartilage thicknesses increased throughout the season (p = .002, p = .008, respectively). Likewise, whereas shoulder muscle strength increased (all p < .05), back muscle strength was similar in all periods (all p > .05). CONCLUSIONS: In preadolescent swimmers, acromiohumeral distance and supraspinatus tendon thickness seem to not change; but humeral head cartilage and deltoid muscle thicknesses as well as shoulder muscle strength increase throughout the season.

Countermovement push-up test to assess the upper extremity force-time characteristics in swimmers during a macrocycle.

Although it is known that swimming training can improve upper extremity performance, the force-time characteristics of the upper extremity during different training periods are not well understood. The objective of this study was to measure changes in the force-time characteristics of the upper extremity of young swimmers during different training periods within a season. Seventeen young swimmers, comprising 5 males (age: 15.4 ± 0.54 years); 12 females (16.4 ± 2.6 years) participated in this study. They were tested at four experimental test time points: baseline (E1), post-general preparation (E2), post-specific preparation (E3), and taper season (E4). The countermovement push-up test was performed using a force plate to measure force time parameters. Differences in force, time, velocity and impulse parameters were evaluated between the different periods. The study found that vertical take off velocity significantly increased across the assessed periods (F = 11.79; p = .001; η2 = .424), with significant increases from E1 to E2 (p < .001) and from E3 to E4 (p = .016). Flight Time also significantly increased across the assessed periods (F = 11.79; p = .001; η2 = .424), with significant increases from E1 to E2 (p < .001), from E1 to E4(p = .001), and from E3 to E4 (p = .005). The Force Impulse significantly increased throughout the assessed periods (F = 5.84; p = .012; η2 = .267), with significant increases from E1 to E2, (p = .006), from E1 to E3 (p = .016), and from E1 to E4 (p = .003). As this study shows, periods of increased training intensity can affect athletic progression, even though training aims to improve strength, speed, and performance. While some practical aspects such as strength, flight time, and impulse parameters may change during a macrocycle, the countermovement push-up test can provide trainers with an alternative and convenient way to monitor anaerobic force, speed, and performance, as well as measure explosive force-time performance in the upper body.

The effect of swimming and type of stroke on bone metabolism in competitive adolescent swimmers: a pilot study.

BACKGROUND/AIM: Physical activity plays a key role in increasing and preserving bone mineral density (BMD). Effects on bone development associated with various nonweight-bearing sporting activities, such as swimming, are controversial. Different strokes used in swimming may also present as another factor. The aim of this study was to evaluate the effect of swimming and type of stroke on BMD in competitive adolescent athletes. MATERIALS AND METHODS: Seventy-nine swimmers between the ages of 10 and 21 years participated in this study. BMD was measured with dual-energy X-ray absorptiometry at the lumbar vertebrae and left proximal femur. Daily calorie intake and calcium consumption, and measurements of calcium, phosphorus, alkaline phosphates, 25-hydroxyvitamin D (25(OH) D), and osteocalcin were evaluated. RESULTS: Preliminary results revealed that the type of stroke had no effect on BMD (P = 0.79). Additionally competitive swimmers did not have augmented bone mineral accretion, and in 13.9% of athletes low BMD was confirmed. Sixty percent of swimmers had either deficient or insufficient 25(OH) D levels and a low mean calorie (P = 0.542) and calcium (P = 0.038) intake was observed. CONCLUSION: This was the first study to evaluate the effect of swimming stroke on BMD. Although no effect was statistically shown, further studies with a larger series may determine this effect.

Physical activity intensities during school time in healthy prepubertal boys and BMI.

The first aim of this study was to determine the intensity of physical activity (PA) by an objective measurement method - using an accelerometer in Turkish prepubertal boys. The second aim of this study was to correlate the intensity of PA with body mass index (BMI). For this aim 40 boys were participated in this study. PA levels were measured by using GT3X-bt accelerometer for 5 consecutive school days. Mean BMI was found 17.56 ± 2.39. 101.20 ± 17.82 minutes was found as moderate to vigorous physical activity (MVPA) per school day. Significant negative moderate correlation was found among vigorous PA, weight and BMI (r= -.39; -.38). The main finding of this study is: there is a relationship between vigorous PA and BMI in prepubertal boys. This means that the most effective intensity of MVPA in preventing the increase of BMI in prepubertal boys is the vigorous PA.