Force production during maximal front crawl tethered swimming: exploring bilateral asymmetries and differences between breathing and non-breathing conditions

The present study focused on propulsive forces applied during tethered swimming. The main aims were to identify asymmetries between dominant and non-dominant arms, quantify the effect of breathing on force application and, explore any association between each variable and swimming performance. Fifteen regional level swimmers completed a maximal front crawl tethered swimming test, with maximal kicking, under four conditions: 1) Dominant arm strokes only, no breathing; 2) non-dominant arm strokes only, no breathing; 3) full stroke, no breathing; 4) full stroke, breathing on the preferred side. The outcome variables were: absolute and normalised (force divided by body mass) minimum, mean and maximum force; stroke cycle time and; impulse. The symmetry index was also calculated, and all variables were correlated with the swimmers' season best times in 50 m front crawl. Some bilateral force asymmetries were found, but they did not always favour the dominant side and were not directly linked with swimming performance. There was no strong evidence that force production is higher on the dominant side or that symmetry in force production affects performance. Despite the longer stroke cycle times when breathing, the breathing actions did not affect force production. Faster swimmers often produced higher maximum force values and, sometimes, higher mean force values.

Bone Mineral Content Distribution in Response to Long-term Training of Elite Rowers

BACKGROUND/AIM

Bone response to exercise depends on the type and size of the mechanical stimulus. In rowing, athletes are exposed to low mechanical but large compression loads mainly on the trunk. Thus, this study aimed to investigate the impact of rowing on total and regional bone quality and bone turnover parameters in elite rowing athletes vs. control subjects.

MATERIALS AND METHODS

Twenty world-class rowers and twenty active, but not athletic, men participated in the study. Bone mineral density (BMD) and body mineral content (BMC) were assessed by dual-energy X-ray absorptiometry (DXA). Bone turnover markers (OPG and RANKL) in serum were assessed by Elisa method.

RESULTS

The current research revealed no statistical difference in total bone mineral density (TBMD) and total body mineral content (TBMC) between elite-level rowers and control subjects. Nevertheless, Trunk BMC (p=0.02) and Trunk BMC/TBMC ratio (p=0.01) were significantly higher in rowers than those in the control group. In contrast, in the control group, the Lower limbs BMC/TBMC ratio (p=0.007) was statistically higher. Furthermore, RANKL (p=0.011) and OPG (p=0.03) were statistically significantly higher in rowers, whereas the OPG/RANKL ratio (p=0.012) was statistically higher in the control group.

CONCLUSION

Rowing, as a non-weight-bearing exercise, did not alter total bone density but induced a remarkable redistribution of bone density from the lower limbs to the trunk. In addition, the current evidence suggests that the underlying molecular mechanism is based on turnover of intermediates, rather than solely bone redistribution.

Contribution of select physiological variables to sprint triathlon performance

BACKGROUND

The purpose of this study was to examine the relationship between select physiological variables and sprint triathlon performance.

METHODS

Moderately trained male triathletes (N.=15) performed two graded maximal exercise tests, on a cycle ergometer and a treadmill. Anaerobic capacity was evaluated, on a cycle ergometer and a treadmill. Within two weeks before or after the testing, all triathletes participated in a sprint triathlon race (750 m sea swim, 20 km cycle, 5 km run).

RESULTS

The results showed that significant correlations exist between VO2max during cycling (r=-0.811, P<0.05) or running (r=-0.757, P<0.05) and overall triathlon performance. Stepwise multiple linear regression analysis, with triathlon performance as the dependent variable and the physiological measures during running as the independent variables, showed that VO2max (mL.min-1.kg-1), Time_CF, CHO_rate @ VT and % body fat yielded the best prediction of performance (R2=0,912). When only the physiological variables from cycling were included into the model, the results showed that VO2max (mL.min-1), VO2max (mL.min-1.kg-1) and PFmax (rpm) explained 88% of the variation in sprint triathlon performance.

CONCLUSIONS

Our data indicate that overall race time for moderately trained triathletes, competing over the sprint distance can be accurately predicted from maximal laboratory tests.

Cardiorespiratory responses and reduced apneic time to cold-water face immersion after high intensity exercise

Apnea after exercise may evoke a neurally mediated conflict that may affect apneic time and create a cardiovascular strain. The physiological responses, induced by apnea with face immersion in cold water (10 °C), after a 3-min exercise bout, at 85% of VO2max,were examined in 10 swimmers. A pre-selected 40-s apnea, completed after rest (AAR), could not be met after exercise (AAE), and was terminated with an agonal gasp reflex, and a reduction of apneic time, by 75%. Bradycardia was evident with immersion after both, 40-s of AAR and after AAE (P<0.05). The dramatic elevation of, systolic pressure and pulse pressure, after AAE, were indicative of cardiovascular stress. Blood pressure after exercise without apnea was not equally elevated. The activation of neurally opposing functions as those elicited by the diving reflex after high intensity exercise may create an autonomic conflict possibly related to oxygen-conserving reflexes stimulated by the trigeminal nerve, and those elicited by exercise.

Influence of developmental and hormonal factors on bone health in adolescent females: a cross-sectional study and review of the literature

OBJECTIVE

To study bone density in healthy Greek girls going through puberty and determine the influence of developmental and hormonal factors.

DESIGN

Sixty healthy female adolescents (average age of 13.88±2.53 years) were included. Bone mineral density (BMD) was measured at the hip by DXA (dual energy X-ray absorptiometry). Pubertal stage was determined by Tanner's criteria. Creatinine, calcium, phosphorus, parathyroid hormone, calcitonin and 25-OH-vitamin D levels were measured in blood samples. The European physical fitness test battery (EUROFIT) was used to assess the parameters of physical fitness that are related to strength.

RESULTS

Adolescent girls had a mean (±SD) BMD value of 0.947±0.144 g/cm2 at the total hip (total hip BMD). Tanner's stage for pubic hair and body mass index (BMI) constituted significant, positive and independent predicting factors for bone density of total hip. Deficiency of 25OH-vitamin D was a negative predicting factor of bone density. Blood levels of calcium and phosphorus, the hours that adolescents devoted to sports, and handgrip strength, were independent predicting factors of bone density at the hip.

CONCLUSIONS

Bone density and consequently bone health is determined by factors that can be modified in order to achieve optimal bone growth and reduce the risk of fractures and osteoporosis in later life.

Effect of dietary carbohydrate content on blood glucose levels of swimmers during training

AIM

Data, as far as the impact of carbohydrate content of diets on training performance, are limited and conflicting and blood glucose levels during swimming training have never been reported. The purpose of this study was to determine if the type of diet can influence blood glucose levels during a regular swimming training session.

METHODS

Twelve elite male swimmers with a mean age of 15.7+/-0.67 years were enrolled for this study. Prior to testing, the swimmers were subjected to: 1) body composition analysis, 2) maximal heart rate determination, and 3) estimation of resting and swimming energy expenditure. Subsequently, swimmers were put on two isocaloric three-day diets, containing either a high percentage of carbohydrate (HCD-65%) or a low percentage of carbohydrate (LCD-35%) before performing the two 110 minutes training sessions (inter-spaced by 6-8 days) at an intensity of 75% of peak heart rates. Blood glucose was collected and analyzed at 0, 20, 60 and 110 minutes of exercise.

RESULTS

Blood glucose under both dietary conditions initially dropped and thereafter rose again by the end of the 110 minute training session. The data revealed that blood glucose never dropped to hypoglycemic levels, but showed a different pattern of changes throughout training.

CONCLUSION

The carbohydrate content of the diet followed for a period of three days prior to testing, does not appear to directly affect blood glucose levels throughout a swimming training session lasting over 90 minutes, in elite national level swimmers.