Comparison of ground reaction force asymmetry in one- and two-legged countermovement jumps.

This study examined whether ground reaction force (GRF) asymmetry of 2-legged countermovement jumps (CMJ) is related to 1-legged CMJ asymmetry. The GRF asymmetry of a 2-legged CMJ has been suggested as a preferred test to the 1-legged CMJ for functional strength and power deficit assessment. Twenty-eight men and 30 women performed 5 trials each of a 1-legged CMJ with the right limband the left limb, and a 2-legged CMJ. Vertical GRFs were collected from each lower limb using 2 force platforms. Although several GRF variables were calculated, vertical impulse correlated most strongly with jump height in all conditions (p < 0.05), and they were used in subsequent analyses. A moderate correlation was found for impulse asymmetry between the 1- and 2-legged CMJs for women (r = 0.45, p < 0.05), but not for men (r = 0.06, p = 0.76). In contrast, cross-tabulation analyses of subjects presented with the same dominant characteristics in the 1- and 2-legged CMJs revealed poor associations for both men (Freeman-Halton exact p = 0.61) and women (Freeman-Halton exact p = 0.19). Only 11 women recorded the same dominant limb for both 1- and 2-legged CMJs. This suggests that impulse asymmetries found in the 1- and 2-legged CMJ were unrelated. As the 1-legged CMJ relies on the extension forces generated entirely from 1 limb, variations in jump heights and GRF impulses by left and right limbs separately were more indicative of functional strength differences between sides. Hence, it is recommended that the 1-legged CMJ is used when examining functional strength asymmetry in the lower limbs. In contrast, factors causing asymmetry in GRF impulses during 2-legged CMJs are more complicated and require further investigation.

Kinanthropometric differences between 1997 World championship junior elite and 2011 national junior elite triathletes.

OBJECTIVES: In 1997, anthropometry measures were made to determine the body size and shapes of both senior and junior elite triathletes. Since then, the junior event distance has changed and the optimal morphology of participants may have evolved. Thus the objective of this study was to compare the morphology of 1997 World championship junior elite triathlon competitors with junior elite competitors in 2011. DESIGN: Comparative study of junior elite triathlete kinanthropometry. METHODS: Twenty-nine males and 20 females junior elite competitors in the 1997 Triathlon World Championships underwent 26 anthropometric measurements. Results were compared with 28 male and 14 female junior elite triathletes who competed in the 2011 Australian National Junior Series, as qualifying for 2011 Triathlon World Championships. Comparisons were made on the raw scores, as well as somatotype, and body proportional scores. RESULTS: Both male and female junior elite triathletes in the 2011 group were significantly more ectomorphic than their 1997 counterparts. The 2011 triathletes were also proportionally lighter, with significantly smaller flexed arm and thigh girths, and femur breadths. The 2011 males recorded significantly longer segmental lengths and lower endomorphy values than the 1997 junior males. CONCLUSIONS: Junior elite triathlete morphology has evolved during the past 14 years possibly as a result of changing race distance and race tactics, highlighting the importance of continually monitoring and updating such anthropometric data.

Cadence, Stride Rate and Stride Length during Triathlon Competition.

Triathlon research shows cycling alters the physiological response of subsequent running but, at present, biomechanical changes are unresolved. This study examined cycling cadence and running stride rate (SR) and length (SL) used by senior elite triathletes during competition. These variables were then compared to running and triathlon performance. Data from 51 elite male World Championships triathletes were analyzed via video recordings and Video Expert II Coach. Triathletes revealed consistent cadences throughout the majority of the cycle (96.8 +2.7 rpm) and run (90.9 +2.4 rpm) disciplines. However, a cadence increase (99.6 +5.7 rpm) was recorded at the completion of the cycle prior to running. Running SR and SL was significantly lower at the end of the run indicating a level of fatigue (p<0.01). Running SL was significantly and positively correlated with running and triathlon performance (p<0.01) suggesting those that could maintain a longer SL had a faster run and better final finishing position.

Short and long-term adherence to swimming and walking programs in older women--the Sedentary Women Exercise Adherence Trial (SWEAT 2).

OBJECTIVE: To examine in previously sedentary older women the effects of exercise mode and a behavioural intervention on short and long-term retention and adherence. METHODS: Healthy, sedentary women aged 50-70 years (N=116) were randomly assigned to a supervised 6-month swimming or walking program 3 sessions a week. They were further randomised to usual care or a behavioural intervention. The same program was further continued unsupervised for 6 months. We assessed retention, adherence, stage of exercise behaviour and changes in fitness. RESULTS: One hundred women (86%) completed 6 months and 86 (74%) continued for 12 months. Retention rates were similar for both exercise modes at 6 and 12 months. Adherence to swimming or walking was similar after 6 months (76.3 (95% CI: 69.5, 83.1)% vs. 74.3 (67.7, 80.9)%) and 12 months (65.8 (57.9, 73.8)% vs. 62.2 (54.6, 70.0)%). The behavioural intervention did not enhance retention or adherence. Fitness improved for both exercise modes after 6 months and was maintained at 12 months. CONCLUSIONS: Either swimming or walking programs initiated with careful supervision over 6 months resulted in similar high retention and adherence rates by highly motivated older women over 12 months. Behavioural intervention in this setting did not improve these rates further.

Swim Positioning and its Influence on Triathlon Outcome.

Questions have been raised regarding which of the three legs of a triathlon influences the final finishing position. Some coaches subjectively believe that the swim and run are more important than the cycle, especially since the introduction of drafting during the cycle. This study analysed race position shifts between each of the three disciplines to assess the importance of the swim finish position and final finish position during draft legal Olympic distance triathlon events. Ten male and 10 female triathlon world cup events during one season were analysed. The results suggested that the triathlon swim leg is important because the winner exited the water in the first pack in 90% of elite male and 70% of elite female races. Correlations were also derived from finishing order for the whole triathlon and a finishing order that included the swim only, cycle only or run only time. For men, the average correlations for final finishing order with each of the swim, cycle and run, respectively, were 0.49, 0.67 and 0.86 and for the women; average correlations were 0.39, 0.67 and 0.85. Hence, this indicated that it was important to exit the water in the first pack and run well after cycling to achieve a successful final finishing position.

Maternal physiological responses to swimming training during the second trimester of pregnancy.

Maternal submaximal aerobic fitness (PWC170) was measured before, during, and after 12 weeks of swimming training during the second trimester of pregnancy in 23 sedentary women. For comparison, 11 women maintained their normal activities, but did not swim. Training sessions were 3 times per week for 40 min, producing heart rate (HR) responses of 65%-70% of estimated maximum HR and increases in rectal temperature (n = 8) of approximately 0.4 degrees C. Distance swum per session almost doubled over the training period (581 +/- 177 m to 1110 +/- 263 m). PWC170 of the nonswimming group remained stable over time; that of the swimming group increased significantly by 13.8% after 8 weeks of training (790 +/- 145 to 909 +/- 137 kpm/min; p = 0.026). The results indicate that a significant aerobic training effect can be achieved by light-moderate-intensity swimming during pregnancy in previously sedentary women. Further, all women remained healthy, with no adverse outcomes for mother or baby.

Blood pressure rise with swimming versus walking in older women: the Sedentary Women Exercise Adherence Trial 2 (SWEAT 2).

OBJECTIVE: Swimming is often recommended in the prevention and treatment of hypertension. Few studies have investigated the effect of swimming training on blood pressure (BP). Our objective was to evaluate 6 months of supervised moderate swimming or walking on BP in previously sedentary, normotensive, older women. DESIGN: Women aged 50-70 years (n = 116) were randomly assigned to a supervised 6-month swimming or walking programme. They were further randomized to receive usual care or a behavioural intervention package. METHODS: Exercise comprised 3 sessions/week with a warm-up, cool down, and 30-min of moderate intensity walking or swimming. BP was recorded for 20 min supine, and 5 min standing. Assessments were made at 0 and 6 months. RESULTS: At baseline, mean supine BP (+/- SD) was 115.7 +/- 1.3/66.8 +/- 0.7 mmHg. Swimming improved swim distance by 78.1 m (29.3%) [95% confidence interval (CI); 66.7, 89.4] and walk time by 0.58 min (3.8%) (0.41, 0.74). Walking decreased walk time by 1.0 min (6.5%) (0.81, 1.19). After adjustment for initial BP, age, hypertension treatment status and change in weight, swimming increased supine and standing systolic BP relative to walking by 4.4 mmHg (1.2, 7.5) (P = 0.008) and 6.0 mmHg (2.6, 9.5) (P = 0.001), respectively. Supine and standing diastolic BP increased by 1.4 mmHg (-0.14, 3.0) (P = 0.07) and 1.8 mmHg (-0.02, 3.5) (P = 0.05), respectively. CONCLUSION: Relative to moderately paced walking, regular swimming significantly elevates BP in previously sedentary, normotensive, older women. This finding may have important implications for exercise prescription in older subjects.

Effects of 4 weeks of creatine supplementation in junior swimmers on freestyle sprint and swim bench performance.

To determine whether 4 weeks of oral creatine (Cr) supplementation could enhance single freestyle sprint and swim bench performance in experienced competitive junior swimmers, 10 young men and 10 young women (x age = 16.4 +/- 1.8 years) participated in a 27-day supplementation period and pre- and posttesting sessions. In session 1 (presupplementation testing), subjects swam one 50-m freestyle and then (after approximately 5 minutes of active recovery) one 100-m freestyle at maximum speed. Blood lactate was measured before and 1 minute after each swim trial. Forty-eight hours later, height, mass, and the sum of 6 skinfolds were recorded, and a Biokinetic Swim Bench total work output test (2 x 30-second trials, with a 10-minute passive recovery in between) was undertaken. After the pretests were completed, participants were divided into 2 groups (n = 10, Cr; and n = 10, placebo) by means of matched pairs on the basis of gender and 50-m swim times. A Cr loading phase of 20 g x d(-1) for 5 days was then instituted, followed by a maintenance phase of 5 g x d(-1) for 22 days. Postsupplementation testing replicated the presupplementation tests. Four weeks of Cr supplementation did not influence single sprint performance in the pool or body mass and composition. However, 30-second swim bench total work scores for trial 1 and trial 2 increased after Cr (p < 0.05) but not placebo ingestion. Postexercise blood lactate values were not different after supplementation for the 50- and 100-m sprint trials either within or between groups. It was concluded that 4 weeks of Cr supplementation did not significantly improve single sprint performance in competitive junior swimmers, but it did enhance swim bench test performance.

Secular changes in the stature and mass of Western Australian secondary school children.

Anthropometric data for 4,683 Western Australian secondary school chidren from the metropolitan area of Perth, Western Australia, were compared with figures compiled in 1940 from the same area. In the 44 year period, the average stature of 12- to 18-year-old males increased by approximately 4% in each 1 year age band and average body mass increased by 15%. Over the same period, girls of similar age showed stature increases with a mean value of 2% for each 1 year age group and average mass increases of 11%. The magnitude of the secular increase declined with age from 12 to 17 years. Standard deviations for the 1940 data were not presented; hence, the statistical significance of any difference between mean values could not be established. The body mass index (BMI) estimates from 1940 were lower at all ages for both sexes than the actual BMI data from 1984. © 1995 Wiley-Liss, Inc.