Effectiveness and safety of a structured swimming program in previously sedentary women during pregnancy.

OBJECTIVE: To determine whether undertaking a swimming program in sedentary women during pregnancy would improve maternal fitness without adverse fetal consequences. METHODS: Prospective observational investigation of healthy sedentary pregnant women participating in a monitored swimming program. RESULTS: Twenty-three women attended swimming sessions from 16 to 28 weeks of gestation resulting in increasing distances swum and improved aerobic fitness as measured by physical work capacity (PWC170) (p = 0.003). Resting maternal heart rate decreased (p = 0.041) and resting systolic (p = 0.092) and diastolic (p = 0.971) blood pressures remained unchanged over gestation. The mean fetal heart rates decreased with advancing gestational age (p = 0.001), consistent with normal physiology. Non-stress tests and umbilical artery systolic/diastolic ratios were similar before and after swimming sessions, providing evidence that fetal well-being was unchanged. CONCLUSIONS: A structured swimming program in sedentary pregnant women increases maternal fitness without any alteration in maternal and fetal well-being.

Long term retention of safe diving skills.

This short report describes a 20-month follow-up of safe diving skills, extending the 8-month retention period previously published in this journal. Thirty-four recreational swimmers with poor diving skills were evaluated before and immediately after a diving skills intervention program. Twenty-two returned for the eight-month follow-up evaluation and 16 returned 20 months post. As with the earlier study, Treadwater, Deck, Block and Running dives were video-recorded, and maximum depth, distance, velocity, entry angle and flight distance were compared. Underwater hand and arm positions were examined. Pre-intervention, a breaststroke arm action before maximum depth occurred in 18% of all dives and 38% of Treadwater dives. This was eliminated post-intervention, improving head protection. The Treadwater dive elicited the greatest mean maximum depth, and ANOVA showed depth for this entry decreased (improved) following intervention and remained shallower at the eight-month and 20-month post follow-ups. The Block dive also became shallower following intervention while the Deck dive remained unchanged. As seven 10-minute skills sessions resulted in shallower dives with safer hand and arm positions, and these skills were retained over a 600 day non-practice period, it is reliable to consider that the inclusion of safe diving skills in learn-to-swim programs can provide a diving spinal cord injury prevention strategy.

Retention of safe diving skills.

This study investigated diving skill maintenance over an eight-month retention period following an intervention program. Thirty-four recreational swimmers with poor diving skills were measured before and immediately after a diving skills intervention program. Twenty-two returned for follow-up evaluation. Treadwater, Deck and Block dives were video-recorded, and maximum depth, distance, velocity, entry angle and flight distance were compared. Underwater hand and arm positions were examined. Pre-intervention, a breaststroke arm action before maximum depth occurred in 18% of all dives and 38% of Treadwater dives. This was eliminated post-intervention, improving head protection. The Treadwater dive elicited the greatest mean maximum depth, and ANOVA showed depth for this entry decreased (improved) following intervention and remained shallower at follow-up. Deck and Block dives also became shallower following intervention. As seven 10-minute skills sessions resulted in shallower dives with safer hand and arm positions, including safe diving skills in learn-to-swim programs can provide a diving spinal cord injury prevention strategy.

Comparison of buoyancy, passive and net active drag forces between Fastskin and standard swimsuits.

A cross-sectional comparison between the buoyancy, passive and net active drag force characteristics of full-length, Fastskin swimsuits with that of standard swimsuits was completed with nine Open National level swimmers (5 males and 4 females). Subjects were weighed in a hydrostatic tank and then towed via a mechanical winch on the surface and 0.4 m deep at 1.6, 2.2 and 2.8 m/s. The subjects performed a prone streamlined glide and maximum effort flutter kick at each towing velocity and depth. Hydrostatic weight differences between swimsuit types were not significant (p> 0.05. Fastskin passive drag values were significantly less than normal swimsuits during surface towing at 1.6 and 2.8 m/s: and at 0.4 m deep towing at 1.6, 2.2 and 2.8 m/s. Net active drag force values also were lower for the Fastskin suits when compared with those of normal swimsuits and a significant difference existed for surface towing at all three velocities of 1.6, 2.2 and 2.8 m/s. The full-length, Fastskin swimsuits created less total hydrodynamic resistance than normal swimsuits while providing no additional buoyancy benefits.

Risk reduction in diving spinal cord injury: teaching safe diving skills.

Thirty-four recreational swimmers underwent an intervention program to improve diving skills. Participants with low diving skills completed seven 10-minute sessions which emphasised locking thumbs and holding arms extended beyond the head, and steering and gliding skills. Various dive entries were video-recorded and maximum depth reached was used as the criterion measure. A one-way repeated measures analysis of variance was conducted for each dive condition. Maximum depth decreased for all dives. Velocity at maximum depth was greater for the Treadwater, Deck and Block conditions. Improved streamlining and increased 'spring' were evident in more confident participants. Hands separated in 71% of pre-intervention dives but only in 3% of post-intervention dives. Preintervention, arms were pulled backward before. or at, maximum depth in 30% of participants but none did this post-intervention. Diving skills were improved following participation in the intervention program.

Net forces during tethered simulation of underwater streamlined gliding and kicking techniques of the freestyle turn.

We assessed the net forces created when towing swimmers while gliding and kicking underwater to establish an appropriate speed for initiating underwater kicking, and the most effective gliding position and kicking technique to be applied after a turn. Sixteen experienced male swimmers of similar body shape were towed by a motorized winch and pulley system. A load cell measured net force (propulsive force - drag force) at speeds of 1.6, 1.9, 2.2, 2.5 and 3.1 m x s(-1). At each speed, the swimmers performed a prone streamline glide, a lateral streamline glide, a prone freestyle kick, a prone dolphin kick and a lateral dolphin kick. A two-way repeated-measures analysis of variance revealed significant differences between the gliding and kicking conditions at different speeds. The results demonstrated an optimal range of speeds (1.9 to 2.2 m x s(-1)) at which to begin underwater kicking to prevent energy loss from excessive active drag. No significant differences were found between the prone and lateral streamline glide positions or between the three underwater kicking techniques. Therefore, there appears to be no significant advantage in using one streamlining technique over another or in using one kicking style over another.

Morphology and performance of world championship triathletes.

Performance is related to body morphology in many sports. With triathlon making its debut into the Olympic programme in 2000, it was deemed important to determine which physical characteristics of elite-level triathletes were significantly related to performance. Seventy-one elite and junior elite triathletes, from 11 nations, competing at the 1997 World Triathlon Championships were measured on a battery of 28 anthropometric dimensions. A factor analysis was conducted, which reduced the number of variables to four and these were used in a stepwise linear regression to determine which morphological factors were important to performance. Elite triathletes were significantly (p < 0.05) faster than their junior counterparts (males 1:52:26 vs. 2:03:23 and females 2:07:01 vs. 2:14:05) and showed less variation in performance times. Run time variation was the largest of the component disciplines and tended to show the importance of this discipline to the final outcome. Following a factor analysis the four distinguishable morphological factors that emerged were: robustness, adiposity, segmental lengths and skeletal mass. Relating these factors to the total time obtained by the triathletes in this study yielded a regression equation that correlated significantly with all triathletes, accounting for 47% of the variance in total triathlon duration. The regression equations illustrated the importance of low levels of adiposity for elite triathletes for total time and most of the subdisciplines. The other factor that showed importance was that proportionally longer segmental lengths contributed to successful swimming outcome.

Endurance sports after total knee replacement: a biomechanical investigation.

PURPOSE: No biomechanical evaluation of total knee designs exists for loads occurring during sports activities. It was the purpose of the present study to evaluate the contact stress distribution and contact area of different knee joint designs for loads that occur during four common recreational endurance activities. METHODS: Three different total knee designs were evaluated for loads occurring during cycling (1.2 body weight (BW) at 80 degrees of knee flexion), power walking (4 BW at 20 degrees), hiking (8 BW at 40 degrees), and jogging (9 BW at 50 degrees) using Fuji pressure-sensitive film. The designs consisted of a flat tibial inlay, a curved inlay, and an inlay with mobile bearings. Five measurements were conducted for each load. The pressure sensitive films were scanned and analyzed using an image analysis program. RESULTS: During cycling, the area with stress levels above the yield point of polyethylene (overloaded area) was below 15 mm2 for each design. During power walking, the mobile bearing design showed no overloaded area, whereas it was below 50 mm2 for the flat and curved design. During downhill walking and jogging, more than 140 mm2 were overloaded for each design. CONCLUSIONS: It was concluded that patients after total knee replacement should alternate activities such as power walking and cycling. For mountain hiking, patients are advised to avoid descents or at least use ski poles. Jogging or sports involving running should be discouraged after total knee replacement.

The influence of plyometric training on the freestyle tumble turn.

This study examined the effects of a plyometric training program on freestyle tumble turns. Thirty-eight age group swimmers were assigned to a control group which swam 1.5 hours, three times per week for 20 weeks; or an experimental group which supplemented 1.25 hours of swimming with 15 minutes of plyometrics for the same time frame. The same coach conducted all swimming and plyometric sessions to ensure uniformity. Swimming performance was assessed from 50 m time. Freestyle turning performance was measured by 2.5 m round trip time (RTT), 5 m RTT, wall contact time and selected kinematic and kinetic variables associated with the turn. A Plyopower system was also used to test jump height and velocity. Repeated measures, multivariate analysis of variance showed no significant differences between the groups (pre-, mid- and post-intervention) over the period of the study for any swimming, kinetic or plyopower measures. Thus, equal benefits were derived from normal practice time in the water or land based plyometric exercises.

Characteristics of 'low risk' and 'high risk' dives by young adults: risk reduction in spinal cord injury.

STUDY DESIGN: To establish benchmark normative data for dive entries performed by young adults of the age range most likely to sustain a diving spinal cord injury. Data acquired from analysis of the dives performed, along with survey information, were used to determine which factors make the most contribution to the level of risk in diving. OBJECTIVES: To identify influential variables which could contribute to risk of spinal cord injury for each of four types of dives. The types of dives investigated were: dive entries from deck level to tread water (Treadwater); deck level to swim 25 m (Deck); starting block height to swim 25 m (Block); and a running dive entry to swim 25 m (Running). SETTING: Victoria, Australia. METHODS: Ninety-five first year university students (average age 19.9 years) performed three or four dives which were video-recorded for later analysis. Maximum depth reached was used as an indicator of risk, and velocity at maximum depth, distance at maximum depth, angle of entry and flight distance were measured for each dive. Participants also completed a questionnaire designed to elicit information about their swimming and diving background. Unlike previous diving studies, participants were recreational rather than competitive swimmers. They were not aware that the dive was the focal point, assuming that the researchers were investigating their swimming and treadwater ability. RESULTS: A stepwise multiple regression was applied to predict depth for each dive condition, and demonstrated that four variables were able to account for 56% of the variance for Treadwater, 68% for Deck; 73% for Running and 79% for Block. In all conditions involving swimming after the dive (ie Deck, Block and Running), beta weights showed that distance at maximum depth had the greatest influence on the depth of a dive. Flight distance and angle of entry were the next most influential variables. For the Treadwater condition, beta weights showed angle of entry was the most influential variable, followed by velocity at maximum depth, distance at maximum depth and swim rank. CONCLUSION: It is recommended that divers strive to surface in as short a distance as possible by maximising flight distance and aiming for a low entry angle. Implementation of steering-up techniques will assist in minimising dive depth.

Tailored advice on exercise--does it make a difference?

OBJECTIVE: A controlled trial to compare the effectiveness of verbal advice from a family physician (FP) combined with either "standard" or "tailored" written information on physical activity in increasing the levels of physical activity in sedentary patients. DESIGN: Sedentary patients (n = 763) were recruited through ten family practices and allocated to a control group or one of two intervention groups. Brief advice on physical activity was given by the FP during the consultation and either a standard or tailored pamphlet was mailed to the home address of patients assigned to the intervention groups within two days of their visit to the FP. RESULTS: The response to follow-up, via a postal survey at one, six, and twelve months after the index consultation was 70%, 60%, and 57%, respectively. Treating all nonresponders as sedentary, the results revealed that although more tailored subjects reported some physical activity at each follow-up compared with the standard group, these differences were not significant. Furthermore, there was no significant difference in movement across the stages of readiness to exercise at follow-up between subjects in the tailored group who received material targeting their current stage (precontemplation or contemplation) and the standard group who received generic material that addressed both stages. CONCLUSION: These findings do not concur with the results from previous research in the areas of nutrition and smoking cessation where additional benefits were seen with a tailored intervention. Future research on the application of the principles of "tailoring" to the promotion of physical activity should focus on identifying which, if any, physical, social, psychological or environmental variables should be addressed to produce improved outcomes over and above the effects of well designed generic materials.

How can and do Australian doctors promote physical activity?

BACKGROUND: Physical inactivity is recognized as an important public health issue. Yet little is known about doctors' knowledge, attitude, skills, and resources specifically relating to the promotion of physical activity. Our survey assessed the current practice, perceived desirable practice, confidence, and barriers related to the promotion of physical activity in family practice. METHODS: A questionnaire was developed and distributed to all 1,228 family practitioners in Perth, Western Australia. RESULTS: We received a 71% response (n = 789). Family practitioners are most likely to recommend walking to sedentary adults to improve fitness and they are aware of the major barriers to patients participating in physical activity. Doctors are less confident at providing specific advice on exercise and may require further skills, knowledge, and experience. Although they promote exercise to patients through verbal advice in the consultation, few use written materials or referral systems. CONCLUSIONS: There are significant differences between self-reports of current practice and perceived desirable practice in the promotion of physical activity by doctors. Future strategies need to address the self-efficacy of family physicians and involve resources of proven effectiveness. The potential of referral systems for supporting efforts to increase physical activity by Australians should be explored.

Effect of casting on forearm resistance vessels in young men.

The aim of this study was to determine whether physical deconditioning, induced by 6 wk of forearm casting, and the conditioning effects of recovery from casting would elicit changes in the response of forearm resistance vessels to substances that modulate vascular resistance. Forearm blood flow (FBF) responses to intrabrachial infusion of NGmonomethyl-L-arginine (LNMMA) and norepinephrine (NE) were examined in six subjects recovering from Colles', scaphoid, or metacarpal fractures within 72 h of cast removal and again after a 6-wk recovery period. Vascular responses were also examined in six noncasted controls. The FBF responses of casted and control subjects did not differ, and no changes occurred over the 6-wk study period. These results suggest that the effect of forearm casting and recovery from casting do not greatly influence control of vascular tone, including the basal activity of the NO dilator system in vivo.

Starting age and aquatic skill learning in young children: mastery of prerequisite water confidence and basic aquatic locomotion skills.

This study examined whether an optimal starting age emerged for acquiring water confidence (Level 1) or basic aquatic locomotion skills (Level 2). Analysis of 264 children between 2 and 7 years of age was made by examining numbers of lessons, age at reaching a given standard and the time duration required for each swim level. At 4 years of age, children demonstrated the ability to achieve the levels of water confidence and basic locomotion skills whereas earlier introduction to aquatic instruction did not translate into earlier mastery of these basic skills.

Aetiology and occurrence of diving injuries. A review of diving safety.

This paper examines multifaceted aspects of diving entries into water which are the cause of many critical injuries (costed at $A150 million) and therefore have important safety ramifications. Wedge and compression fractures are most commonly found in the cervical area of the spine with off-centre impacts with the pool or sea bottom. Diving-related injuries range from 2.3 in a South African study to 21% of spinal cord injuries in Poland. Alcohol and diving do not mix because of diminished awareness and information processing. Children aged under 13 years suffer fewer cervical injuries (1 to 4%), but complication rates are relatively high for this group. Sports trauma (diving-related in particular) is one of the more prevalent causes of spinal cord injury in children aged 6 to 15 years. The highest incidence occurs among those aged 10 to 14, followed by the group aged 5 to 9 years. This contradicts the common perception that 15-to 19-year-olds comprise the highest risk group. Boys are more frequently injured, and swimming pools are more common as an injury location then is the case with adults. The role played by water depth has been conclusively ascertained; technique, and therefore education, appear to be more important considerations in injury prevention. Although 89% of injuries occur in water < 1.52m, injuries are rare in water of 0.46 to 0.61m. Care with pool design to avoid sudden depth changes and the resultant "spinal wall' is necessary. Minimum depth values for diving vary from 1 to 1.52 m. Velocities and angles of entry are considered to ascertain the body's decelerative capacity upon entry. The scoop, racing start dive has been shown to require at least 1.22 m of water even when practised by trained divers; the risks involved must therefore be weighed against the fact that it may be no faster than more conventional dives. While it may be safe to perform kneeling and crouching dives into shallowers water, standing dives by untrained divers require a greater margin of error. Lack of education is an issue which needs to be addressed and this paper makes recommendations for safety practices such as steering up to the surface, head protection with the arms and only diving when absolutely necessary.

Safe depths for teaching children to dive.

Eight stages commonly used to teach diving were analysed for peak vertical velocity; vertical velocity at and following water impact and at previously recommended minimum water depths; maximum depth reached; and relationship between vertical velocity and maximum depth attained at each stage; for 13 male and 13 female children aged 6-8 years. Comparisons of mean water impact vertical velocities and maximum depths attained revealed significantly lower impact vertical velocities (F[6] = 117.39, p < 0.0001) and maximum depths (F[6] = 36.59, p < 0.0001) when performing the sit dive compared to the reference standing dive. At other stages, subjects travelled faster than the critical head velocities shown to cause adult cervical spine damage when passing through previously recommended minimum water depths.

Endothelium-derived nitric oxide activity in forearm vessels of tennis players.

The aim of this study was to determine whether physical conditioning induced by a repetitive exercise stimulus would elicit changes in the response of forearm resistance vessels to an infusion of substances that modulate nitric oxide synthesis. Forearm blood flow responses to a 5-min ischemic stimulus and intrabrachial infusion of acetylcholine, sodium nitroprusside, and NG-monomethyl-L-arginine were examined in the preferred and nonpreferred limbs of eight habitual tennis players. Forearm volume, girth, and grip strength were significantly greater in the preferred limb, indicating a bilateral difference in physical condition. This was associated with an enhanced reactive hyperemic response in the preferred limb (53.5 +/- 9.4 vs. 38.8 +/- 4.7 ml.100 ml-1.min-1; P < 0.05). No differences between the limbs were evident in response to acetylcholine, sodium nitroprusside, or NG-monomethyl-L-arginine. These results suggest that exercise training enhances the peak vasodilator capacity of the vasculature without influencing basal or stimulated activity of the nitric oxide dilator system in vivo.

Recreational patterns, body composition and socioeconomic status of Western Australian secondary school students.

A study of 4672 secondary school students was carried out in order to assess the relationship between body composition, recreational patterns, and socioeconomic status as indicated by parental occupation and the school attended. Results indicated that there were more girls than boys participating in organized sport, and health and fitness activities; and more boys than girls involved in informal recreational activities and home-based passive pursuits. A higher proportion of participants came from the higher socioeconomic status (SES) group. More high-SES students revealed weight appropriate to their height.

Control of skeletal muscle blood flow during dynamic exercise: contribution of endothelium-derived nitric oxide.

Traditional explanations for the hyperaemia which accompanies exercise have invoked the 'metabolic theory' of vasodilation, whereby contractile activity in the active muscle gives rise to metabolic by-products which dilate vessels bathed in interstitial fluid. Whilst metabolites with vasodilator properties have been identified, this theory does not adequately explain the magnitude of hyperaemia observed in active skeletal muscle, principally because large increases in flow are dependent on dilation of 'feed' arteries which lie outside the tissue parenchyma and are not subjected to changes in the interstitial milieu. Coordinated resistance vessel dilation during exercise is therefore dependent on a signal which 'ascends' from the microvessels to the feed arteries located upstream. Recent studies of ascending vasodilation have concentrated on the possible contribution of the endothelium, a monolayer of flattened squamous cells which lie at the interface between the circulating blood and vascular wall. These cells are uniquely positioned to respond to changes in rheological and humoral conditions within the cardiovascular system, and to transduce these changes into vasoactive signals which regulate blood flow, vascular tone and arterial pressure. Endothelial cells produce nitric oxide (NO), a rapidly diffusing labile substance which relaxes adjacent vascular smooth muscle. NO is released basally and contributes to the regulation of vascular tone by acting as a functional antagonist to sympathetic neural constriction. In addition, NO is spontaneously released in response to deformation of the endothelial cell membrane, indicating that changes in pulsatile flow and wall shear stress are likely physiological stimuli. Since the dilation of microvessels in response to exercise increases blood flow through the upstream feed arteries, which subsequently dilate, one explanation for ascending vasodilation is that NO release is stimulated by flow-induced shear stress. Evidence that NO contributes to ascending vasodilation is reviewed, along with studies which indicate that NO mediates exercise hyperaemia, that physical conditioning upregulates NO production and that NO controls blood flow by modifying other physiological mechanisms.