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Biomedical subjects

B A Blanksby

Publications and source records attributed to B A Blanksby.

At least 19 recordsLinked to original sources
PubMed2000

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.

Adult↗
PubMed2000

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.

Adult↗
PubMed2000

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.

Biomechanical Phenomena↗
PubMed1999

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.

Adolescent↗
PubMed1999

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.

Adolescent↗
PubMed1999

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.

Adult↗
PubMed1997

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.

Adult↗
PubMed1997

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.

Adult↗
PubMed1997

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.

Age Factors↗
PubMed1996

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.

Acetylcholine↗
PubMed1996

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.

Animals↗
PubMed1996

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.

Adult↗
PubMed1995

Beliefs and behaviour of general practitioners regarding promotion of physical activity.

To assess current practice, perceived desirable practice and barriers related to the promotion of physical activity in general practice, a questionnaire was developed and distributed to all 1228 general practitioners in Perth. From these, 789 valid returns were received (71 per cent response). The mean age of the respondents was 45 years, 69 per cent were male, 52 per cent had postgraduate qualifications and 73 per cent were in full-time practice. General practitioners most frequently asked patients about their current level of physical activity and discussed physical activity programs when seeing patients with symptoms of conditions that could benefit from exercise, rather than asking all patients, new patients or patients previously seen. Walking specifically for fitness was the activity most likely to be recommended. General practitioners felt more able to offer general advice than specific advice on physical activity. Lack of time was reported most frequently as a barrier to the promotion of physical activity (47 per cent), followed by insufficient educational materials (29 per cent), and preference of patients for drug treatment (27 per cent). There were significant differences between self-reports of current practice and perceived desirable practice in the promotion of physical activity by general practitioners. Future strategies should aim to increase the frequency of advice to patients with specific health conditions.

Attitude of Health Personnel↗
PubMed1995

The relationship between carbon dioxide sensitivity and sprint or endurance performance in young swimmers.

There has been some evidence that extremes of CO2 sensitivity can indicate an individual's potential for sprint or endurance athletic performance. This study examined the responses to CO2 rebreathing, and previously validated sprint and endurance tests by subjects who were involved in regular, but not intensive, swimming training. The aim was to determine whether subjects with low CO2 sensitivity might perform better on endurance tests, whilst those subjects with high CO2 sensitivity would be more successful in the sprint tests. Initially, 168 young (mean mean(s.d.) age = 12.4(2.1) years) swimmers were measured using a modified version of the Read CO2 rebreathing technique. From this sample, 17 high (mean means(s.d.) = 2.24(0.39) 1 min-1 mmHg-1) CO2 responders were matched by gender, age, height, weight and FVC with 17 low (mean means(s.d.) = 0.57(0.19) 1 min-1 mmHg-1) responders. Each of these 17 pairs underwent two sprint tests (10 s Tri-level alactic power, 50 m run) and two endurance tests (PWC170, 1.6 km run) in order to determine whether any differences existed between the two groups and the sprint and endurance parameters. The subjects remained unaware of their results of the rebreathing test throughout testing. A dependent t test was then used to compare the results collected from each group. The low CO2 responders recorded a significantly faster 1.6 km run time, but were not superior on the PWC170 ergometer test, than the high CO2 responders. The high CO2 responding group recorded significantly higher results on the 10 s alactic power test, but not the 50 m sprint run, than the low responders. Hence, further study is required to ascertain underlying causes as to why significant differences occurred with CO2 rebreathing, the 1.6 km run and the 10 s alactic power test, but not with the PWC170 and the 50m sprint run.

Adolescent↗
PubMed1995

The relationship of hypercapnic ventilatory responses to age, gender and athleticism.

When a gas mixture containing carbon dioxide (CO2) is inhaled by an individual, alveolar ventilation is increased. This ventilatory response to CO2 highlights the relationship between the increase in exercise ventilation and the increase in alveolar CO2 pressure (paCO2). This response is mediated centrally by brainstem chemoreceptors in the medulla and, to a lesser extent, peripherally by the carotid and aortic bodies. However, the response of increased breathing to rising paCO2 varies markedly among individuals. The responses to CO2 rebreathing have been investigated by a variety of research groups for different reasons. The range of responses by children and adults including: gender differences; responses by athletes; the relationship between age and body size; and whether it is an acquired or inherited response have been studied. The following is a summary of these different aspects of CO2 rebreathing has been complied to assist researchers studying any single or multiple facets of the area.

Adolescent↗
PubMed1995

Children's readiness for learning front crawl swimming.

This study attempted to establish whether an optimal age could be identified at which children were ready to learn the front crawl swimming stroke. The variables examined were: the number of lessons, the age of commencing lessons and the time duration for learning to swim 10m front crawl (Level 3). Longitudinal records of 326 children, aged between 2 and 8 years, were analysed using General Linear Model two-way (Age x Sex) analysis of variance procedures. The main effect for age was significant (p < 0.001) for all three variables. Post hoc analysis revealed that the children who started at 5 years of age received significantly fewer number of lessons and took shorter duration compared to those who commenced learning to swim at an earlier age. Whether pupils started lessons at 2, 3 or 4 years of age, they achieved Level 3 at approximately the same mean age of 5 1/2 years. The optimal readiness period was identified in this study to be between 5 and 6 years of age. There was little evidence of gender differences for all three variables.

Age Factors↗
PubMed1989

CO2 sensitivity changes during the menstrual cycle.

A study of the changes in CO2 sensitivity at rest was undertaken in 20 regularly menstruating females in an attempt to determine the influence of the menstrual cycle on this variable. A biphasic oral temperature graph was used to signify fertility and demarcate three phases of the cycle. A CO2-rebreathing test was conducted 3 times/wk for 6 wk to obtain CO2 sensitivity and CO2 threshold measures. An analysis of variance was used to compare the results collected in each phase of the cycle for each of the variables. A significant increase was found in the sensitivity to CO2 between the follicular and luteal phases, a significant decrease between the luteal and menstrual phases, and no significant difference between the follicular and menstrual phases. The change between follicular and luteal phases was attributed to the effect of progesterone, which is elevated during the luteal phase. No significant change was found in the CO2 threshold level.

Adolescent↗