Fit of bicycle safety helmets and risk of head injuries in children.
(33/1075)
BACKGROUND: Although bicycle helmets are effective in preventing head and brain injury, some helmeted individuals nevertheless sustain head injury. One of the possible reasons may be poor fit of the helmet on the head. This study was undertaken to examine the relationship between helmet fit and risk of injury. METHODS: 1718 individuals who were helmeted riders in a crash were queried on helmet fit and position. A sample of 28 children 2-14 years of age who sustained a head injury while wearing a bicycle helmet and 98 helmeted individuals of the same age treated in the same hospital emergency departments for injuries other than to the head, underwent anthropometric measurements of helmet fit. Measurements were made of the child's head, the helmet, and on a cast made of the child's head. RESULTS: Individuals whose helmets were reported to fit poorly had a 1.96-fold increased risk of head injury compared with those whose helmets fit well. Children with head injuries had helmets which were significantly wider than their heads compared with children without head injuries. Helmet fit was poorer among males and among younger children. CONCLUSIONS: Poor fit of helmets may be associated with an increased risk of head injury in children, especially in males. Helmets may not be designed to provide optimal protection. (+info)
A comparison of the effect of different bicycle helmet laws in 3 New York City suburbs.
(34/1075)
OBJECTIVES: This study was conducted to evaluate the effectiveness of 3 different bicycle helmet laws. METHODS: A direct observational study of nearly 1000 cyclists at 20 matched sites in each of 3 contiguous counties--Rockland and Westchester in New York and Fairfield in Connecticut--was carried out. Rockland's bicycle helmet law requires approved helmets for all cyclists regardless of age; Westchester's, by state law, requires cyclists younger than 14 years to wear helmets; and Fairfield's, also by state law, requires cyclists younger than 12 years to wear helmets when riding on highways. RESULTS: Rockland cyclists had the highest helmet use rate (35%), followed by Westchester (24%) and Fairfield (14%) cyclists. As a subgroup, teenagers used helmets least, a trend that was seen in all 3 counties. CONCLUSIONS: Our study suggests a positive effect of bicycle helmet legislation with no age limitation. (+info)
Exercise training increases basal nitric oxide production from the forearm in hypercholesterolemic patients.
(35/1075)
The objective of this study was to investigate the effects of cycle training on basal nitric oxide (NO) production and endothelium-dependent dilator capacity in hypercholesterolemic patients in whom acetylcholine responsiveness is impaired. Nine sedentary hypercholesterolemic volunteers (total plasma cholesterol >6.0 mmol/L; 2 female) aged 44+/-3 years (mean+/-SEM) participated in the study. Subjects remained sedentary for 4 weeks and performed 4 weeks of home-based cycle training (3 x 30 minutes/week at 65% maximum oxygen consumption [VO(2)max]) in a randomized order. Arteriovenous nitrate/nitrite (NO(x)) gradient was assessed and plethysmography was used to measure the forearm blood flow responses to arterial infusions of acetylcholine, sodium nitroprusside, and N(G)mono methyl L-arginine. Training increased VO(2)max from 30.4+/-1.9 to 34.3+/-1.4 mL x kg(-1) x min(-1) (P=0.01). Intrabrachial diastolic blood pressure was reduced from 70+/-3 to 68+/-3 mm Hg (P=0.02) with training, whereas systolic pressure did not change. Plasma triglycerides and total, LDL, and HDL cholesterol were not different between interventions. In the sedentary state, there was a positive forearm arteriovenous difference in plasma NO(x) indicating net extraction (6.8+/-4.0 nmol x 100 mL(-1) x min(-1)), whereas in the trained state this difference was negative, indicating net production (-5.8+/-5.8 nmol x 100 mL(-1) x min(-1); P=0.03). N(G)mono methyl L-arginine, at a dose of 4 micromol/min, caused a greater vasoconstriction after training (79.6+/-3.4% versus 69.9+/-6.8%; P=0.05). Acetylcholine and sodium nitroprusside induced dose-dependent elevations in forearm blood flow that were unaffected by training. These data suggest that basal release of endothelium-derived NO is increased with 4 weeks of home based training in hypercholesterolemic patients, independently of lipid profile modification. This may contribute to the cardiovascular protective effects of exercise training, including reduced blood pressure. (+info)
Cerebral metabolic response to submaximal exercise.
(36/1075)
We studied cerebral oxygenation and metabolism during submaximal cycling in 12 subjects. At two work rates, middle cerebral artery blood velocity increased from 62 +/- 3 to 63 +/- 3 and 70 +/- 5 cm/s as did cerebral oxygenation determined by near-infrared spectroscopy. Oxyhemoglobin increased by 10 +/- 3 and 25 +/- 3 micromol/l (P < 0. 01), and there was no significant change in brain norepinephrine spillover. The arterial-to-internal-jugular-venous (a-v) difference for O(2) decreased at low-intensity exercise (from 3.1 +/- 0.1 to 2. 9 +/- 0.1 mmol/l; P < 0.05) and recovered at moderate exercise (to 3. 3 +/- 0.1 mmol/l). The profile for glucose was similar: its a-v difference tended to decrease at low-intensity exercise (from 0.55 +/- 0.05 to 0.50 +/- 0.02 mmol/l) and increased during moderate exercise (to 0.64 +/- 0.04 mmol/l; P < 0.05). Thus the molar ratio (a-v difference, O(2) to glucose) did not change significantly. However, when the a-v difference for lactate (0.02 +/- 0.03 to 0.18 +/- 0.04 mmol/l) was taken into account, the O(2)-to-carbohydrate ratio decreased (from 6.1 +/- 0.4 to 4.7 +/- 0.3; P < 0.05). The enhanced cerebral oxygenation suggests that, during exercise, cerebral blood flow increases in excess of the O(2) demand. Yet it seems that during exercise not all carbohydrate taken up by the brain is oxidized, as brain lactate metabolism appears to lower the balance of O(2)-to-carbohydrate uptake. (+info)
Pulmonary gas exchange during exercise in highly trained cyclists with arterial hypoxemia.
(37/1075)
The causes of exercise-induced hypoxemia (EIH) remain unclear. We studied the mechanisms of EIH in highly trained cyclists. Five subjects had no significant change from resting arterial PO(2) (Pa(O(2)); 92.1 +/- 2.6 Torr) during maximal exercise (C), and seven subjects (E) had a >10-Torr reduction in Pa(O(2)) (81.7 +/- 4.5 Torr). Later, they were studied at rest and during various exercise intensities by using the multiple inert gas elimination technique in normoxia and hypoxia (13.2% O(2)). During normoxia at 90% peak O(2) consumption, Pa(O(2)) was lower in E compared with C (87 +/- 4 vs. 97 +/- 6 Torr, P < 0.001) and alveolar-to-arterial O(2) tension difference (A-aDO(2)) was greater (33 +/- 4 vs. 23 +/- 1 Torr, P < 0. 001). Diffusion limitation accounted for 23 (E) and 13 Torr (C) of the A-aDO(2) (P < 0.01). There were no significant differences between groups in arterial PCO(2) (Pa(CO(2))) or ventilation-perfusion (VA/Q) inequality as measured by the log SD of the perfusion distribution (logSD(Q)). Stepwise multiple linear regression revealed that lung O(2) diffusing capacity (DL(O(2))), logSD(Q), and Pa(CO(2)) each accounted for approximately 30% of the variance in Pa(O(2)) (r = 0.95, P < 0.001). These data suggest that EIH has a multifactorial etiology related to DL(O(2)), VA/Q inequality, and ventilation. (+info)
Heart dimensions may influence the occurrence of the heart rate deflection point in highly trained cyclists.
(38/1075)
OBJECTIVES: To determine whether the heart rate (HR) response to exercise in 21 highly trained cyclists (mean (SD) age 25 (3) years) was related to their heart dimensions. METHODS: Before performing an incremental exercise test involving a ramp protocol with workload increases of 25 W/min, each subject underwent echocardiographic evaluation of the following variables: left ventricular end diastolic internal diameter (LVIDd), left ventricular posterior wall thickness at end diastole (LVPWTd), interventricular septal wall thickness at end diastole (IVSTd), left ventricular mass index (LVMI), left atrial dimension (LAD), longitudinal left atrial (LLAD) and right atrial (LRAD) dimensions, and the ratio of early to late (E/A) diastolic flow velocity. RESULTS: The HR response showed a deflection point (HRd) at about 85% VO2MAX in 66.7% of subjects (D group; n = 14) and was linear in 33.3% (NoD group; n = 7). Several echocardiographic variables (LVMI, LAD, LLAD, LRAD) indicative of heart dimensions were similar in each group. However, mean LPWTd (p<0.01) and IVSTd (p<0.05) values were significantly higher in the D group. Finally, no significant difference between groups was found with respect to the E/A. CONCLUSIONS: The HR response is curvilinear during incremental exercise in a considerable number of highly trained endurance athletes-that is, top level cyclists. The departure of HR increase from linearity may predominantly occur in athletes with thicker heart walls. (+info)
Effect of precooling on high intensity cycling performance.
(39/1075)
OBJECTIVE: To examine the effects of precooling skin and core temperature on a 70 second cycling power test performed in a warm and humid environment (29 degrees C, 80% relative humidity). METHODS: Thirteen male national and international level representative cyclists (mean (SD) age 24.1 (4.1) years; height 181.5 (6.2) cm; weight 75.5 (6.4) kg; maximal oxygen uptake (VO2peak) 66.1 (7.0) ml/kg/min) were tested in random order after either 30 minutes of precooling using cold water immersion or under control conditions (no precooling). Tests were separated by a minimum of two days. The protocol consisted of a 10 minute warm up at 60% of VO2peak followed by three minutes of stretching. This was immediately followed by the 70 second power test which was performed on a standard road bicycle equipped with 172.5 mm powermeter cranks and mounted on a stationary ergometer. RESULTS: Mean power output for the 70 second performance test after precooling was significantly (p<0.005) increased by 3.3 (2.7)% from 581 (57) W to 603 (60) W. Precooling also significantly (p<0.05) decreased core, mean body, and upper and lower body skin temperature; however, by the start of the performance test, lower body skin temperature was no different from control. After precooling, heart rate was also significantly lower than control throughout the warm up (p<0.05). Ratings of perceived exertion were significantly higher than the control condition at the start of the warm up after precooling, but lower than the control condition by the end of the warm up (p<0.05). No differences in blood lactate concentration were detected between conditions. CONCLUSIONS: Precooling improves short term cycling performance, possibly by initiating skin vasoconstriction which may increase blood availability to the working muscles. Future research is required to determine the physiological basis for the ergogenic effects of precooling on high intensity exercise. (+info)
Effect of changing the saddle angle on the incidence of low back pain in recreational bicyclists.
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OBJECTIVE: According to the literature, 30-70% of cyclists suffer from cervical, dorsal, or lumbar back pain. This study was conducted to evaluate one of the possible causes of low back pain and to suggest a solution by appropriate adjustments to the bicycle. METHODS: Serial fluoroscopic studies were performed while cyclists sat on different types of bicycle (sports, mountain, and city). Pelvic/spine angles were measured at different seat angles, and the related force vectors analysed. RESULTS: There was a tendency towards hyperextension of the pelvic/spine angle which resulted in an increase in tensile forces at the promontorium. These forces can easily be reduced by appropriate adjustment of the seat angle--that is, by creating an anterior inclining angle. The findings of the biomechanical analysis were then applied to a group of cyclists who were members of a cycling club and who complained of low back pain. After appropriate adjustment of the saddle angle, most of the cyclists (>70%) reported major improvement in the incidence and magnitude of their back pain. CONCLUSIONS: The incidence and magnitude of back pain in cyclists can be reduced by appropriate adjustment of the angle of the saddle. It is important that these findings be conveyed to cyclists, bicycle salesmen, trainers, and members of the general public who engage in cycling, in order to decrease the prevalence of back pain. (+info)