Biomedical subjects

R Dyson

Publications and source records attributed to R Dyson.

At least 19 recordsLinked to original sources

PubMed2001

The effects of restricted energy and fluid intake on simulated amateur boxing performance.

This study examined the effects of serial reductions in energy and fluid intake on two simulated boxing performances separated by 2 days recovery. Eight amateur boxers (age: 23.6 +/- 3.2 years; height 175 +/- 5 cm; body mass [BM] 73.3 +/- 8.3 kg [Mean +/- SD]) performed two simulated boxing bouts (BB) under normal (N-trial) and restricted (R-trial) diets in a counterbalanced design over 5 days. The trials were separated by a 9-day period of normal dietary behavior (X-trial). BM was recorded on days 1, 3, and 5 of each trial. Simulated bouts of three, 3-min rounds with 1-min recovery were completed on days 3 (BB1) and 5 (BB2) of each 5-day trial. Punching force (N) was recorded from 8 sets of 7 punches by a purpose-built boxing ergometer. Heart rate (fC) was monitored continuously (PE3000 Polar Sports Tester, Kempele, Finland), and blood lactate (BLa) and glucose (BG) were determined 4-min post-performance (2300 StaPlus, YSI, Ohio). Energy and fluid intakes were significantly lower in the R-trial (p < .05). Body mass was maintained during the N-trial but fell 3% (p < .05) during the R-trial. There were no significant differences in end-of-bout fC or post-bout BG, but BLa was higher in the N- than the R-trial (p < .05). R-trial punching forces were 3.2% and 4.6% lower, respectively, compared to the corresponding N-trial bouts, but the differences did not reach statistical significance. These results suggest that energy and fluid restrictions in weight-governed sports do not always lead to a significant decrease in performance, but because of the small sample size and big variations in individual performances, these findings should be interpreted with care.

Adult↗

PubMed2000

Dioxygen-binding kinetics and thermodynamics of a series of dicopper(I) complexes with bis[2-(2-pyridyl)ethyl]amine tridendate chelators forming side-on peroxo-bridged dicopper(II) adducts.

Copper-dioxygen interactions are of interest due to their importance in biological systems as reversible O2- carriers, oxygenases, or oxidases and also because of their role in industrial and laboratory oxidation processes. Here we report on the kinetics (stopped-flow, -90 to 10 degrees C) of O2-binding to a series of dicopper(I) complexes, [Cu2(Nn)(MeCN)2]2+ (1Nn) (-(CH2)n- (n = 3-5) linked bis[(2-(2-pyridyl)ethyl]amine, PY2) and their close mononuclear analogue, [(MePY2)Cu(MeCN)]+ (3), which form mu-eta 2:eta 2-peroxodicopper(II) complexes [Cu2(Nn)-(O2)]2+ (2Nn) and [(MePY2)Cu]2(O2)]2+ (4), respectively. The overall kinetic mechanism involves initial reversible (k+,open/k-,open) formation of a nondetectable intermediate O2-adduct [Cu2(Nn)(O2)]2+ (open), suggested to be a CuI...CuII-O2- species, followed by its reversible closure (k+,closed/k-,closed) to form 2Nn. At higher temperatures (253 to 283 K), the first equilibrium lies far to the left and the observed rate law involves a simple reversible binding equilibrium process (kon,high = (k+,open/k-,open)(k+,closed)). From 213 to 233 K, the slow step in the oxygenation is the first reaction (kon,low = k+,open), and first-order behavior (in 1Nn and O2) is observed. For either temperature regime, the delta H++ for formation of 2Nn are low (delta H++ = -11 to 10 kJ/mol; kon,low = 1.1 x 10(3) to 4.1 x 10(3) M-1 s-1, kon,high = 2.2 x 10(3) to 2.8 x 10(4) M-1 s-1), reflecting the likely occurrence of preequilibria. The delta H degree ranges between -81 and -84 kJ mol-1 for the formation of 2Nn, and the corresponding equilibrium constant (K1) increases (3 x 10(8) to 5 x 10(10) M-1; 183 K) going from n = 3 to 5. Below 213 K, the half-life for formation of 2Nn increases with, rather than being independent of, the concentration of 1Nn, probably due to the oligomerization of 1Nn at these temperatures. The O2 reaction chemistry of 3 in CH2Cl2 is complicated, including the presence of induction periods, and could not be fully analyzed. However, qualitative comparisons show the expected slower intermolecular reaction of 3 with O2 compared to the intramolecular first-order reactions of 1Nn. Due to the likelihood of the partial dimerization of 3 in solution, the t1/2 for the formation of 4 remains constant with increasing complex concentration rather than decreasing. Acetonitrile significantly influences the kinetics of the O2 reactions with 1Nn and 3. For 1N4, the presence of MeCN inhibits the formation of a previously (Jung et al, J. Am. Chem. Soc. 1996, 118, 3763-3764) observed intermediate. Small amounts of added MeCN considerably slow the oxygenation rates of 3, inhibit its full formation to 4, and increase the length of the induction period. The results for 1Nn and their mononuclear analogue 3 are presented, and they are compared with each other as well as with other dinucleating dicopper(I) systems.

Copper↗

PubMed2000

The effects in humans of rapid loss of body mass on a boxing-related task.

The physiological effects of strategies for a rapid loss of body mass immediately before weighing-in for competition in weight-governed sports are unclear. This study examined the effects of a 3%-4% loss in body mass on a boxing-related task. Seven novice amateur boxers completed three 3 min rounds of simulated boxing on a prototype boxing ergometer in an euhydrated state (E-trial) and after exercise-induced thermal dehydration (D-trial). All subjects lost body mass following dehydration-mean body mass fell 3.8 (SD +/- 0.3)% [77.3 (SD +/- 11.3) to 74.4 (SD +/- 10.7) kg, P<0.001] - but changes in plasma volume (PV) were inconsistent. Four subjects suffered reductions in PV between 15% and 30%, one subject maintained his E-trial value and two recorded an increase. The D-trial mean PV value was 8.0 (SD +/- 17.2)% lower but this fall was not statistically significant (P>0.05). Analysis of D-trial boxing performance showed one subject maintained his performance over the two trials and a second improved 17.8%. A two-way ANOVA (condition x time) with repeated measures on both factors showed no significant main effect differences for condition (F1,6 = 3.93 P>0.05), time (F1.83,48 = 1.12, P>0.05) or interaction between them (F1.93,48, P>0.05). Furthermore, neither heart rate nor blood lactate responses in the boxing task differed between trials. These data were affected by the small sample. Power and effect size analysis using eta(2) procedure and removing the outlier data produced a mean fall in boxing performance of 26.8%. However, some subjects appeared able to resist the deleterious effects of a rapid loss of body mass prior to competition and further research is needed to explain the mechanisms under-pinning this ability.

Adult↗

PubMed2000

Simultaneous measurement of back and front foot ground reaction forces during the same delivery stride of the fast-medium bowler.

Six male cricket bowlers (mean +/- s(mean): age 23.5 +/- 1.3 years; height 1.83 +/- 0.04 m; body weight 826 +/- 20 N) performed their typical bowling action at a set of stumps positioned at standard pitch length (20.1 m). A specially designed force platform rig allowed the correct positioning of two force platforms to be achieved beneath an outdoor polyflex runway (0.017 m depth) for each player's delivery stride pattern. For the back foot, the peak vertical ground reaction force was 1.95 +/- 0.08 kN (2.37 +/- 0.14 BW) and the braking force was 0.77 +/- 0.12 kN (0.94 +/- 0.16 BW). For the front foot, the peak vertical force was 4.80 +/- 0.92 kN (5.75 +/- 0.98 BW) and the braking force was 2.93 +/- 0.56 kN (3.54 +/- 0.67 BW). The mean peak vertical loading rate for front foot contact was 205 +/- 52.8 kN x s(-1) (249 +/- 64 BW x s(-1)) with mean values ranging from 81 to 446 kN x s(-1) (98 to 540 BW x s(-1)). The range for back foot contact was much smaller, 25-70 kN x s(-1) (30-85 BW x s(-1)), with a mean of 41.7 +/- 7.10 kN x s(-1) (50.6 +/- 8.6 BW x s(-1)). Mean peak impact occurred 24 ms after touchdown for the back foot and 16 ms after touchdown for the front foot. At impact, mean peak loading rates were greater for the front foot at 246 kN x s(-1) (298 BW x s(-1)), with a range of 80-483 kN x s(-1) (98-534 BW x s(-1)), than for the back foot at 65 kN x s(-1) (79 BW x s(-1)), with a range of 40-84 kN x s(-1) (49-110 BW x s(-1)).

Adult↗

PubMed2000

Effects of massage on physiological restoration, perceived recovery, and repeated sports performance.

BACKGROUND: Despite massage being widely used by athletes, little scientific evidence exists to confirm the efficacy of massage for promoting both physiological and psychological recovery after exercise and massage effects on performance. AIM: To investigate the effect of massage on perceived recovery and blood lactate removal, and also to examine massage effects on repeated boxing performance. METHODS: Eight amateur boxers completed two performances on a boxing ergometer on two occasions in a counterbalanced design. Boxers initially completed performance 1, after which they received a massage or passive rest intervention. Each boxer then gave perceived recovery ratings before completing a second performance, which was a repeated simulation of the first. Heart rates and blood lactate and glucose levels were also assessed before, during, and after all performances. RESULTS: A repeated measures analysis of variance showed no significant group differences for either performance, although a main effect was found showing a decrement in punching force from performance 1 to performance 2 (p<0.05). A Wilcoxon matched pairs test showed that the massage intervention significantly increased perceptions of recovery (p<0.01) compared with the passive rest intervention. A doubly multivariate multiple analysis of variance showed no differences in blood lactate or glucose following massage or passive rest interventions, although the blood lactate concentration after the second performance was significantly higher following massage (p<0.05). CONCLUSIONS: These findings provide some support for the psychological benefits of massage, but raise questions about the benefit of massage for physiological restoration and repeated sports performance.

Adult↗

PubMed1998

Effects of monensin on the reproduction, health, and milk production of dairy cows.

A randomized clinical trial including 1109 cows from 12 Australian dairy herds was used to evaluate the effects of monensin on the health (n = > 686 cows), production (n = 915 cows), and reproduction (n = > 908 cows) of dairy cows. Cows were allocated to a treatment group receiving a slow-release intraruminal bolus containing 32 g of sodium monensin that was administered 40 d before and 50 d following the anticipated calving date or to a control group. Treatment did not significantly alter any reproductive outcome; 54.5% of cows treated with monensin and 58.2% of control cows were pregnant at first service, and days to conception were lower for cows treated with monensin. The hazard rate (0.95) was not significant for these cows. The percentage of cows pregnant was 83.8 for control cows, and days to first estrus (hazard rate = 1.04) and first service (hazard rate = 1.04) were not significantly higher for treated cows. Treatment with monensin did not significantly alter the risk of any disease. The incidence of retained fetal membranes, pyometra, lameness, abortion, and infectious diseases was not significantly lower for cows in the treatment group, and the incidence of mastitis was not significantly higher for cows in the treatment group. Monensin significantly increased milk production by 0.75 L/d per cow and tended to increase milk fat and protein yields but had no significant effect on milk fat or milk protein percentages. Changes in the production of milk and milk constituents were consistent throughout lactation.

Animals↗

PubMed1994

Effects of sodium monensin on reproductive performance of dairy cattle. I. Effects on conception rates, calving-to-conception intervals, calving-to-heat and milk production in dairy cows.

A total of 1061 lactating dairy cows in six different herds were randomly allocated to treatment and control groups. One herd was lot-fed on total mixed rations; three herds were fed on pasture with significant amounts of supplementary concentrates, and two herds were primarily pasture fed. Treated cows received a slow-release, intraruminal capsule containing 32 g sodium monensin within 7 days of calving. Conception rates at first service, days to first oestrus and calving-to-conception interval did not differ significantly between untreated and monensin-treated cows in the 5 herds, 3 herds and 4 herds, respectively, in which these outcomes were examined. Treatment of lactating cows immediately after calving may not be the optimal method to achieve fertility responses with capsules containing sodium monensin. Monensin treatment significantly increased milk yield in one of the six herds. Milk fat or milk protein production was not significantly affected by treatment.

Animals↗

PubMed1990