Biomedical subjects

Jeff S Coombes

Publications and source records attributed to Jeff S Coombes.

7 recordsLinked to original sources

PubMed2003

Optimising high-intensity treadmill training using the running speed at maximal O(2) uptake and the time for which this can be maintained.

The aim of this study was to compare the effects of two high-intensity, treadmill interval-training programs on 3000-m and 5000-m running performance. Maximal oxygen uptake (.VO(2max)), the running speed associated with .VO(2max) (v.VO(2max)), the time for which v.VO(2max) can be maintained (T(max)), running economy (RE), ventilatory threshold (VT) and 3000-m and 5000-m running times were determined in 27 well-trained runners. Subjects were then randomly assigned to three groups; (1) 60% T(max), (2) 70% T(max) and (3) control. Subjects in the control group continued their normal training and subjects in the two T(max) groups undertook a 4-week treadmill interval-training program with the intensity set at v.VO(2max) and the interval duration at the assigned T(max). These subjects completed two interval-training sessions per week (60% T(max)=six intervals/session, 70% T(max) group=five intervals/session). Subjects were re-tested on all parameters at the completion of the training program. There was a significant improvement between pre- and post-training values in 3000-m time trial (TT) performance in the 60% T(max) group compared to the 70% T(max) and control groups [mean (SE); 60% T(max)=17.6 (3.5) s, 70% T(max) =6.3 (4.2) s, control=0.5 (7.7) s]. There was no significant effect of the training program on 5000-m TT performance [60% T(max)=25.8 (13.8) s, 70% T(max)=3.7 (11.6) s, control=9.9 (13.1) s]. Although there were no significant improvements in .VO(2max), v.VO(2max) and RE between groups, changes in .VO(2max) and RE were significantly correlated with the improvement in the 3000-m TT. Furthermore, VT and T(max) were significantly higher in the 60% T(max) group post- compared to pre-training. In conclusion, 3000-m running performance can be significantly improved in a group of well-trained runners, using a 4-week treadmill interval training program at v.VO(2max) with interval durations of 60% T(max).

Adult↗

PubMed2003

Short-duration mechanical ventilation enhances diaphragmatic fatigue resistance but impairs force production.

STUDY OBJECTIVE: s: Mechanical ventilation (MV) is a life-support measure for patients who cannot maintain adequate alveolar ventilation. Following prolonged MV, difficulty in weaning patients from the ventilator can occur, and it has been postulated that difficult weaning is linked to respiratory muscle dysfunction. We tested the hypothesis that 18 h of controlled MV will diminish diaphragmatic maximal tetanic specific tension (force per cross-sectional area of muscle) without impairing diaphragmatic fatigue resistance. DESIGN: To test this postulate, adult Sprague-Dawley rats were randomly classified into one of two experimental groups: (1) control group (n = 8), and (2) 18-h MV group (n = 6). MV-treated animals were anesthetized, tracheostomized, and received room air ventilation. Animals in the control group were acutely anesthetized but did not receive MV. Muscle strips from the mid-costal diaphragm were removed from both experimental groups, and contractile properties were studied in vitro to determine the effects of MV on diaphragmatic endurance and maximal force production. Diaphragmatic endurance was investigated by measuring tension development during repeated contractions throughout a 30-min fatigue protocol. RESULTS: MV resulted in a reduction (p < 0.05) in diaphragmatic maximal specific tension (control group, 26.8 +/- 0.2 Newtons/cm(2) vs MV group, 21.3 +/- 0.6 Newtons/cm(2)). Compared to the control group, diaphragms from MV-treated animals maintained higher (p < 0.05) percentages of the initial force production throughout the fatigue protocol. The observed improvement in fatigue resistance was associated with an increase in diaphragmatic oxidative and antioxidant capacity as evidenced by increases (p < 0.05) in both citrate synthase and superoxide dismutase activities. However, by comparison to the control group, diaphragms from MV-treated animals generated less (p < 0.05) absolute specific force throughout the fatigue protocol. CONCLUSIONS: These data indicate that 18 h of MV enhances diaphragmatic fatigue resistance but impairs diaphragmatic specific tension.

Animals↗

PubMed2002

Effects of vitamin E deficiency on fatigue and muscle contractile properties.

Radical-mediated oxidative damage of skeletal muscle membranes has been implicated in the fatigue process. Vitamin E (VE) is a major chain breaking antioxidant that has been shown to reduce contraction-mediated oxidative damage. We hypothesized that VE deficiency would adversely affect muscle contractile function, resulting in a more rapid development of muscular fatigue during exercise. To test this postulate, rats were fed either a VE-deficient (EDEF) diet or a control (CON) diet containing VE. Following a 12-week feeding period, animals were anesthetized and mechanically ventilated. Muscle endurance (fatigue) and contractile properties were evaluated using an in situ preparation of the tibialis anterior (TA) muscle. Contractile properties of the TA muscle were determined before and after a fatigue protocol. The muscle fatigue protocol consisted of 60 min of repetitive contractions (250 ms trains at 15 Hz; duty cycle=11%) of the TA muscle. Prior to the fatigue protocol, no significant differences existed in the force-frequency curves between EDEF and CON animals. At the completion of the fatigue protocol, muscular force production was significantly ( P<0.05) lower in the EDEF group (reduced by 69%) compared to CON group (reduced by 38%). Following the fatigue protocol, a right shift existed in the force-frequency curve at low stimulation frequencies (</=40 Hz) in the EDEF animals compared to the CON animals ( P<0.05). The stimulated and the contralateral TA muscle from the EDEF animals had significantly higher markers of lipid peroxidation compared to the same muscles in the CON animals ( P<0.05). These data support the hypothesis that VE deficiency impairs muscular endurance and alters muscle contractile properties following a prolonged series of contractions.

Animals↗

PubMed2002

Dose effects of oral bovine colostrum on physical work capacity in cyclists.

PURPOSE: There is interest in the potential long-term use of dietary supplementation with bovine colostrum to enhance exercise performance. The purpose of the present study was to determine the dose effects of bovine colostrum on cycling performance. METHODS: Forty-two competitive cyclists were randomly divided into three groups and required to consume either 20 g/d bovine colostrum + 40 g whey protein concentrate (wpc), 60 g of bovine colostrum, or 60 g of wpc (placebo). Two measures were used to assess performance before (pre-) and after (post-) an 8-wk supplementation period. The first measure required subjects to complete two VO2max tests separated by 20 min with the amount of work completed in the second test used to evaluate performance. The second performance measure was the time to complete a work-based time trial following a 2-h cycle at 65% VO2max. Subjects were required to maintain their regular training and keep a food and training diary over the study period. RESULTS: After supplementation, the performance enhancement in Measure One was not statistically significantly different in the colostrum groups compared to the placebo group (placebo = 3.4%, 20 g = 4.0%, 60 g = 3.9%; 95% confidence interval (CI) for differences, +/-1.8%, P > 0.05). In performance Measure Two subjects in the 20 g and 60 g groups completed the time trial significantly (P < 0.05) faster post supplement compared to pre supplement (improvements in performance times, placebo = 37 s, 20 g = 158 s, 60 g = 134 s; 95% CI for differences, 47 s). CONCLUSION: Oral bovine colostrum supplementation at 20 g or 60 g/d provided a small but significant improvement in time trial performance in cyclists after a 2-h ride at 65% VO2max.

Administration, Oral↗

PubMed2002

Interval training program optimization in highly trained endurance cyclists.

PURPOSE: The purpose of this study was to examine the influence of three different high-intensity interval training (HIT) regimens on endurance performance in highly trained endurance athletes. METHODS: Before, and after 2 and 4 wk of training, 38 cyclists and triathletes (mean +/- SD; age = 25 +/- 6 yr; mass = 75 +/- 7 kg; VO(2peak) = 64.5 +/- 5.2 mL x kg(-1) min(-1)) performed: 1) a progressive cycle test to measure peak oxygen consumption (VO(2peak)) and peak aerobic power output (PPO), 2) a time to exhaustion test (T(max)) at their VO(2peak) power output (P(max)), as well as 3) a 40-km time-trial (TT(40)). Subjects were matched and assigned to one of four training groups (G(2), N = 8, 8 x 60% T(max) at P(max), 1:2 work:recovery ratio; G(2), N = 9, 8 x 60% T(max) at P(max), recovery at 65% HR(max); G(3), N = 10, 12 x 30 s at 175% PPO, 4.5-min recovery; G(CON), N = 11). In addition to G(1), G(2), and G(3) performing HIT twice per week, all athletes maintained their regular low-intensity training throughout the experimental period. RESULTS: All HIT groups improved TT(40) performance (+4.4 to +5.8%) and PPO (+3.0 to +6.2%) significantly more than G(CON) (-0.9 to +1.1%; P < 0.05). Furthermore, G(1) (+5.4%) and G(2) (+8.1%) improved their VO(2peak) significantly more than G(CON) (+1.0%; P < 0.05). CONCLUSION: The present study has shown that when HIT incorporates P(max) as the interval intensity and 60% of T(max) as the interval duration, already highly trained cyclists can significantly improve their 40-km time trial performance. Moreover, the present data confirm prior research, in that repeated supramaximal HIT can significantly improve 40-km time trial performance.

Adult↗

PubMed2002

Mechanical ventilation results in progressive contractile dysfunction in the diaphragm.

These experiments tested the hypothesis that a relatively short duration of controlled mechanical ventilation (MV) will impair diaphragmatic maximal specific force generation (specific P(o)) and that this force deficit will be exacerbated with increased time on the ventilator. To test this postulate, adult Sprague-Dawley rats were randomly divided into one of six experimental groups: 1) control (n = 12); 2) 12 h of MV (n = 4); 3) 18 h of MV (n = 4); 4) 18 h of anesthesia and spontaneous breathing (n = 4); 5) 24 h of MV (n = 7); and 6) 24 h of anesthesia and spontaneous breathing (n = 4). MV animals were anesthetized, tracheostomized, and ventilated with room air. Animals in the control group were acutely anesthetized but were not exposed to MV. Animals in two spontaneous breathing groups were anesthetized and breathed spontaneously for either 18 or 24 h. No differences (P > 0.05) existed in diaphragmatic specific P(o) between control and the two spontaneous breathing groups. In contrast, compared with control, all durations of MV resulted in a reduction (P < 0.05) in diaphragmatic specific tension at stimulation frequencies ranging from 15 to 160 Hz. Furthermore, the MV-induced decrease in diaphragmatic specific P(o) was time dependent, with specific P(o) being approximately 18 and approximately 46% lower (P < 0.05) in animals mechanically ventilated for 12 and 24 h, respectively. These data support the hypothesis that relatively short-term MV impairs diaphragmatic contractile function and that the magnitude of MV-induced force deficit increases with time on the ventilator.

Animals↗

PubMedDate not supplied

Exposure to automotive pollution increases plasma susceptibility to oxidation.

Low-density lipoprotein oxidation is implicated in the development of atherosclerosis. Plasma susceptibility to oxidation may be used as a marker of low-density lipoprotein oxidation and thus predict atherosclerotic risk. In this study the authors investigated the relationship between plasma susceptibility to oxidation and exposure to automotive pollution in a group of automobile mechanics (n = 16) exposed to high levels of automotive pollution, vs. matched controls (n = 13). The authors induced plasma oxidation by a free radical initiator and they determined susceptibility to oxidation by (1) change in absorbance at 234 nm, (2) lag time to conjugated diene formation, and (3) linear slope of the oxidation curve. Mechanics had significantly higher values (mean +/- standard error) for change in absorbance (1.60 +/- 0.05 vs. 1.36 +/- 0.05; p < .002), and slope (1.6 x 10(-3) +/- 0.1 x 10(-3) vs. 1.3 x 10(-3) +/- 0.1 x 10(-3); p < .001), compared with controls. These results indicate that regular exposure to automotive pollutants increases plasma susceptibility to oxidation and may, in the long-term, increase the risk of developing atherosclerosis.

Adolescent↗