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Biomedical subjects

D G Jenkins

Publications and source records attributed to D G Jenkins.

16 recordsLinked to original sources
PubMed1994

The physiological and ventilatory responses to repeated 60 s sprints following sodium citrate ingestion.

This study examined the influence of sodium citrate on changes in selected blood, ventilatory and performance variables in response to intermittent sprint exercise. Eight moderately active male students completed three tests over a 6 day experimental period. The first test involved incremental exercise to determine VO2 max, while the second and third tests were identical in nature and involved five 60 s sprints cycling against 0.075 kg kg-1 body mass (BM); each of the five sprints was separated by 5 min passive seated recovery. Three days separated the VO2 max test and first interval test, while a further 3 days elapsed between the first and second interval tests. Ninety minutes prior to each interval test, the subjects consumed either a solution of sodium citrate (0.5 g kg-1 BM) or a placebo solution (1 g of calcium carbonate and 4 mg of sodium chloride). These were randomly administered in a double-blind crossover procedure so that every subject consumed each solution prior to the interval test over the 6 day period. Measures of work, VE, VO2, VCO2, post-exercise plasma lactate, and changes in both venous blood pH and venous blood bicarbonate (HCO3-) were measured during each interval test. Although analysis of variance failed to identify differences in performance between the two solutions, both exercise VCO2 and changes in venous blood HCO3- were higher in the citrate condition (P < 0.05). In addition, both peak post-exercise plasma lactate concentrations and post-exercise venous blood pH were significantly higher following citrate ingestion. Although these data are consistent with greater clearance of lactate and H+ from the active muscle cells following citrate ingestion, performance between the two trials was the same.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Endurance training enhances critical power.

The present investigation was conducted to determine whether critical power (CP) assesses the ability to perform continuous aerobic exercise and to determine whether training-induced changes in aerobic endurance are reflected by changes in the slope, but not the y-intercept of the CP function. Twelve healthy, active, but untrained male students (mean age +/- SD = 19.1 +/- 0.8 yr) undertook 8 wk of cycle ergometer endurance training (30-40 min a day, three times a week) at an intensity corresponding to their CP. Six control subjects of similar age and initial training status refrained from regular exercise for the same period. Before and immediately following the training period, each of the 18 participants completed three cycle ergometer tests to determine their CP function, an incremental exercise task to establish their maximal oxygen uptake (VO2max), and 40 min of continuous cycle ergometry at or near their calculated CP. CP was significantly correlated with endurance time at 270 W (r = 0.65, P < 0.05) and with the mean power that could be maintained for 40 min (r = 0.87-0.95, P < 0.01), but overestimated the latter by less than 6%. In response to endurance training, CP increased from a mean of 196 +/- 40.9 W to 255 +/- 28.4 W (31%) (ANCOVA, P < 0.01), while the mean power output maintained for 40 min of exercise increased from 190 +/- 34.5 W to 242 +/- 34.9 W (28%). VO2max increased from 49.2 +/- 7.8 ml.kg-1.min-1 to 53.4 +/- 6.4 ml.kg-1.min-1 (8.5%) (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

The y-intercept of the critical power function as a measure of anaerobic work capacity.

When bouts of muscular work are performed to exhaustion at different intensities, the slope of the regression of maximal work (work limit) on maximal time (time limit) is referred to as critical power (CP). The y-intercept of this function is considered to represent anaerobic work capacity (AWC). The purpose of this investigation was to examine the relationship between the y-intercept from the critical power curve and measures of AWC (total work accomplished, maximal blood lactate and post-exercise venous blood pH) gained from repeated, maximal exercise. Nine male volunteers of moderately high training status (VO2 max 4.45 +/- 0.251/min) completed three cycle ergometer tests to exhaustion (at 300, 350 and 400 W) for the determination of CP. A second cycle ergometer task involved repeated maximal effort (against 0.075 N/kg body mass) over five 1 min periods. Five min of passive recovery separated each exercise bout, at the end of which capillary blood was collected for lactate analysis. On completion of the fifth bout, venous blood was sampled for the determination of blood pH. Total accumulated work provided a performance estimate of AWC which, together with blood lactate and pH, was compared to the y-intercept. Correlation analysis revealed a significant relation between the y-intercept and total work accomplished (r = 0.74; p less than 0.05), while post-exercise venous blood pH was positively related to both the y-intercept (r = 0.92; p less than 0.01) and the accumulated work recorded (r = 0.92; p less than 0.01). No significant correlation between peak blood lactate and work was found (r = 0.16; ns), although a relation between post-exercise venous blood pH and VO2 max was established (r = 0.84; p less than 0.05). The capacity for high intensity interval work was well represented by the y-intercept in active males. Furthermore, the relations between blood pH and both the y-intercept and accumulated work suggest that either improved buffering or a greater contribution of aerobic metabolism to the energy yield may have been responsible for the more successful performances in the interval exercise.

Acid-Base Equilibrium↗
PubMed1990

Blood lactate in trained cyclists during cycle ergometry at critical power.

The purposes of this investigation were to determine the validity of critical power (CP) as a measure of the work rate that can be maintained for a very long time without fatigue and to determine whether this corresponded with the maximal lactate steady-state (lass,max). Eight highly trained endurance cyclists (maximal oxygen uptake 74.1 ml.kg-1.min-1, SD 5.3) completed four cycle ergometer tests to exhaustion at pre-determined work rates (360, 425, 480 and 520 W). From these four co-ordinates of work and time to fatigue the regression of work limit on time limit was calculated for each individual (CP). The cyclists were then asked to exercise at their CP for 30 min. If CP could not be maintained, the resistance was reduced minimally to allow the subject to complete the test and maintain a blood lactate plateau. Capillary blood was sampled at 0,5,10,20 and 30 min into exercise for the analysis of lactate. Six of the eight cyclists were unable to maintain CP for 30 min without fatigue. In these subjects, the mean power attained was 6.4% below that estimated by CP. Mean blood lactates (n = 8) reached a steady-state (8.9 mmol.l-1 SD 1.6) during the last 20 min of exercise indicating that CP slightly overestimated lass,max, Individual blood lactates during the last 20 min of exercise were more closely related to the gamma-intercept of the CP curve (r = 0.78, P less than 0.05) than either CP (0.34, NS) or mean power output (r = 0.42, NS).

Adolescent↗
PubMed1976

Tofranil in the treatment of low back pain.

This report describes a double-blind between-group comparison of Tofranil and placebo in fifty-nine patients admitted to the Joint Service Medical Rehabilitation Unit suffering from low back pain. Patients were given 25 mg of either Tofranil or placebo three times a day for four weeks. Fifteen patients were not included in the analysis, nine dropping out for non-trial related reasons, two dropping out complaining of lost libido and four not taking the tablets, or taking additional drugs. One of the patients complaining of lost libido was taking Tofranil and the other was taking placebo. Over the whole sample there was no significant benefit for Tofranil over placebo as regards physical measurements. Both Tofranil and placebo groups showed a significant improvement during the trial on straight leg raise and backward flexion. For lateral flexion the Tofranil group was significantly worse than the placebo group on entering the trial, and during the trial the Tofranil group improved to match the placebo group. The clinician's pain and stiffness assessments and the patients' pain and stiffness assessments show a significant improvement for both the Tofranil and placebo groups during the trial. However, no difference is shown between Tofranil and placebo. The psychological tests show no difference between Tofranil and placebo and only a marinal improvenmet over initial condition. Further analysis according to initial diagnosis showed nothing conclusive. Numerically, the use of Tofranil produced a marked improvement in pain and stiffness in patients with 'disc lesion only' diagnoses, whereas placebo did not produce an improvement. However, this observation was far from reaching statistical significance. Side-effects were not severe for either drug. Additional medication was rarely used.

Adolescent↗