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Biomedical subjects

Mary Nevill

Publications and source records attributed to Mary Nevill.

6 recordsLinked to original sources
PubMed2005

Age is an important determinant of the growth hormone response to sprint exercise in non-obese young men.

BACKGROUND: The factors that regulate the growth hormone (GH) response to physiological stimuli, such as exercise, are not fully understood. The aim of the present study is to determine whether age, body composition, measures of sprint performance or the metabolic response to a sprint are predictors of the GH response to sprint exercise in non-obese young men. METHODS: Twenty-seven healthy, non-obese males aged 18-32 years performed an all-out 30-second sprint on a cycle ergometer. Univariate linear regression analysis was employed to evaluate age-, BMI-, performance- and metabolic-dependent changes from pre-exercise to peak GH and integrated GH for 60 min after the sprint. RESULTS: GH was elevated following the sprint (change in GH: 17.0 +/- 14.2 microg l(-1); integrated GH: 662 +/- 582 min microg l(-1)). Performance characteristics, the metabolic response to exercise and BMI were not significant predictors of the GH response to exercise. However, age emerged as a significant predictor of both integrated GH (beta = -0.547, p = 0.003) and change in GH (beta = -0.448, p = 0.019) after the sprint. CONCLUSION: In non-obese young men, age is a more important predictor of GH following sprint exercise than BMI, sprint performance or the metabolic response to sprint exercise.

Adolescent↗
PubMed2005

Human growth hormone responses to repeated bouts of sprint exercise with different recovery periods between bouts.

This study examined the growth hormone (GH) response to repeated bouts of sprint cycling. Eight healthy men completed three trials consisting of two 30-s sprints on a cycle ergometer separated by either 60 min (Trial A) or 240 min (Trial B) of recovery and a single 30-s sprint carried out the day after Trial B (Trial C). Trials A and B were separated by at least 7 days. Blood samples were obtained at rest and during recovery from each sprint. In Trial A, GH was elevated immediately before sprint 2, and there was no further increase in GH following the second sprint [area under the curve: 460 (SD 348) vs. 226 min.mug(-1).l(-1) (SD 182), P = 0.05]. Free insulin-like growth factor I tended to be lower immediately before sprint 2 than sprint 1 (P = 0.06). Serum free fatty acids were not different immediately before each of the sprints. In Trial B, there was a trend for a smaller GH response to the second sprint [GH area under the curve: 512 (SD 396) vs. 242 min.mug(-1).l(-1) (SD 190), P = 0.09]. Free insulin-like growth factor I tended to be lower (P = 0.06), and serum free fatty acids were higher (P = 0.01) immediately before sprint 2 than sprint 1. There was no difference in the GH response to sprinting on consecutive days (Trials B and C). In conclusion, repeated bouts of sprint cycling on the same day result in an attenuation or even ablation of the exercise-induced increase in GH, depending on the recovery interval between sprints.

Acceleration↗
PubMed2002

Effect of the menstrual cycle on performance of intermittent, high-intensity shuttle running in a hot environment.

The present study examined the impact of the menstrual cycle and oral contraceptive use on performance of high-intensity intermittent running in the heat [31.0 (0.2) degrees C; 23.1 (0.9)% relative humidity]. Seven normally menstruating women (NM) and eight oral contraceptive (OC) users participated in the study. Two trials were undertaken near the predicted mid-point of the follicular (FT) and luteal (LT) phases of the menstrual cycle and the equivalent days for the OC users. Basal serum progesterone concentrations were higher during the LT for the NM group [FT: 2.42 (0.28) nmol l(-1) vs LT: 25.96 (11.28) nmol l(-1); P<0.05], but were not different for the OC users [days 1-14: 2.79 (0.38) nmol l(-1) vs days 15-28: 2.61 (0.32) nmol l(-1)]. There were no differences in distance run between menstrual cycle phases or between the normally menstruating and OC groups [NM FT: 6257 (1401) m vs LT: 5861 (1035) m]. However, the OC ran further in days 15-28 compared to days 1-14 [OC 1-14: 5481 (612) m vs 15-28: 6615 (893) m, P<0.05]. For the NM, rectal temperature, perceived exertion, estimated SR, serum growth hormone, plasma lactate, ammonia and glucose did not differ between phases of the menstrual cycle. For the OC group, heart rate, perceived exertion, sweat rate, plasma lactate and ammonia did not differ between days 1-14 of OC use and days 15-28. However, rectal temperature was higher ( P<0.05) and growth hormone tended to be higher ( P=0.05) during days 15-28, while plasma glucose was lower ( P<0.05). These results demonstrate that for unacclimatised games players the performance of intermittent, high-intensity shuttle running in the heat is unaffected by menstrual cycle phase but is influenced by OC use.

Adult↗
PubMed2002

Absorption of creatine supplied as a drink, in meat or in solid form.

We examined the plasma concentration curve obtained over 6 h after the ingestion of 2 g of creatine (Cr) (equivalent to 2.3 g Cr x H2O) contained in meat or in solution in five non-users of creatine supplements. Peak plasma creatine concentration was lower after the ingestion of meat but was maintained close to this for a longer period. Measurements of the area under the plasma concentration curve indicated approximate bioequivalence of creatine contained in meat with the same dose supplied in a solution. In a separate study, we examined the plasma concentration time curve after ingestion of solid Cr x H2O. Creatine ingested as a lozenge (crushed in the mouth and swallowed) or as a crystalline suspension in ice cold water resulted in a 20% lower peak concentration and 30-35% smaller area under the plasma creatine concentration curve than the same dose administered in solution. Despite a possibly lower bioavailability, 2.3 g Cr x H2O supplied in either solid form was nonetheless sufficient to raise the plasma concentration five- to six-fold in individuals with a mean body mass of 75.6 kg. We conclude that creatine administered as meat or in solid form is readily absorbed but may result in slightly lower peak concentrations than when the same dose is ingested as a solution.

Adult↗