Biomedical subjects

Myra A Nimmo

Publications and source records attributed to Myra A Nimmo.

10 recordsLinked to original sources

PubMed2006

Human resting extracellular heat shock protein 72 concentration decreases during the initial adaptation to exercise in a hot, humid environment.

Heat shock protein (Hsp) 72 is a cytosolic protein that also is present in the circulation. Extracellular Hsp72 (eHsp72) is inducible by exercise and is suggested to act as a danger signal to the immune system. The adaptive response of eHsp72 to repeated exercise-heat exposures in humans remains to be determined. An intracellular animal study found a reduced Hsp72 response, with no change in resting levels, during heat stress after a single day of passive heat acclimation. The current study therefore tested whether adaptations in human eHsp72 levels would similarly occur 24 hours after a single exercise-heat exposure. Seven males completed cycle exercise (42.5% V(O2peak) for 2 hours) in a hot, humid environment (38 degrees C, 60% relative humidity) on each of 2 consecutive days. Blood samples were obtained from an antecubital vein before exercise and 0 hours and 22 hours postexercise for the analysis of eHsp72. Exercise-heat stress resulted in enhanced eHsp72, with a similar absolute increase found on both days (day 1: 1.26 ng/mL [0.80 ng/mL]; day 2: 1.29 ng/mL [1.60 ng/mL]). Resting eHsp72 decreased from rest on day 1 to day 2's 22-hour postexercise sample (P < 0.05). It is suggested that the reduction in resting eHsp72 after 2 consecutive exercise-heat exposures is possibly due to an enhanced removal from the circulation, for either immunoregulatory functions, or for improved cellular stress tolerance in this initial, most stressful period of acclimation.

Adaptation, Physiological↗

PubMed2005

Skeletal muscle ATP turnover and muscle fiber conduction velocity are elevated at higher muscle temperatures during maximal power output development in humans.

The effect of temperature on skeletal muscle ATP turnover and muscle fiber conduction velocity (MFCV) was studied during maximal power output development in humans. Eight male subjects performed a 6-s maximal sprint on a mechanically braked cycle ergometer under conditions of normal (N) and elevated muscle temperature (ET). Muscle temperature was passively elevated through the combination of hot water immersion and electric blankets. Anaerobic ATP turnover was calculated from analysis of muscle biopsies obtained before and immediately after exercise. MFCV was measured during exercise using surface electromyography. Preexercise muscle temperature was 34.2 degrees C (SD 0.6) in N and 37.5 degrees C (SD 0.6) in ET. During ET, the rate of ATP turnover for phosphocreatine utilization [temperature coefficient (Q10) = 3.8], glycolysis (Q10 = 1.7), and total anaerobic ATP turnover [Q10 = 2.7; 10.8 (SD 1.9) vs. 14.6 mmol x kg(-1) (dry mass) x s(-1) (SD 2.3)] were greater than during N (P < 0.05). MFCV was also greater in ET than in N [3.79 (SD 0.47) to 5.55 m/s (SD 0.72)]. Maximal power output (Q10 = 2.2) and pedal rate (Q10 = 1.6) were greater in ET compared with N (P < 0.05). The Q10 of maximal and mean power were correlated (P < 0.05; R = 0.82 and 0.85, respectively) with the percentage of myosin heavy chain type IIA. The greater power output obtained with passive heating was achieved through an elevated rate of anaerobic ATP turnover and MFCV, possibly due to a greater effect of temperature on power production of fibers, with a predominance of myosin heavy chain IIA at the contraction frequencies reached.

Adenosine Triphosphate↗

PubMed2005

Temperature dependence of soleus H-reflex and M wave in young and older women.

The purpose of this study was to investigate the effect of altered local temperature on soleus H-reflex and compound muscle action potential (M wave) in young and older women. H-reflex and M wave responses were elicited in 10 young (22.3 +/- 3.3 years) and 10 older (72.5 +/- 3.2 years) women at three muscle temperatures: control (34.2 +/- 0.3 degrees C), cold (31.3+/-0.5 degrees C) and warm (37.1 +/- 0.2 degrees C). H-reflex output, expressed as the ratio between maximal H-reflex and maximal M wave (H(max)/M(max)), was lower in the older, compared with the younger, group, regardless of temperature. In control temperature conditions, for example, the H(max)/M(max) ratio was 36.8 +/- 24% in the young and 25.4 +/- 20% in the older (P<0.05). Warming had no effect on the H-reflex output in either group, whilst cooling increased H-reflex output only in the younger group (+28%). In both groups, cooling increased (+5.3%), and warming decreased (-5.5%) the H-reflex latency. This study confirms that older individuals experience a reduced ability to modulate the reflex output in response to a perturbation. In a cold environment, for example, the lack of facilitation in the reflex output, along with a delayed reflex response could be critical to an older individual in responding to postural perturbations thus potentially compromising both static and dynamic balance.

Action Potentials↗

PubMed2004

The reproducibility of closed-pouch sweat collection and thermoregulatory responses to exercise-heat stress.

Seven active male subjects cycled for 60 min at 29.5 (0.8)% peak work rate on three separate occasions in a hot environmental condition [36.0 (0.1) degrees C, 60 (1)% relative humidity] in order to determine the reproducibility of a closed-pouch sweat collection technique for sweat composition at the scapula, forearm and thigh. To confirm that sweat composition was not influenced by between-trial variations in sudomotor drive, local sweat rate, whole-body sweat rate, heart rate (HR), rectal temperature (T(re)) and mean skin temperature (T(sk)) responses were also measured, consequently reproducibility was also established for these variables. Sweat composition did not differ among trials, with the mean coefficients of variation (CVs) for sweat [Na(+)], [K(+)] and pH being 10.4 (7.4)%, 8.1 (6.5)% and 1.3 (1.1)%, respectively. Local sweat rates did not differ among the three trials (P>0.05) although whole-body sweat rate was reduced in the third trial (P<0.05). The mean CVs were 11.0 (7.8)% and 4.7 (1.6)% for local and whole-body sweat rates, respectively. Between-trial differences were not evident for T(re), T(sk) or HR with mean CVs of 0.3 (0.2)%, 0.7 (0.6)% and 3.9 (1.7)%, respectively, although HR tended to be greater in the first trial ( P=0.08). It is proposed that moderate variations in sweat composition were influenced by variations in the local sweat rate, which were induced by application of the pouch.

Adult↗

PubMed2004

During exercise in the cold increased availability of plasma nonesterified fatty acids does not affect the pattern of substrate oxidation.

Exercise in the cold was investigated to establish if the relative contribution of fat to energy expenditure is affected by the increased availability of circulating nonesterified fatty acids (NEFA). Seven men after an overnight fast cycled at approximately 70% of peak oxygen uptake for 60 minutes at an ambient temperature of 0.0 degrees C +/- 0.1 degrees C. Fifteen minutes prior to exercise and then throughout the exercise, subjects were infused with either heparin (heparin) or saline (control). Immediately before exercise NEFA concentration (control, 0.27 +/- 0.04 mmol. L(-1); heparin 1.09 +/- 0.13 mmol. l(-1)) was significantly higher (P <.05) in the heparin trial. Pre-exercise concentration of plasma triacylglycerol (TG), blood glycerol, glucose, oxygen consumption (VO(2)) and respiratory exchange ratio (RER) were not significantly different between heparin and control trials. During exercise, plasma NEFA and blood glycerol concentrations were significantly higher (P <.05) in the heparin trial, and levels of plasma TG and glucose were not different between trials. Over the exercise period rectal temperature, mean skin temperature, VO(2), RER, and heart rate (HR) were not different between the 2 trials. Gross energy expenditure of cycling (control, 3.3 +/- 0.1 MJ; heparin 3.3 +/- 0.1 MJ), the oxidation rates of fat (control, 0.67 +/- 0.05 g. min(-1); heparin, 0.71 +/- 0.06 g. min(-1)) and carbohydrate (CHO) (control, 1.68 +/- 0.04 g.min(-1); heparin, 1.62 +/- 0.17 g. min(-1)) and the proportion of energy derived from fat (control, 43 +/- 4%; heparin trial, 44 +/- 9%) and CHO (control, 57 +/- 4%; heparin trial, 56 +/- 4%) were not different between the 2 trials. These findings suggest that despite increased availability of plasma NEFA, the pattern of substrate oxidation during exercise in cold temperatures does not change. This implies that uncoupling between the availability and oxidation of plasma NEFA may be a mechanism involved in the reduced oxidation of fat seen during cold exposure. Further research is needed on the utilization of intramuscular TG and circulating plasma TG-rich lipoproteins in the cold.

Adult↗

PubMed2004

Fat oxidation after acipimox-induced reduction in plasma nonesterified fatty acids during exercise at 0 degrees C and 20 degrees C.

The main aim of this study was to investigate if whole body fat oxidation, after acipimox administration, during submaximal exercise in the cold, is different from that at temperate environments. Seven healthy recreationally active male subjects cycled at 70% Vo(2peak) for 60 minutes; once at 0 degrees C and once at 20 degrees C. To exclude availability, and therefore oxidation of plasma-derived nonesterified fatty acids (NEFA), 90 minutes before each cycling bout, subjects ingested 250 mg of the antilipolytic drug, acipimox. Blood and expired gas measurements were obtained at rest, immediately before exercise, and at 15, 30, 45, and 60 minutes of exercise. In both trials, after the ingestion of acipimox, plasma NEFA concentrations fell dramatically and immediately before and during exercise were lower than 0.05 mmol. L(-1) in both trials. Pre-exercise and exercise values of glycerol, glucose, triacylglycerol (TG), and rectal temperature (T(re)) were not different between the 0 degrees C and 20 degrees C trials. During exercise at 0 degrees C, skin temperature (T(sk)) was significantly reduced from pre-exercise values (P <.05) and at all time points was significantly lower than during exercise at 20 degrees C. Muscle temperature did not differ between trials but in both trials was lower (P <.05) at 1 cm depth than at 3 cm and 2 cm. Gross energy expenditure of cycling (0 degrees C trial, 3.6 +/- 0.1 MJ; 20 degrees C trial, 3.6 +/- 0.1 MJ), the oxidation rates of carbohydrate (0 degrees C, 32.4 +/- 0.5 KJ. min(-1); 20 degrees C, 32.6 +/- 0.7 KJ. min(-1)) and fat (0 degrees C, 24.6 +/- 1.2 KJ. min(-1); 20 degrees C, 23.0 +/- 1.8 KJ. min(-1)), and the proportion of energy derived from fat (0 degrees C, 45 +/- 1 %; 20 degrees C, 40 +/- 4%) and carbohydrate (0 degrees C, 55 +/- 1%; 20 degrees C, 58 +/- 3%) were not different between the 2 trials. In conclusion, after acipimox administration, whole body fat oxidation during exercise, designed to avoid adjustment of core temperature or thermogenesis, is not different at 0 degrees C compared with 20 degrees C. This allows the inference that during submaximal exercise, cold has no effect on the utilization of intramuscular TG (IMTG).

Adult↗

PubMed2002

Contractile muscle volume and agonist-antagonist coactivation account for differences in torque between young and older women.

It is controversial whether specific tension (the ratio between muscle strength and size) declines with aging. Therefore, contractile muscle volume was estimated separately from the intramuscular noncontractile tissue by magnetic resonance imaging, and maximum isometric torque was measured in the knee extensors and flexors of 10 young (22.8 +/- 5.7 years) and 10 older (69.5 +/- 2.4 years) healthy active women. Specific tension was lower in the older women both in the extensors (93.1 +/- 20.1 kN x m(-2) vs. 112.1 +/- 12.3 kN x m(-2); P < 0.05) and in the flexors (100 +/- 31 kN x m(-2) vs. 142.7 +/- 23.9 kN x m(-2); P < 0.01). This was accompanied by an increase in the percentage coactivation of the knee flexors during knee extension. These data suggest that the lower level of muscle torque in the older women can be explained not only by smaller contractile muscle mass but also by increased coactivation of the antagonist muscles during knee extension.

Adult↗

PubMed2002

Effects of reduced ambient temperature on fat utilization during submaximal exercise.

PURPOSE: The influence of cold air exposure on fuel utilization during prolonged cycle exercise was investigated. METHODS: Nine male subjects cycled for 90 min in ambient temperatures of -10 degrees C, 0 degrees C, 10 degrees C, and 20 degrees C. External work performed between conditions was constant. Mean oxygen consumption (VO2) over the 90 min in the 20 degrees C trial corresponded to 64 +/- 5.8% VO2peak. RESULTS: Although mean skin temperature was different between trials (P < 0.05), rectal temperatures were not different. At -10 degrees C and 0 degrees C, the respiratory exchange ratio was higher compared with 10 degrees C and 20 degrees C (0.98 +/- 0.01 and 0.97 +/- 0.01 vs 0.92 +/- 0.01 and 0.91 +/- 0.01; P < 0.05). The associated rates of fat oxidation were lower at -10 degrees C and 0 degrees C compared with 10 degrees C and 20 degrees C (0.15 +/- 0.06 and 0.17 +/- 0.06 vs 0.35 +/- 0.06 and 0.40 +/- 0.04 g.min-1; P < 0.05). Blood glycerol was lower at -10 degrees C and 0 degrees C compared with 20 degrees C (P < 0.05); mean values were 0.13 +/- 0.0, 0.13 +/- 0.0, and 0.18 +/- 0.0 mmol.L-1 for the -10 degrees C, 0 degrees C, and 20 degrees C trials, respectively. Mean VO2 was lower in the -10 degrees C trial than the 20 degrees C trial (2.53 +/- 0.06 vs 2.77 +/- 0.09. L.min-1; P < 0.05). Mean blood glucose concentrations were lower at -10 degrees C than 20 degrees C (4.9 +/- 0.2 vs 5.3 +/- 0.1 mmol.L-1; P < 0.05). Although plasma epinephrine concentrations were greater during the 20 degrees C trial compared with all other trials (P < 0.05), plasma norepinephrine did not differ between trials. CONCLUSION: The diminished fat oxidation at colder temperatures potentially reflects a reduction in lipolysis and/or mobilization of FFA or impairment in the oxidative capacity of the muscle.

Adipose Tissue↗

PubMed2002

Muscle function in elite master weightlifters.

PURPOSE: To determine whether explosive power and isometric strength of the lower-limb muscles in elite master Olympic weightlifters declines at a similar rate to nontrained healthy controls with increasing age. METHODS: 54 elite level masters weightlifters (aged 40-87), who were competitors at the World Masters Weightlifting Championships (1999), were compared with a similar number of aged-matched, healthy untrained individuals. Isometric knee extensor strength and lower-limb explosive power were tested. Extent of antagonist co-contraction during isometric knee extension was determined by EMG and power loading characteristics by using a variable inertial system. Muscle volume was estimated using anthropometry. RESULTS: On average, the weightlifters were able to generate 32% more peak power (P < 0.05) in the lower limbs and 32% more isometric knee extensor force (P < 0.05) than the control subjects. No significant differences in lower-leg volume were observed between the two groups. Peak power declined at a similar rate with increasing age in the weightlifters and controls (1.2 and 1.3% of a 45-yr-old's value per year), as did strength, but at a lower rate (0.6 and 0.5% per year). The inertial load at which the weightlifters achieved their maximal peak power output was greater (P < 0.05) than the controls. The torque generated at this optimal inertia was also greater in the weightlifters (P < 0.05), whereas the time taken for the weightlifters to reach their maximal peak power was on average 13% shorter (P < 0.05). No differences in antagonist co-contraction during isometric knee extension were observed between the two groups. CONCLUSIONS: Muscle power and isometric strength decline at a similar rate with increasing age in elite master weightlifters and healthy controls. In spite of inertial load optimization, muscle power declined in both groups at approximately twice the rate of isometric strength. Although similar rates of decline were observed, the absolute differences between the weightlifters and controls were such that an 85-yr-old weightlifter was as powerful as a 65-yr-old control subject. This would therefore represent an apparent age advantage of approximately 20 yr for the weightlifters.

Adult↗

PubMed2002

Effect of active warm-up on metabolism prior to and during intense dynamic exercise.

PURPOSE: This study investigated whether active warm-up (AW) would increase muscle acetylcarnitine concentration before exercise, thereby reducing the reliance on nonoxidative ATP production during subsequent high-intensity exercise. METHODS: Six female subjects performed a 30-s sprint at 120% of their maximal power output on an electronically braked cycle ergometer 5 min after undertaking an active warm-up. To exclude any effect of muscle temperature (Tm) on metabolism, AW was compared with control (C), which involved passively heating the muscle to the same temperature as that achieved by active warm-up (37.1 +/- 0.3 vs 37.2 +/- 0.2 degrees C AW and C, respectively). RESULTS: Active warm-up significantly increased the concentration of acetylcarnitine from 4.5 +/- 1.5 mmol x kg(-1) dry muscle (dm)(-1) at rest to 9.4 +/- 1.6 mmol x kg dm(-1) before the onset of exercise. There was no change in acetylcarnitine concentration in C. During exercise the accumulation of muscle lactate was significantly less in AW compared with C (21.9 +/- 3.8 vs 34.3 +/- 2.3 mmol.kg dm, respectively). CONCLUSION: The main finding of this study was that there was less accumulation of blood and muscle lactate during intense dynamic exercise preceded by active warm-up, which could not be accounted for by a difference in T between trials immediately before the onset of exercise(m)

Acetylcarnitine↗