Healthy Young Male Subjects Research Articles

Hypertrophy with unilateral resistance exercise occurs without increases in endogenous anabolic hormone concentration

We aimed to gain insight into the role that the transitory increases in anabolic hormones play in muscle hypertrophy with unilateral resistance training. Ten healthy young male subjects (21.8 +/- 0.4 years, 1.78 +/- 0.04 m, 75.6 +/- 2.9 kg; mean +/- SE) engaged in unilateral resistance training for 8 week (3 days/week). Exercises were knee extension and leg press performed at 80-90% of the subject's single repetition maximum (1RM). Blood samples were collected in the acute period before and after the first training bout and following the last training bout and analyzed for total testosterone, free-testosterone, luteinizing hormone, sex hormone binding globulin, growth hormone, cortisol, and insulin-like growth factor-1. Thigh muscle cross sectional area (CSA) and muscle fibre CSA by biopsy (vastus lateralis) were measured pre- and post-training. Acutely, no changes in systemic hormone concentrations were observed in the 90 min period following exercise and there was no influence of training on these results. Training-induced increases were observed in type IIx and IIa muscle fibre CSA of 22 +/- 3 and 13 +/- 2% (both P < 0.001). No changes were observed in fibre CSA in the untrained leg (all P > 0.5). Whole muscle CSA increased by 5.4 +/- 0.9% in the trained leg (P < 0.001) and remained unchanged in the untrained leg (P = 0.76). Isotonic 1RM increased in the trained leg for leg press and for knee extension (P < 0.001). No changes were seen in the untrained leg. In conclusion, unilateral training induced local muscle hypertrophy only in the exercised limb, which occurred in the absence of changes in systemic hormones that ostensibly play a role in muscle hypertrophy.

Finasteride 1 mg has no inhibitory effect on omeprazole metabolism in extensive and poor metabolizers for CYP2C19 in Japanese

To examine the inhibitory effect of finasteride 1 mg on the metabolism of omeprazole in genetically determined extensive (EMs) and poor metabolizers (PMs) for CYP2C19 in young healthy Japanese male subjects. Twenty-four volunteers participated in this study, among whom 12 were homozygous EMs and 12 were PMs for CYP2C19. A single center, controlled, randomized, open, crossover study with a 5 day washout between the two study periods was performed. Each of the six EMs and PMs received a single oral 20 mg dose of omeprazole on day 1 (treatment I). After a 5 day washout period, these subjects received 1 mg of finasteride once a day for three consecutive days, and a single oral 20 mg dose of omeprazole was co-administered on day 3 (treatment II). The 12 other EMs and PMs received treatments I and II in reverse. Plasma samples were collected for up to a 12 hours postdose of omeprazole, and the pharmacokinetic parameters of omeprazole were determined. The geometric mean ratio (GMR) for the AUC((0-12 hr)) of omeprazole when co-administered with finasteride/omeprazole alone is 1.13 (90%CI, 1.03, 1.25) and 0.96 (0.88, 1.05) in EMs and PMs, respectively. Finasteride did not significantly alter C(max), T(max) and t(1/2) in both genotypes. Finasteride 1 mg, widely used for the treatment of androgenetic alopecia in men, did not meaningfully increase omeprazole exposure (20 mg) in both EMs and PMs for CYP2C19. These results indicate that finasteride does not meaningfully inhibit CYP2C19 activity in vivo at the dose of 1 mg.

Safety, tolerability and pharmacokinetics of escalating doses of NXY-059 in healthy young and elderly subjects

ABSTRACTObjective: NXY-059 is a novel, free-radical trapping, neuroprotectant that reduces infarct size and preserves brain function in animal models of acute ischaemic stroke. This study evaluated the safety, tolerability and pharmacokinetics of NXY-059 in the unbound steady-state plasma concentration (Cuss) exposure range of 50-300 μmol/L in healthy young and elderly subjects.Research design and methods: The primary objective of this two-centre, randomised, double-blind, placebo-controlled, dose-escalating study was to investigate the safety and tolerability, including renal function parameters and vasoirritative effects, of 8‐h and 72‐h intravenous infusions of NXY‐059 in healthy young (20–45 years) and elderly (55–75 years) male and female subjects. The secondary objective of the study was to evaluate the pharmacokinetics of 8‐h and 72‐h intravenous infusions of NXY‐059 in these subjects, using blood and urine samples taken during and after NXY‐059 infusion as well as the doses administered.Results: Of the 104 healthy volunteers who participated in the study, 72 were young and 32 were elderly. The type and incidence of adverse events in NXY‐059 and placebo subjects were similar, although headache was more common in the NXY‐059 group. Renal function was not altered in either group. Thrombophlebitis was reported in two elderly subjects: one receiving NXY-059 and one receiving placebo. A proportional relationship between AUC and dose for the 8‐h and 72‐h infusions was observed, and clearance did not change with dose.Conclusions: NXY-059 was well tolerated at all plasma concentrations tested in both the young and elderly subjects, and no safety concerns were raised. Linear pharmacokinetics were observed following 8‐h and 72‐h infusions of NXY‐059 at doses resulting in an average Cuss in the 52–317 µmol/L range.

Distribution of wall shear rate throughout the arterial tree: A case study

The generally accepted assumption that the arterial system remodels itself to maintain constant wall shear stress throughout is based on Murray’s law, utilising the principle of minimum work for steady flow. However, blood flow in the human arterial system is pulsatile. In this work we outline a method allowing for estimation of wall shear rate in arteries using the flow waveforms as the input signal and estimate wall shear rates in the common carotid, brachial, and femoral arteries to determine the uniformity of distribution of wall shear rates throughout the arterial system. Time-dependent wall shear rates occurring in fully developed pulsatile flow were obtained using Womersley’s theory. Flow waveforms and radii of the arteries measured in a young healthy male subject without any known cardiac disease using magnetic resonance taken from the literature were used as the input to the model. Peak/mean wall shear rates were found to be (1640/403.2 s −1) in common carotid, (908.8/84.95 s −1) in brachial, and (1251/134.2 s −1) in femoral arteries. Our findings suggest a non-uniform distribution of wall shear rates throughout the arterial system. The advantage of using this method is that such input data are being routinely recorded during diagnostic ultrasonography.

Proton and sodium MRI assessment of fluid level in calf tissue

To investigate the feasibility of using (1)H and (23)Na MRI to detect fluid levels in the lower leg muscle. Proton and sodium MRI was applied to detect body fluid levels in the lower leg muscles of 18 healthy young male subjects at 3T and 4T. The paradigms under investigation were a postural change from sitting upright to lying supine, and saline infusion. We found that the average proton MR signal in gastrocnemius and soleus muscles were reduced following the postural change by 3.5% +/- 1.4% (P < 0.05) and rose following saline infusion by 3.7% +/- 0.9% (P < 0.01). More dramatically, the sodium MR signal decreased by 7.1% +/- 1.2% (P < 0.01) following the postural change and increased following saline infusion by 12% +/- 3.8% (P < 0.05). The ratio of intra- to extracellular fluid levels was 1.6 +/- 0.5 for the subjects based on the acquired proton and sodium data. Our results indicate that proton and sodium MRI can be used to assess fluid levels in the lower extremities, and this technique may be applied to evaluate fluid retention.

Substrate utilization during prolonged exercise with ingestion of 13C-glucose in acute hypobaric hypoxia (4,300 m)

Energy substrate oxidation was measured using indirect respiratory calorimetry combined with tracer technique in five healthy young male subjects, during a 80-min exercise period on ergocycle with ingestion of 140 g of (13)C-labelled glucose, in normoxia and acute hypobaric hypoxia (445 mmHg or 4,300 m), at the same relative [77% V(.-)((O)(2)(max))] and absolute workload (161+/-8 W, corresponding to 77 and 54% V(.-)((O)(2)(max)) in hypoxia and normoxia). The oxidation rate of exogenous glucose was not significantly different in the three experimental situations: 21.4+/-2.9, 20.2+/-1.2 and 17.2+/-0.6 g over the last 40 min of exercise at approximately 77 and approximately 54% V(.-)((O)(2)(max)) in normoxia and in hypoxia, respectively, providing 12.5+/-1.5, 16.8+/-1.1 and 14.9+/-1.1% of the energy yield, although ingestion of glucose during exercise resulted in a higher plasma glucose concentration in hypoxia than normoxia. The contribution of carbohydrate (CHO) oxidation to the energy yield was significantly higher in hypoxia (92.0+/-2.1%) than in normoxia for both a given absolute (75.3+/-5.2%) and relative workload (78.1+/-1.8%). This greater reliance on CHO oxidation in hypoxia was entirely due to the significantly larger contribution of endogenous glucose oxidation to the energy yield: 75.9+/-1.7% versus 66.6+/-3.3 and 55.2+/-3.7% in normoxia at the same relative and absolute workload.

Non-Invasive Determination of Hemodynamic Variables and their Relationship to the Anaerobic Threshold

Determination of non-invasive homodynamic monitoring using impedance cardiography has been shown to be possible at rest and during exercise. PURPOSE: To determine the relationship of various homodynamic variables to the anaerobic threshold during upright cycle ergometry. METHODS: Twenty-five moderately trained healthy young male subjects (mean±SD) age: 24±4 yrs; weight: 78±7 kg; height: 182±6 cm) performed an incremental cycle ergometer test in an upright position. Two submaximal markers of energy supply were denned by means of blood lactate concentration (LA): aerobic threshold (AeT): first abrupt increase of LA above resting levels; anaerobic threshold (AnT): second abrupt increase of LA between AeT and maximal workload (Pmax). Non-invasive homodynamic monitoring was performed in supine position prior to the test and during the exercise test using a combination of impedance cardiography and vascular unloading technique to measure stroke volume (SV), cardiac output (CO), systolic blood pressure (BP) and total peripheral resistance index (TPRI) (Task Force® Monitor, CNSystems, Graz, Austria). The determination of break points in all measured variables was conducted by means of computer-aided linear regression break point analysis between AeT and Pmax. RESULTS: Workload (P) and heart rate (HR) at Pmax were 331±35 W and 185±10 min−1, respectively. SV was significantly higher, BP and TPRI were significantly lower at supine compared to the upright position at rest. SV, BP, CO increased, TPRI decreased steadily from resting values to Pmax. BP showed a plateau at workload above AnT. A break point was observed in measured variables in most of the subjects. One-way ANOVA revealed no statistical significant difference (P>0.05) for workload at AnT of 242±29 W, (N=25) and at workload of the breakpoint for SV 247±41 W (N=19), CO of 249±40 W, N=18), TPRI of 232±37 W (N=22) and BP of 239±36 W (N=25). Significant correlations (P<0.001) were observed between workload at AnT and at workload of the breakpoint for SV (r=0.76), CO (r=0.80), TPRI (r=0.65) and BP (r=0.63). CONCLUSIONS: We conclude that there is a strong relationship between the AnT and multiple homodynamic variables. Non-invasive homodynamic monitoring using impedance electrocardiography and vascular unloading technique seems to be useful for application during upright cycle ergometry.

The application of surface plethysmography for heart rate variability analysis after GSM radiofrequency exposure

The aim of the present study was to test whether the electromagnetic field emitted by standard GSM mobile phones results in changes in heart rate (HR) and heart rate variability (HRV) of 35 healthy young male and female subjects. Two parallel signals, electrocardiogram and infrared surface plethysmogram were recorded and compared to test their validity for the analysis. Plethysmographic recording is proved to be a fast and reliable method for HRV measurements. In the radiofrequency (RF) exposure study, there was no significant difference in the values of HR and HRV between the RF and the sham groups. Our preliminary study demonstrates that, in our experimental conditions, RF fields emitted by cellular phones do not cause observable effects on the regulation of heart rate of healthy, young adults.

The Effects of Exercise in Forest and Urban Environments on Sympathetic Nervous Activity of Normal Young Adults

In Japan, forest-air bathing and walking (shinrin-yoku) has been proposed as a health-facilitating activity in which people spend a short period of time in a forest environment. Initially, we examined the usefulness of salivary amylase activity as an indicator of an individual's stress levels in a forest environment. The circadian rhythm of salivary amylase activity was measured in healthy young male subjects under stress-free conditions. The salivary amylase activity remained relatively constant throughout the day. Salivary amylase activity was then measured before and after walking in both urban and forest environments using a hand-held monitor. Our results indicated that (i) the circadian rhythm fluctuations in salivary amylase activity were much smaller than the stressor-induced variations; (ii) salivary amylase activity was an excellent indicator of the changes in sympathetic nervous activity; and (iii) the forest was a good environment in which people could experience much less environment-derived stress.

Total sleep deprivation effect on disengagement of spatial attention as assessed by saccadic eye movements

Objective Previous research has shown that total sleep deprivation (TSD) of short duration (one night) affects performance to some cognitive tasks subserved by a fronto-parietal network. The aim of our study was to assess the effects of TSD on visuo-spatial attention, which is a cognitive task involving this network. Specifically, the disengagement of spatial attention was investigated with gap and overlap paradigms of saccadic eye movements. Methods Ten healthy young male subjects performed the two tasks the morning after a normal night and after a TSD night. The study was conducted using a balanced, crossover design. Results TSD significantly increased the gap effect (difference of latency between overlap and gap). Conclusions This result can be interpreted as an impaired disengagement of attention after TSD. As the peak velocity, which is an indicator of alertness, was not altered by TSD, the impairment in the disengagement of spatial attention does not result from a decrease in alertness. Significance This study shows that saccadic eye movements enable studying alertness and disengagement of spatial attention simultaneously. The idea that specific brain areas are affected by TSD is confirmed by our results.

Possible Biphasic Sweating Response during Short-term Heat Acclimation Protocol for Tropical Natives

The aim of the present study was to evaluate the sweat loss response during short-term heat acclimation in tropical natives. Six healthy young male subjects, inhabitants of a tropical region, were heat acclimated by means of nine days of one-hour heat-exercise treatments (40+/-0 degrees C and 32+/-1% relative humidity; 50% (.)VO(2peak) on a cycle ergometer). On days 1 to 9 of heat acclimation whole-body sweat loss was calculated by body weight variation corrected for body surface area. On days 1 and 9 rectal temperature (T(re)) and heart rate (HR) were measured continuously, and rating of perceived exertion (RPE) every 4 minutes. Heat acclimation was confirmed by reduced HR (day 1 rest: 77+/-5 b.min(-1); day 9 rest: 68+/-3 b.min(-1); day 1 final exercise: 161+/-15 b.min(-1); day 9 final exercise: 145+/-11 b.min(-1), p<0.05), RPE (13 vs. 11, p<0.05) and T(re) (day 1 rest: 37.2+/-0.2 degrees C; day 9 rest: 37.0+/-0.2 degrees C; day 1 final exercise: 38.2+/-0.2 degrees C; day 9 final exercise: 37.9+/-0.1 degrees C, p<0.05). The main finding was that whole-body sweat loss increased in days 5 and 7 (9.49+/-1.84 and 9.56+/-1.86 g.m(-2).min(-1), respectively) compared to day 1 (8.31+/-1.31 g.m(-2).min(-1), p<0.05) and was not different in day 9 (8.48+/-1.02 g.m(-2).min(-1)) compared to day 1 (p>0.05) of the protocol. These findings are consistent with the heat acclimation induced adaptations and suggest a biphasic sweat response (an increase in the sweat rate in the middle of the protocol followed by return to initial values by the end of it) during short-term heat acclimation in tropical natives.

Effects of short-term folic acid and/or riboflavin supplementation on serum folate and plasma total homocysteine concentrations in young Japanese male subjects

To investigate the effects of short-term folic acid and/or riboflavin supplementation on serum folate and plasma plasma total homocysteine (tHcy) concentrations in young Japanese male subjects. In a double blind, randomized controlled trial. Subjects were randomly assigned to one of four groups and received a placebo (control group), 800 microg/day folic acid (FA group), 8.4 mg/day riboflavin (R group), or both (FAR group) for 2 weeks. Tokyo, Japan. In total, 32 healthy male volunteers aged 20-29 years. At the end of the 2 week supplementation period, the tHcy concentration decreased significantly in the FA group. Serum folate concentrations had increased between 2.7 and 2.0-fold in the FA and FAR groups, respectively, but the mean within-group changes in serum folate and plasma tHcy concentrations did not differ between these two groups. At the end of the study, alanine amino transferase was decreased in the R and FAR groups, while alanine amino transferase was increased in the FA group. Supplementation with folic acid, 800 microg/day, for 2 weeks, increased the serum and red blood cell folate concentrations and decreased the plasma tHcy concentrations in healthy young male subjects. Riboflavin supplementation may have blunted the effect of folic acid, which resulted in a diminished reduction of tHcy in our subjects.

Maintaining rotational equilibrium during object manipulation: linear behavior of a highly non-linear system

We address issues of simultaneous control of the grasping force and the total moment of forces applied to a handheld object during its manipulation. Six young healthy male subjects grasped an instrumented handle and performed its cyclic motion in the vertical direction. The handle allowed for setting different clockwise (negative) or counterclockwise torques. Three movement frequencies: 1, 1.5 and 2 Hz, and five different torques: -1/3, -1/6, 0, 1/6 and 1/3 Nm, were used. The rotational equilibrium was maintained by two means: (1) Concerted changes of the moments produced by the normal and tangential forces, specifically anti-phase changes of the moments during the tasks with zero external torque and in-phase changes during the non-zero-torque tasks, and (2) Redistribution of the normal forces among individual fingers such that the agonist fingers--the fingers that resist external torque--increased the force in phase with the acceleration, while the forces of the antagonist fingers--those that assist the external torque--especially, the fingers with the large moment arms, the index and little fingers, stayed unchanged. The observed effects agree with the principle of superposition--according to which some complex actions, for example, prehension, can be decomposed into elemental actions controlled independently--and the mechanical advantage hypothesis according to which in moment production the fingers are activated in proportion to their moment arms with respect to the axis of rotation. We would like to emphasize the linearity of the observed relations, which was not prescribed by the task mechanics and seems to be produced by specific neural control mechanisms.

Enhanced cerebral CO2 reactivity during strenuous exercise in man

Light and moderate exercise elevates the regional cerebral blood flow by approximately 20% as determined by ultrasound Doppler sonography (middle cerebral artery mean flow velocity; MCA V(mean)). However, strenuous exercise, especially in the heat, appears to reduce MCA V(mean) more than can be accounted for by the reduction in the arterial CO(2) tension (P(a)CO(2)). This study evaluated whether the apparently large reduction in MCA V(mean) at the end of exhaustive exercise relates to an enhanced cerebrovascular CO(2) reactivity. The CO(2) reactivity was evaluated in six young healthy male subjects by the administration of CO(2) as well as by voluntary hypo- and hyperventilation at rest and during exercise with and without hyperthermia. At rest, P(a)CO(2) was 5.1 +/- 0.2 kPa (mean +/- SEM) and MCA V(mean) 50.7 +/- 3.8 cm s(-1) and the relationship between MCA V(mean) and P(a)CO(2 )was linear (double-log slope 1.1 +/- 0.1). However, the relationship became curvilinear during exercise (slope 1.8 +/- 0.1; P < 0.01 vs. rest) and during exercise with hyperthermia (slope 2.3 +/- 0.3; P < 0.05 vs. control exercise). Accordingly, the cerebral CO(2) reactivity increased from 30.5 +/- 2.7% kPa(-1) at rest to 61.4 +/- 10.1% kPa(-1) during exercise with hyperthermia (P < 0.05). At exhaustion P(a)CO(2) decreased 1.1+/- 0.2 kPa during exercise with hyperthermia, which, with the determined cerebral CO(2) reactivity, accounted for the 28 +/- 10% decrease in MCA V(mean). The results suggest that during exercise changes in cerebral blood flow are dominated by the arterial carbon dioxide tension.

β1-Adrenoceptor Mediated Origin of the Heart Rate Performance Curve Deflection

The deflection of the HR performance curve (HRPC) has been described as an objective marker of submaximal exercise performance. HR response to incremental cycle ergometer exercise is shown to be neither linear nor uniform and a physiological explanation of the deflection phenomenon is lacking. We hypothesized that differences in the beta1-adrenoceptor site are the source of these differences. The aim of the study was to investigate the influence of the highly selective beta1-adrenoceptor (beta1-AR) antagonist bisoprolol (Bi) on the HRPC in young healthy male subjects with different HR response patterns. Sixteen subjects were treated in randomized order with Bi or a placebo (Pl) in two separate trials. HR response during incremental cycle ergometer exercise was compared between the two trials. Blood lactate concentration (La) and ventilatory variables were measured throughout both tests. Bi changed the direction of the HRPC more in subjects with a regular, s-shaped response pattern under placebo than those with a nonregular or linear pattern. The influence of Bi on the HR at the second lactate turn point was significantly related (R = 0.78; P < 0.001) to the pattern of the HRPC in Pl conditions. We suggest that differences between the subjects with regular s-shaped versus nonregular HRPC may be due to differences at the beta1-AR site. The origin of the HRPC deflection is mediated in part by the beta1-AR sensitivity.

Urinary and Blood Concentrations of β2-Agonists in Trained Subjects: Comparison between Routes of Use

We aimed to assess the plasma and urine concentrations of beta2-agonists and evaluate the difference between three routes of administration in trained adults in order to distinguish doping from prevention of exercise-induced asthma. Ten young healthy Caucasian male subjects received during a four treatment period study: 1) inhaled salbutamol (S(I)) 2 x 100 microg t.i.d. for 3 days, 2) inhaled formoterol (F(I)) 2 x 12 microg b.i.d. for 3 days, 3) a single subcutaneous injection of salbutamol (S(S)) 0.5 mg, and 4) salbutamol 2 x 2 mg t.i.d. orally for 3 days (S(O)). Blood samples were taken during the first and the third day of experimentation at baseline, 30 min, 1 h, 2 h, 4 h and 6 h after administration; additional blood samples were drawn at 15 min for S(I), S(S) and F(I) and at 12 h for F(I). Urinary samples were collected at baseline, 2 h, 4 h, 6 h and 12 h after administration. Urinary concentrations were 20 to almost 50 times higher after S(O) than after S(I). Mean urinary concentration after S(O) increased to above 800 ng.mL(-1) within the two hours and above 1000 ng.mL(-1) at 6 to 12 hours post-drug administration. Urinary concentrations after S(S) were maximal during the first 2 hours (mean: 340 +/- 172 ng.mL(-1)). Plasma concentrations were very low, whatever the routes of administration. Results showed that we could eliminate the use of S(I) (authorized) and S(S) administration when individual urinary concentrations are higher than 230 ng.mL(-1) and 615 ng.mL(-1), respectively. Therefore, at rest, the cut-off value used to discriminate therapeutic from doping salbutamol intake could be fixed at 250 ng.mL(-1) instead of the 1000 ng.mL(-1) still authorized by international committees.

Latency of auditory P300 correlates with self‐control as measured by the Sixteen Personality Factor Questionnaire

The reception, processing, and storage of information about experience define personality. The present study investigated the relationship between auditory event-related potentials (AERP) and personality traits. The AERP were recorded using a standard auditory oddball paradigm, and personality was evaluated by Cattell's Sixteen Personality Factor Questionnaire (16PF) in 20 healthy young male subjects. The P300 latency was found to be significantly associated with rule consciousness (factor G in the 16PF), perfectionism (factor Q3), and self-control (factor SC): it was negatively correlated with G score (r = -0.56, P = 0.01), Q3 score (r = -0.67, P = 0.001), and SC score (r = -0.65, P = 0.002). Moreover, the P300 amplitude and N100 amplitude were negatively correlated with reasoning (factor B; r = -0.46, P = 0.044; and r = -0.72, P = 0.002, respectively). These results indicate that the personality traits of self-control, perfectionism, high superego, and reasoning are related to information processing in the brain.

Cholinergic enhancement of episodic memory in healthy young adults

Acetylcholine esterase (AchE) inhibitors are known to remediate symptoms of Alzheimer's disease. However, only few systematic data exist on the effects of cholinergic treatment on cognitive functions in normal subjects. This study evaluated the effects of donepezil, an inhibitor of AchE, on cognitive performance in young and healthy subjects. We used a randomised double-blind parallel group placebo-controlled repeated measures design to investigate changes of cognitive functions in a group of 30 young healthy male subjects (mean age 23.9 years+/-2.24 SD) upon application of donepezil or placebo for 30 days. Attentional and executive functions, visual and verbal short-term and working memory, semantic memory, as well as verbal and visual episodic memory were investigated using an extensive neuropsychological test battery. Time-by-group interactions demonstrated significant drug effects that were specific to episodic memory in both the verbal and visual domain. Additionally, donezepil significantly improved long-term visual episodic recall. In none of the other functions under investigation any significant treatment effects were observed. Given this specific drug effect and the well-known relevance of the hippocampal region for episodic memory, we conclude that this region appears to be the major target of cholinergic enhancement in healthy subjects due to long-term inhibition of AchE.

Reliability of maximal muscle force and voluntary activation as markers of exercise-induced muscle damage

The loss of the ability of skeletal muscle to generate force is one of the most appropriate and valid means to quantify muscle damage. Routine measurements of maximal muscle force, however, include many potential sources of error, the most important of which may be a possible lack of central drive to the muscles. The aim of the present study was to determine the reliability of maximal isometric quadriceps muscle force and voluntary activation over a time scale that is typically employed to examine the aetiology of exercise-induced muscle damage. We also attempted to characterise the reliability of several twitch interpolation variables including the size of the interpolated twitch and the state (i.e. un-potentiated vs potentiated) and size of the resting twitch. Over a 7-day period, eight healthy active males performed repeated maximal voluntary isometric contractions (MVC) of the quadriceps (baseline and 2 h, 6 h, 24 h, 48 h, 72 h and 7 days post). Systematic variations in maximal muscle force, voluntary activation, interpolated twitch, un-potentiated twitch and potentiated twitch were not statistically significant (P>0.05) and 95% repeatability coefficients of +/-76.03 N, +/-4.42%, +/- 8.44 N, +/-25.92 N and +/-43.58 N were observed, respectively. These data indicate that young healthy well-familiarized male subjects can reproduce their perceived maximal efforts both within and between days where activation levels of >90% are routinely achieved. Providing activation remains within these limits in the 7 days following an acute bout of exercise, the researcher would be 95% certain that exercise-induced muscle damage is present in individual subjects (taken from similar subject populations) if MVC force falls outside these limits.

Heart Rate Performance Curve And Arg389gly ?? 1???adrenoceptor Polymorphism

Differences in ß 1-adrenoceptor (AR) sensitivity were described to explain different response patterns of the Heart Rate Performance Curve (HRPC) (MSSE 33, 2001, 5: S202). PURPOSE The purpose of the study was to investigate if the Arg389Gly ß 1- adrenoceptor polymorphism is related to different patterns of the HRPC. METHODS 164 young healthy male sports students participated in the study. Incremental cycle ergometer exercise (40 W start, 20W/min increase) was performed in all subjects to obtain the heart rate performance (HRPC) and to determine the different HR patterns by means of the degree and the direction of deflection (kHR) of the HRPC. The ß 1-adrenoceptor Arg389Gly polymorphism was determined from venous blood samples according to published standards. ANOVA was calculated to describe differences of kHR between the three genetic variants. RESULTS The number of subjects presenting different variants was 83 (AA), 73 (AG) and 8 (GG). kHR was found at 0.29±0.34 (AA), 0.37±0.36 (AG) and 0.37±0.37 (GG). No significant difference was found for kHR between the different polymorphisms, however a trend to lower values in the AA variant was found. CONCLUSION As previously reported the Arg389Gly ß 1-AR polymorphism had no significant functional relationship with HR response to incremental cycle ergometer exercise in young healthy male subjects.