Differences in the oxygenation of the forearm muscle during isometric contraction in trained and untrained subjects

The aim of this study was to test a hypothesis that a longer duration of isometric contraction is related to an increased oxygenation status of the muscle. A group of trained rock climbers and untrained subjects performed 15 kp sustained isometric contraction until fatigue set in. The oxygenation status was assessed using near infrared spectroscopy (ISS, USA). The results support the hypothesis. The concentration of relative oxygenated hemoglobin was higher in the rock climbers than in the untrained subjects. The relative total hemoglobin did not differentiate the two groups enough to show that blood volume also strongly influences contraction time.     

Changes in movement variability and task performance during a fatiguing repetitive pointing task

Changes in neuromuscular strategies employed with fatigue during multi-joint movements are still poorly understood. Studies have shown that motor variability of individual joints increases when performing upper limb tasks to fatigue, while movement parameters related to the task goal remain constant. However, how the inter-limb coordination and its variability change during specific movement phases with fatigue is still unclear. The aim of this study was to assess the effects of neck-shoulder fatigue on shoulder and elbow kinematic variabilities, shoulder-elbow coordination and its variability, and endpoint characteristics during different phases of a forward pointing movement. Nineteen healthy young adults continuously performed a repetitive pointing task until fatigue (Borg rating of 8/10). Changes in elbow-shoulder coordination through the movement were assessed using the continuous relative phase and statistical nonparametric mapping methods. At the end of the task, muscle fatigue was evidenced by significant increases in anterior deltoid (+13%) and biceps brachii (+30%) activity. Shoulder horizontal abduction, elbow flexion variability and shoulder-elbow coordination variability were increased with fatigue at different moments of the movement cycle (shoulder: during the first 17% and most of the second half movement, elbow: from 73% to 91%, coordination: almost the whole movement). However, movement timing errors and endpoint spatial variability were mostly preserved, even with fatigue. We showed that increased variability with fatigue is not only observed in the fatigued joint (shoulder), but also in the elbow and shoulder-elbow coordination, and may have a goal of preserving global task performance.     

Renal blood volume regulation in trained and untrained subjects during immersion

To study the cause of the increased blood volume of endurance-trained athletes we assessed the renal blood volume regulating mechanisms in eight untrained (UT) and eight endurance-trained (TR) male subjects during a 4 h head-out immersion. In TR plasma volume remained constant whereas it decreased in UT by 2.4 ml/kg (p less than 0.025). Immersion diuresis of TR was only half as high as in UT (peak values: 3.22 ml/min in UT, 1.60 ml/min in TR). Free water clearance remained approximately constant in UT but temporarily decreased in TR (p less than 0.001). This points to poor or even absent inhibition of antidiuretic hormone secretion in the latter group. Osmolar clearance increased less in TR than in UT (p less than 0.02) which was partly due to a delayed increase of glomerular filtration rate. Plasma osmolality, creatinine, and protein concentrations as well as hematocrit values were reduced during immersion to a similar extent in both groups. The results indicate a reduced renal response of endurance-trained subjects to congestion of the low-pressure system resulting in an increase in blood volume.     

EMG versus oxygen uptake during cycling exercise in trained and untrained subjects.

The aim of this study was to test the hypothesis that bicycle training may improve the relationship between the global SEMG energy and VO2. We already showed close adjustment of the root mean square (RMS) of the surface electromyogram (SEMG) to the oxygen uptake (VO2) during cycling exercise in untrained subjects. Because in these circumstances an altered neuromuscular transmission which could affect SEMG measurement occurred in untrained individuals only, we searched for differences in the SEMG vs. VO2 relationship between untrained subjects and well-trained cyclists. Each subject first performed an incremental exercise to determine VO2max and the ventilatory threshold, and second a constant-load threshold cycling exercise, continued until exhaustion. SEMG from both vastus lateralis muscles was continuously recorded. RMS was computed. M-Wave was periodically recorded. During incremental exercise: (1) a significant non-linear positive correlation was found between RMS increase and VO2 increase in untrained subjects, whereas the relationship was best fitted by a straight line in trained cyclists; (2) the RMS/VO2 ratio decreased progressively throughout the incremental exercise, its decline being significantly and markedly accentuated in trained cyclists; (3) in untrained subjects, significant M-wave alterations occurred at the end of the trial. These M-wave alterations could explain the non-linear RMS increase in these individuals. During constant-load exercise: (1) after an initial increase, the VO2 ratio decreased progressively to reach a plateau after 2 min of exercise, but no significant inter-group differences were noted; (2) no M-wave changes were measured in the two groups. We concluded that the global SEMG energy recorded from the vastus lateralis muscle is a good estimate of metabolic energy expenditure during incremental cycling exercise only in well-trained cyclists.     

Oxygen dissociation curves in trained and untrained subjects.

Oxygen dissociation curves (ODC) in whole blood and organic phosphate concentrations in red cells were determined in 10 highly trained male athletes (TR), 6 semitrained subjects (ST) who played sports regularly at low intensities and 8 untrained people (UT). In all groups standard ODCs (37 degrees C, pH 7.40, PCO2 approximately 43 Torr) at rest and after a short exhaustive exercise were nearly identical, but PO2 values measured immediately after blood sampling and corrected to standard conditions tended to fall to the right of the in vitro ODC. Elevated P50 in the physically active [28.65 +/- 1.4 Torr (3.81 +/- 0.18 kPa) in ST, 28.0 +/- 1.1 Torr (3.73 +/- 0.15 kPa) in TR, but 26.5 +/- 1.1 Torr (3.53 +/- 0.15 kPa) in UT] were partly caused by different [DPG] (11.9 +/- 1.3 mumol/GHb in UT, 13.3 +/- 1.5 mumol/GHb in TR, 13.8 +/- 2.2 mumol/gHb in ST). There were remarkable differences in the shape of the curves between the groups. The slope "n" in the Hill plot amounted to 2.65 +/- 0.12 in UT, 2.74 +/- in ST and 2.90 +/- 0.11 in the TR (2 p against UT less than 0.001), leading to an elevated oxygen pressure of about 2 Torr (0.27 kPa) at 20% saturation and an augmented oxygen extraction of 5--7 SO2 at a PO2 of about 15 Torr (2kPa), which might be favorable at high workloads. The reason for the phenomenon could be an increased amount of young red cells in the blood of TR, caused by exercise induced hemolysis.     

Phosphate determination during hypokinesia and ambulation in establishing phosphate changes in trained and untrained subjects

Hypokinesia (diminished movement) induces phosphate (P) changes; however, it is not known if P change is greater in trained than untrained subjects. Measuring P balance and P retention during hypokinesia (HK) and P load, we studied if changes in P retention and P depletion were significantly (p<0.05) greater in trained than untrained subjects. Studies were done during a 30-d pre-HK period and a 364-d HK period. Forty male trained and untrained healthy individuals aged 24.5±5.4 yr were chosen as subjects. All volunteers were equally divided into four groups: trained ambulatory control subjects (TACS), trained hypokinetic subjects (THKS), untrained ambulatory control subjects (UACS), and untrained hypokinetic subjects (UHKS). All THKS and UHKS were limited to an average walking distance of 0.3 km/d, and TACS and UACS were on an average running distance of 9.8 and 1.8 km/d, respectively. Subjects took daily 12.7-mmol dicalcium-phosphate/kg body weight in the form of supplementation. Negative P balance, fecal P loss, urinary P and calcium (Ca) excretion, serum P, and total Ca (Ca_t) levels increased significantly (p<0.05), whereas P retention, serum 1,25-dihydroxyvitamin D [1,25 (OH)₂D₃] and intact parathyroid hormone (iPTH) level decreased significantly (p<0.05) in THKS and UHKS when compared with their pre-HK values and their respective ambulatory controls (TACS and UACS). However, P retention, P balance, serum, urinary, and fecal P, and serum hormone level changed significantly (p<0.05) more in THKS than UHKS. Retention of P, fecal P, urinary P and Ca loss, serum P and Ca_t level, P balance, 1,25(OH)₂D₃, and iPTH level change insignificantly (p>0.05) in TACS and UACS when compared with their pre-HK control values. It was concluded that significant negative P balance may indicate P depletion, whereas significant P loss in spite of negative P balance and P load may suggest P retention incapacity; however, P depletion was greater in THKS than UHKS. Clearly, P is wasted much more in THKS than UHKS.     

Differences in performance between trained and untrained subjects during a 30-s sprint test in a wheelchair ergometer

To compare physiological responses and propulsion technique of able bodied subjects with no prior experience of wheelchairs (AB) and wheelchair dependent subjects (WD), ten AB and nine WD performed a 30-s sprint test in a wheelchair ergometer. The WD had spinal cord injuries with a lesion at T8 or lower. The WD and AB did not show significantly different physiological responses. The power values averaged for the right wheel over the 30 s of the test were 50.2 (SD 14.7) W and 48.0 (SD 4.4) W for WD and AB, respectively. No significant differences in torque application could be discerned, although WD subjects seemed to have a more flattened torque curve with a smaller negative deflection at the beginning of the push. The WD applied a significantly higher horizontal propulsive force to the handrims but did not apply force more effectively. The percentages of effective force to total propulsive force were 61 (SD 16)% for WD and 57 (SD 4)% for AB. With regard to the kinematic parameters, AB followed the handrims significantly longer than WD (end angle AB 65°, WD 44°), started the push phase with their arms more in retroflexion and flexed their trunks further forward. The AB did however show a movement pattern comparable to that of wheelchair athletes measured in a comparable experiment. It could not be decided conclusively that inexperience in wheelchair propulsion led to a less effective propulsion technique. Despite the selection of WD with respect to lesion level, interindividual differences in terms of level of training may have been responsible for the absence of significant results.     

Transfer effects in endurance exercise. Adaptations in trained and untrained muscles

The effects of 8 weeks of bicycle endurance training (5 X /week for 30 min) on maximal oxygen uptake capacity (VO2max) during arm and leg ergometry, and on the ultrastructure of an untrained arm muscle (m. deltoideus), and a trained leg muscle (m. vastus lateralis) were studied. With the training, leg-VO2max for bicycling increased by +13%, while the capillary per fiber ratio and the volume density of mitochondria in m. vastus lateralis increased by +15% and +40%, respectively. In contrast, the untrained m. deltoideus showed an unchanged capillary per fiber ratio and a decreased mitochondrial volume density (-17%). Despite this decrease of mitochondrial volume arm-VO2max increased by +9%. It seems unlikely that the observed discrepancy can be explained by cardiovascular adaptations, since arm cranking did not fully tax the cardiovascular system (arm-VO2max/leg-VO2max: 0.74 and 0.71 before and after training, respectively). Thus neither cardiovascular adaptations nor local structural changes in the untrained muscles could explain the increased arm-VO2max. However, the enhanced capacity for lactate clearance after endurance training could be sufficient to account for the larger VO2max during arm cranking. We propose that an increased net oxidation of lactate might be responsible for the increased arm-VO2max found after bicycle endurance training.     

Proteomic analysis and protein carbonylation profile in trained and untrained rat muscles

Understanding the relationship between physical exercise, reactive oxygen species and skeletal muscle modification is important in order to better identify the benefits or the damages that appropriate or inappropriate exercise can induce. Unbalanced ROS levels can lead to oxidation of cellular macromolecules and a major class of protein oxidative modification is carbonylation. The aim of this investigation was to study muscle protein expression and carbonylation patterns in trained and untrained animal models. We analyzed two muscles characterized by different metabolisms: tibialis anterior and soleus. Whilst tibialis anterior is mostly composed of fast-twitch fibers, the soleus muscle is mostly composed of slow-twitch fibers. By a proteomic approach we identified 15 protein spots whose expression is influenced by training. Among them in tibialis anterior we observed a down-regulation of several glycolitic enzymes. Concerning carbonylation, we observed the existence of a high basal level of protein carbonylation. Although this level shows some variation among individual animals, several proteins (mostly involved in energy metabolism, muscle contraction, and stress response) appear carbonylated in all animals and in both types of skeletal muscle. Moreover we identified 13 spots whose carbonylation increases after training.     

Red cell hemoglobin, hydrogen ion and electrolyte concentrations during exercise in trained and untrained subjects

Red cell concentrations of hemoglobin (MCHC), H+, Na+, K+, Mg++, cl- were measured in femoral venous blood of six untrained (UT), six endurance trained (TR) and three semitrained (ST) subjects during graded increasing work (4, 8, 12, 18 and 24 mkp/s, 10-15 min on each step) on a bicycle ergometer. Before exercise no significant differences were detected for the measured variables when comparing UT and TR. During exercise MCHC, [Na+], [K+] and [Mg++] remained constant indicating lack of water shift into the erythrocytes in spite of a marked acidosis (lowest pH Blood value 7.225). This lack resulted from an elevated extracellular osmolality. [H+]Ery and [Cl-]Ery maximally increased by 2.0 X 10(-8) eq/kg H2O and 10 meq/l, respectively. The change was markedly greater in UT than in TR at equal load. However, if [H+] Ery and [Cl-] Ery were related to pH of whole blood, differences between groups, almost disappeared and the ions were distributed as predictable from in vitro experiments (Fitzsimmons and Sendroy, 1961). Behaviour of H+ and Cl- may be of importance for oxygen dissociation under in vivo conditions.     

Changes in surface EMG parameters during static and dynamic fatiguing contractions.

The effect of contraction types on muscle fiber conduction velocity (MFCV), median frequency (MDF) and mean amplitude (AMP) of surface electromyography was examined in the vastus lateralis of 19 healthy male adults. The subjects performed knee extension both statically and dynamically until they were exhausted. The static contraction was a sustained isometric extension of the knee at a joint angle of 90 degrees with 50% of the maximum voluntary contraction (MVC) load. The dynamic contraction was a repetitive isotonic extension of the knee between the angles of 90 degrees and 180 degrees with the same 50% MVC load at a frequency of 10 times per minute. MFVC during the static contraction significantly decreased during the exercise (p < 0.01). On the other hand, MFVC during the dynamic contraction did not significantly change throughout the exercise. MDF decreased and AMP increased during both types of contractions (p < 0.01). Because the blood flow within the muscle is maintained during the dynamic contraction by enhanced venous return from the contracting muscle, these results suggested that MFVC is affected by the metabolic state in the muscle and the changes in MDF cannot be explained only by that of MFVC.     

Excess postexercise oxygen consumption and recovery rate in trained and untrained subjects

Short, Kevin R., and Darlene A. Sedlock. Excesspostexercise oxygen consumption and recovery rate in trained anduntrained subjects. J. Appl. Physiol.83(1): 153-159, 1997.The purpose of this study was todetermine whether aerobic fitness level would influence measurements ofexcess postexercise oxygen consumption (EPOC) and initial rate ofrecovery. Twelve trained [Tr; peak oxygen consumption(O_{2 peak}) = 53.3 ± 6.4 ml · kg¹ · min¹]and ten untrained (UT;O_{2 peak} = 37.4 ± 3.2 ml · kg¹ · min¹)subjects completed two 30-min cycle ergometer tests on separate days inthe morning, after a 12-h fast and an abstinence from vigorous activityof 24 h. Baseline metabolic rate was established during the last 10 minof a 30-min seated preexercise rest period. Exercise workloads weremanipulated so that they elicited the same relative, 70%O_{2 peak} (W70%), orthe same absolute, 1.5 l/min oxygen uptake(O₂) (W1.5), intensity forall subjects, respectively. RecoveryO₂, heart rate (HR), andrespiratory exchange ratio (RER) were monitored in a seated positionuntil baseline O₂ wasreestablished. Under both exercise conditions, Tr had shorter EPOCduration (W70% = 40 ± 15 min, W1.5 = 21 ± 9 min) than UT(W70% = 50 ± 14 min; W1.5 = 39 ± 14 min), but EPOC magnitude(Tr: W70% = 3.2 ± 1.0 litersO₂, W1.5 = 1.5 ± 0.6 liters O₂; UT: W70% = 3.5 ± 0.9 liters O₂, W1.5 = 2.4 ± 0.6 liters O₂) was not different between groups. The similarity of Tr and UT EPOCaccumulation in the W70% trial is attributed to the parallel declinein absolute O₂ during mostof the initial recovery period. Tr subjects had faster relative declineduring the fast-recovery phase, however, when a correction for theirhigher exerciseO₂ was taken.Postexercise O₂ was lowerfor Tr group for nearly all of the W1.5 trial and particularly duringthe fast phase. Recovery HR kinetics were remarkably similar for bothgroups in W70%, but recovery was faster for Tr during W1.5. RER valueswere at or below baseline throughout much of the recovery period in both groups, with UT experiencing larger changes than Tr in both trials. These findings indicate that Tr individuals have faster regulation of postexercise metabolism when exercising at either thesame relative or same absolute work rate.

     

Muscle fiber types and size in trained and untrained muscles of elite athletes

Tissue samples were obtained from vastus lateralis and deltoid muscles of physical education students (n = 12), Greco-Roman wrestlers (n = 8), flat-water kayakers (n = 9), middle- and long-distance runners (n = 9), and olympic weight and power lifters (n = 7). Histochemical stainings for myofibrillar adenosinetriphosphatase and NADH-tetrazolium reductase were applied to assess the relative distribution of fast-twitch and slow-twitch (ST) muscle fiber types and fiber size. The %ST was not different in the vastus (mean SD 48 +/- 14) and deltoid (56 +/- 13) muscles. The %ST was higher (P less than 0.001), however, in the deltoid compared with vastus muscle of kayakers. This pattern was reversed in runners (P less than 0.001). The %ST of the vastus was higher (P less than 0.001) in runners than in any of the other groups. The %ST of the deltoid muscle was higher in kayakers than in students, runners (P less than 0.001), and lifters (P less than 0.05). The mean fiber area and the area of ST fibers were greater (P less than 0.01) in the vastus than the deltoid muscle. Our data show a difference in fiber type distribution between the trained and nontrained muscles of endurance athletes. This pattern may reflect the adaptive response to long-term endurance training.