Respiratory muscle function in trained and untrained adolescents during short-term high intensity exercise

Summary The breathing pattern and respiratory muscle function were investigated in ten trained and ten untrained adolescents (aged 15–16 years) while undergoing an incremental intensity exercise test on a cycle ergometer up to 80% maximal oxygen consumption ( O_2max), maintained to exhaustion. Before and after exercise, maximal inspiratory (P _{I max}) and expiratory (P _{E max}) pressures were measured at residual volume and total lung capacity, respectively. During exercise, the breathing pattern [tidal volume (V _T), respiratory frequency (f _R), ventilation] and the relative contribution of ribcage and abdomen to V _T were assessed using inductance plethysmography. Electromyographic activities of transversus abdominis (EMG_tr) and diaphragm (EMG_di) muscles were recorded and analysed during exercise. There was a difference in the change in the pattern of breathing between the trained and the untrained group; f _R increased significantly (P < 0.05) at 40% O_2maxfor the untrained group. Before exercise there was no difference in the maximal respiratory pressures. Up to 60% and 80% O_2max, transversus abdominis and diaphragm muscle activity increased significantly in the trained adolescents. However in this group, no evidence of respiratory muscle fatigue appeared: P _{I max}, P _{E max} and the frequency spectrum of EMG_tr and EMG_di were not altered by exercise up to exhaustion. In the untrained group, who had high ventilatory responses, expiratory muscle function was unchanged at the end of the exercise, but signs of inspiratory muscle fatigue appeared in that P _{I max} was significantly decreased after exercise.     

Effect of bovine colostrum supplementation on the composition of resistance trained and untrained limbs in healthy young men

This study examined the effect of bovine colostrum (BC) supplementation on the tissue composition of resistance trained (T) and untrained (UT) limbs. Using a double-blind design, subjects were randomly allocated to 60 g day^–1 of BC (n=17) or whey protein (WP) (n=17) during 8 weeks of resistance training of the elbow flexors (EF) of their non-dominant arm (T). Axial magnetic resonance images of both upper arms, maximal voluntary isometric torque (MVC) of EF, and the one repetition maximum (1RM) for bicep curls were measured pre- and post-supplementation. There were no differences in macronutrient intakes (P>0.28) or the volume of training completed by T (P=0.98) between the two groups. T of BC experienced a significantly greater increase in circumference [BC 2.3 (3.0)%, WP 0.0 (4.2)%; P=0.05] and cross-sectional area (CSA) [BC 4.2 (6.0)%, WP –0.2 (8.3)%; P=0.05] compared with WP, due principally to a greater increase in skin and subcutaneous fat (SSF) CSA [BC 5.5 (10.9)%, WP –2.7 (14.1)%; P=0.03]. No tissue compartment changed significantly in UT of either group (P>0.05). MVC and 1RM increased for T and UT in both groups (P<0.05), but the increases were not different between groups (P>0.32). Since the SSF compartment increased in T but not UT, and fat turnover in adipocytes is under hormonal control and would not be localised to one arm, we suggest that the increase in SSF CSA in T of BC may have been due to an increase in skin CSA, rather than fat.     

Skeletal muscle of trained and untrained paraplegics and tetraplegics

The effect of physical conditioning on skeletal muscle of individuals with spinal cord injuries (SCI) has been investigated. The anterior portion of the deltoid muscle (active in wheel-chair propulsion) of untrained and endurance-trained paraplegics and tetraplegics, as well as that of untrained able-bodied subjects, was studied. The characterization involved fibre type distribution, capillarization, fibre areas and also oxidative and glycolytic enzyme levels. A general trend towards a successively higher proportion of type I fibres and lower proportion of type IIB fibres was noted in the order of able-bodied subjects (type I, 42%; type IIB, 41%, n=8), paraplegics (type I, 57%; type IIB, 13%, n=13) and tetraplegics (type I, 74%; type IIB, 4.5%, n=11). The trained SCI groups had significantly higher levels of the citric acid cycle marker enzyme citrate synthase (34% and 63%) than the untrained SCI groups and able-bodied subjects, respectively. The glycolytic marker enzyme 6-phosphofructokinase was 32% lower in the tetraplegic groups than in the other groups. In contrast, the fatty acid oxidation marker enzyme 3-hydroxyacyl-CoA dehydrogenase was markedly higher in the tetraplegic group than in the able-bodied subjects (58%) and tended to be higher (21%, P<0.1) than in the paraplegic group. The trained SCI groups displayed significantly higher (28%) levels of capillaries per fibre than the untrained SCI groups, which had about the same levels as the untrained able-bodied subjects. It is concluded that several of the findings are in line with normal muscular adaptation, whereas others are unexpected and support a hypothesis that some of the findings might be due to differences between the groups in, for instance, hormone levels or in types of muscular load.     

Skeletal muscle sympathetic activity at rest in trained and untrained subjects

The effect of physical training on muscle sympathetic activity (MSA) was studied by comparing resting levels of MSA in 8 well-trained racing cyclists and in 8 age-matched untrained subjects (mean age 22 yrs). In addition, MSA was determined for 5 untrained subjects before and after an 8-week training program on cycle erogmeters (training group). Recordings were made from the peroneal nerve at the knee with the subject in recumbent position. The well-trained cyclists were characterized by a clearly higher maximal oxygen uptake (VO₂ max) and lower heart rate at submaximal exercise (180 W) than their untrained counterparts. These variables were also significantly changed with training in the training group. In contrast, there were no training-related effects on MSA. Thus, MSA expressed as either the number of sympathetic bursts/100 heart beats (+2%, NS) or bursts/min (-10%, NS) did not differ between the well-trained cyclists and the untrained controls. Furthermore, no changes in MSA occurred with training in the training group (bursts/100 heart beats: +8%, NS; bursts/min -2%, NS). Individual variations in MSA were large and independent of training state. It is concluded that differences in physical conditioning do not account for the large inter-individual differences in MSA in resting man.     

Buffer capacity and lactate accumulation in skeletal muscle of trained and untrained men

Buffer capacity (β) of skeletal muscle has been determined in trained (n=7) and in sedentary subjects (n=8). The trained subjects were active in ball games where a high degree of anaerobic energy utilization is required. Percentage fibre type occurrence in the thigh muscle was not significantly different in the two groups. However, there was a tendency towards a higher proportion of type I (slow-twitch) fibres (61.5±11.6% vs. 50.2±12.5%) and a lower proportion of type IIB fibres (2.1±3.5% vs 14.1±16.3%) in the trained subjects. The proportion of the cross-sectional area of the muscle biopsies that was made up of type I or type II fibres was not different in the two groups. All subjects performed an isometric contraction of the knee extensors to fatigue at 61% of their maximal voluntary contraction force. Muscle biopsies were taken from the quadriceps femoris muscle at rest and immediately after contraction. The buffer capacity of muscle was calculated from: β= (Muscle lactate (work)-Muscle lactate (rest))/(Muscle pH (rest) -Muscle pH (work)). A higher buffer capacity (p<0.05) was observed in the trained subjects (β=194±30 mmolxpH^-1xkg^-1 dry wt.) compared to the sedentary group (β=164±20) (mean±SD). An unexpected finding was that muscle lactate after contraction to fatigue was lower (30%, p<0.01) and muscle pH was higher (6.80±0.06 vs. 6.61±0.12, p<0.01) in the trained subjects than in the sedentary controls. Creatine phosphate stores were almost completely depleted in both groups. Post-exercise lactate values were related to the proportion of type II fibres in the muscle (p<0.01). There was, however, no statistical correlation betwe β and fibre type occurrence (p>0.05). In summary, the present results indicate that skeletal muscle buffer capacity can be changed by training in man. Furthermore, it is concluded that the lower lactate accumulation and pH decline after an isometric contraction to fatigue that was observed in the trained compared to the sedentary subjects is related to the training per se. However, the tendency towards a lower type I (slowtwitch) fibre percentage in the trained subjects is likely to have contributed to the observed differences.     

Pulmonary oxygen uptake and muscle deoxygenation kinetics during recovery in trained and untrained male adolescents

Previous studies have demonstrated faster pulmonary oxygen uptake ( [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} ) kinetics in the trained state during the transition to and from moderate-intensity exercise in adults. Whilst a similar effect of training status has previously been observed during the on-transition in adolescents, whether this is also observed during recovery from exercise is presently unknown. The aim of the present study was therefore to examine [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics in trained and untrained male adolescents during recovery from moderate-intensity exercise. 15 trained (15 ± 0.8 years, [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max} 54.9 ± 6.4 mL kg⁻¹ min⁻¹) and 8 untrained (15 ± 0.5 years, [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } 44.0 ± 4.6 mL kg⁻¹ min⁻¹) male adolescents performed two 6-min exercise off-transitions to 10 W from a preceding “baseline” of exercise at a workload equivalent to 80% lactate threshold; [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} (breath-by-breath) and muscle deoxyhaemoglobin (near-infrared spectroscopy) were measured continuously. The time constant of the fundamental phase of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} off-kinetics was not different between trained and untrained (trained 27.8 ± 5.9 s vs. untrained 28.9 ± 7.6 s, P = 0.71). However, the time constant (trained 17.0 ± 7.5 s vs. untrained 32 ± 11 s, P < 0.01) and mean response time (trained 24.2 ± 9.2 s vs. untrained 34 ± 13 s, P = 0.05) of muscle deoxyhaemoglobin off-kinetics was faster in the trained subjects compared to the untrained subjects. [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics was unaffected by training status; the faster muscle deoxyhaemoglobin kinetics in the trained subjects thus indicates slower blood flow kinetics during recovery from exercise compared to the untrained subjects.     

Oxygen dissociation curves in trained and untrained subjects

Summary 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 C, pH 7.40, Pco₂43 Torr) at rest and after a short exhaustive exercise were nearly identical, but P _o2 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 [28.6±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 mol/gHb in UT, 13.3±1.5 mol/gHb in TR, 13.8±2.2 mol/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±0.12 in ST and 2.90±0.11 in the TR (2 p against UT<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 (2 kPa), 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.A preliminary report was presented at the 49th Meeting of the German Physiological Society [Pflügers Arch. (Suppl.), 373, R 57 (1978)]     

Activities of creatine kinase isoenzymes in single skeletal muscle fibres of trained and untrained rats

Biochemical changes in the creatine kinase isoenzyme compositions in single muscle fibres of different types in rats were induced by endurance running training. Single muscle fibres were dissected from the soleus and extensor digitorum longus muscles of Wistarstrain male rats trained on a motor-driven treadmill for 16 weeks. Each fibre was typed histochemically (SO, slow-twitch oxidative; FOG, fast-twitch oxidative glycolytic; FG, fast-twitch glycolytic), and the activities of total creatine kinase and its four isoenzymes (CK-MM, -MB,-BB, and mitochondrial creatine kinase) were measured. The endurance training did not affect the total creatine kinase activity, but resulted in significantly increased activities of CK-MB and CK-BB in SO and FOG fibres, and the mitochondrial enzyme activity in FOG and FG fibres. Endurance training induced biochemical changes in the isoenzyme compositions, specifically in FOG fibres. These results suggest that changes in creatine kinase isoenzymes with endurance training reflect changes in the energy metabolism in the different muscle fibres, supporting the hypothesis that the different isoenzymes play different roles in energy transduction.     

Lactate disposal in resting trained and untrained forearm skeletal muscle during high intensity leg exercise

Summary At a given oxygen uptake ( O₂) and exercise intensity blood lactate concentrations are lower following endurance training. While decreased production of lactate by trained skeletal muscle is the commonly accepted cause, the contribution from increased lactate removal, comprising both uptake and metabolic disposal, has been less frequently examined. In the present study the role of resting skeletal muscle in the removal of an arterial lactate load (approximately 11 mmol·-l^–1) generated during high intensity supine leg exercise (20 min at approximately 83% maximal oxygen uptake) was compared in the untrained (UT) and trained (T) forearms of five male squash players. Forearm blood flow and the venoarterial lactate concentration gradient were measured and a modified form of the Fick equation used to determine the relative contributions to lactate removal of passive uptake and metabolic disposal. Significant lactate uptake and disposal were observed in both forearms without any change in forearm O₂. Neither the quantity of lactate taken up [UT, 344.2 (SEM 118.8) mol·100 ml^–1; T, 330.3 (SEM 85.3) mol·100 ml^–1] nor the quantity disposed of [UT, 284.0 (SEM 123.3) mol·100 ml^–1, approximately 83% of lactate uptake; T, 300.8 (SEM 77.7) mol·100 ml^–1, approximately 91% of lactate uptake] differed between the two forearms. It is concluded that while significant lactate disposal occurs in resting skeletal muscle during high intensity exercise the lower blood lactate concentrations following endurance training are unlikely to result from an increase in lactate removal by resting trained skeletal muscle.     

The effects of high-intensity exercise on skeletal muscle neutrophil myeloperoxidase in untrained and trained rats

The primary purpose of this study was to examine the effects of high-intensity acute exercise on neutrophil infiltration in different muscle fiber types of untrained rats and to compare postexercise neutrophil accumulation in muscles of untrained and trained animals. The effect of high-intensity acute exercise on blood neutrophil degranulation reaction in trained animals was also elucidated. Neutrophil enzyme myeloperoxidase (MPO) was determined as a measure of neutrophil migration into muscles and blood neutrophil degranulation. Male albino rats were subjected to acute exercise and 5 weeks of training. The used model of intensive acute exercise consisted of 5, 15, and 25 intermittent swimming bouts with the addition of weight (8% of total body mass) for 1-min each, followed by 1.5-min rest intervals. MPO was analyzed in quadriceps muscle (white and red portion) and in soleus muscle 24 h after acute exercise. MPO content in resting blood plasma and neutrophils was determined 48-h following the completion of a training process. In addition, MPO content in the trained rats was measured immediately (in blood plasma and neutrophils) after and 24 h (in muscles) following a single-bout of exercise to exhaustion. The remaining two-third of the trained animals were exposed to a single-bout of nonstop swimming with the addition of 6% body mass until exhaustion. These animals were sacrificed immediately and 24 h after loaded swimming to analyze leukocyte count, MPO content in blood plasma and neutrophils and in muscles, respectively. About 24 h after exercise MPO concentrations in the red portion of quadriceps muscle and in soleus muscle were 4–7-fold higher as compared to the white portion of m. quadriceps. There was an association between the quantity of repetitive bouts of swimming and MPO content in the muscles. The duration of swimming to exhaustion of trained rats was 3.8-fold longer than untrained sedentary control. At rest, plasma MPO concentration was found to be 40% higher in trained rats compared to untrained controls (P < 0.05). Postexercise plasma MPO concentrations were significantly higher both in untrained (+137%; P < 0.05) and trained (+81%; P < 0.05) rats compared to resting values. At rest neutrophil MPO concentration was found to be 33% lower in trained rats compared to untrained controls (P < 0.05). There were no significant differences in muscle MPO concentrations between untrained and trained rats at rest. A single-bout of exercise to exhaustion produced a greater increase in MPO content in untrained compared to trained rats. The data suggest that postexercise neutrophil infiltration is more intensive in red fibers types compared to white fiber types. A smaller neutrophil infiltration in muscles of trained animals after exhaustive exercise suggests a protective effect of previous training to muscle injury.Portions of this paper were presented by V. Morozov in 2003 at the 6th ISEI Symposium on Exercise Muscle Metabolism and Immune Function, Copenhagen.     

Clenbuterol has a greater influence on untrained than on previously trained skeletal muscle in rats

The effects of clenbuterol, a selectiveβ ₂-adrenergic agonist, and of exercise training on the properties of skeletal muscle were studied in the hindlimb of sedentary and trained rats. A 2-week training programme, consisting of climbing on a grid with a load attached to the tail, did not increase the muscle mass of the soleus, the plantaris and the gastrocnemius muscles or modify the isometricin situ contractile properties of the medial gastrocnemius muscle. The only change observed in a 12-week training regimen was a significant increase in contractile forces (expressed in grams per gram of muscle) of the medial gastrocnemius muscle at sub-tetanic stimulating frequencies (twitch 42%, 25Hz 45% and 50Hz 47%). Both training programmes significantly increased fatigue resistance of the medial gastrocnemius muscle. A 2-week oral treatment with clenbuterol significantly increased the muscle mass of the soleus (19.8%), plantaris (16.9%) and gastrocnemius (15.3%) muscles in all animals treated with the agonist. However, clenbuterol had different effects in animals beginning their training programme than in animals that had been trained for the previous 10 weeks. Specifically, clenbuterol caused a significant increase in gastrocnemius muscle mass in the former group but not in the latter. These results suggest that the responses to the combination of clenbuterol and training in previously trained skeletal muscles are not as marked as those observed in untrained muscles.     

Blood flow and tissue-pO2 in the trained and untrained gastrocnemius muscle of the anesthetized guinea pig

In 10 guinea pigs the gastrocnemius muscles on one side were tenotomised. By the tenotomy the daily work load of the gastrocnemius muscle was lowered in the operated leg (“untrained muscles”) and increased in the control leg (“trained muscles”). Before and several weeks after the operation blood flow was measured in the lower legs (by segmental plethysmography) and oxygen pressure was measured in the gastrocnemius muscles (by micro-Pt-electrodes) of the anesthetized animals. 4 to 6 weeks after the operation statistically significant differences between the two extremities were noted: In the operated leg the meanpO₂-value was 33% lower (P<0.001) and the mean blood flow value 46% higher (P<0.001). These differences could be explained by a reduced number of perfused capillaries in the untrained muscles (=non uniform blood flow distribution).     

Forearm vascular responses to combined muscle metaboreceptor activation in the upper and lower limbs in humans

Our previous studies showed that venous occlusion or passive stretch of the lower limb, assuming a mechanical stimulus, attenuates the vasoconstriction in the non-exercised forearm during postexercise muscle ischaemia (PEMI) of the upper limb. In this study, we investigated whether a metabolic stimulus to the lower limb induces a similar response. Eight subjects performed a 2 min static handgrip exercise at 30% maximal voluntary contraction (MVC) followed by 3 min PEMI of the upper limb, concomitant with or without 2 min static ankle dorsiflexion at 30% MVC followed by 2 min PEMI of the lower limb. During PEMI of the upper limb alone, forearm blood flow (FBF) and forearm vascular conductance (FVC) in the non-exercised arm decreased significantly, whereas during combined PEMI of the upper and lower limbs, the decreases in FBF and FVC produced by PEMI of the upper limb was attenuated. Forearm blood flow and FVC were significantly greater during combined PEMI of the upper and lower limbs than during PEMI of the upper limb alone. When PEMI of the lower limb was released after combined PEMI of the upper and lower limbs (only PEMI of the upper limb was maintained continuously), the attenuated decreases in FBF and FVC observed during combined PEMI of the upper and lower limbs was not observed. Thus, forearm vascular responses differ when muscle metaboreceptors are activated in the upper limb and when there is combined activation of muscle metaboreceptors in both the upper and lower limbs.     

Activity of acid hydrolases in skeletal muscle of untrained,trained and detrained mice of different ages

The activities of p-nitrophenylphosphatase, β-glucuronidase and β-N-acetylglucosaminidase from crude skeletal muscle homogenates of 4 and 7 months old mice were assayed after short-term intensive and long-term moderate training and after terminated training. In the older untrained mice the activity of the hydrolases was higher than in the younger mice. The level increased with training and this increase was far more pronounced in the older animals. Cessation of training for 7 and 21 days decreased this activity in the older animals but it was again increased 42 days later and cIose to the level observed in the trained mice. In young mice 3 days' terminated training increased the activity of the acid hydrolases above the level of the trained animals but after additional 4 and 11 days' terminated training the activity decreased to slightly below that of the trained mice. The changes were most prominent in the activity of β-glucuronidase and to a lesser extent in that of β-N-acetylglucosaminidase while p-nitrophenylphosphatase activity was almost unaffected by training or terminated training. The effects of terminated training can he intepreted as representing altered catabolic processes in the turn-over of tissue components of skeletal muscle.     

Diurnal variations of serum erythropoietin in trained and untrained subjects

The diurnal variations of serum-erythropoietin concentration ([s-EPO]) were investigated in six physically trained (T) and eight untrained (UT) men. The T subjects had a higher mean maximal oxygen uptake than UT subjects [75.7 (SEM 1.6) ml · min^–1 · kg^–1 versus 48.3 (SEM 1.4) ml · min^–1 · kg^–1, P < 0.0001] and a lower mean body mass index [BMI, 21.7 (SEM 0.7) kg · m^–2 versus 24.4 (SEM 0.6) kg · m^–2, P=0.02]. Each subject was followed individually for 24 h as they performed their normal daily activities. Venous blood samples were collected from awakening (0 min) until the end of the 24-h period (1440 min). Both T and UT had a nadir of [s-EPO] 120 min after awakening [10.0 (SEM 0.3) U · 1^–1 versus 11.5 (SEM 2.1) U · 1^–1, P > 0.05]. The UT and T increased their [s-EPO] to peak values at 960 min and 960–1200 min, respectively (ANOVA P=0.03) after awakening [UT: 18.4 (SEM 2.8) U · l^–1; T: 16.2 (SEM 2.5) U · l^–1, P > 0.05]. The mean 24-h [s-EPO] were 14.5 (SEM 1.0) U · l^–1 and 14.9 (SEM 0.9) U · l^–1 in T and UT, respectively (P > 0.05). The individual mean 24-h [s-EPO] were not correlated to body mass, BMI or maximal oxygen uptaken. Significant diurnal variations in [s-EPO] occurred in these healthy subjects irrespective of their levels of physical activity.