P. D. Gollnick

Exercise intensity, training, diet, and lactate concentration in muscle and blood.

With some, but not all, types and intensities of exercise, lactate accumulates in the blood and in the muscles engaged in the exercise. A great deal of attention has been directed towards attempting to understand the dynamics of lactate production and removal at the onset of exercise, during exercise, and during the recovery process following exercise. It has been hoped that an unravelling of these events would provide a key to understanding cellular metabolism and its regulation during exercise. The purpose of this introductory paper to a symposium on lactate is to present a brief overview of some of the conditions that influence the rate and magnitude of lactate accumulation during exercise. It is pointed out that many conditions influence the rate and magnitude of the accumulation of lactate in blood and muscles. Included are diet, state of physical fitness, and the type and duration of the exercise. We have cautioned against trying to evaluate the state of oxygen delivery to muscle and the state of tissue oxygenation from the appearance of lactate in blood. We have pointed out the positive aspects of lactate production based on how it augments the cellular supply of ATP, thereby allowing for high intensity exercise, and also the negative aspects that develop as a result the reduction in pH which adversely influences many cellular processes essential for muscular activity.

Oxygen uptake of rats at different work intensities

SummaryAn adaptation of a standard activity wheel has been used to determine oxygen uptake of rats prior to and during exercise at 7 different speeds (16–67 m/min). Pre-exercise oxygen uptake was 2.42±0.10 (S.E.) ml (100 g×min)−1 Oxygen uptake increased linearly with work intensity (running speed). At 16 m/min oxygen uptake was 6.44±0.16 ml (100 g×min)−1 and it increased to a maximal value of 9.51±0.14 ml (100 g×min)−1 at a running speed of 53.6 m/min. Increasing running speed to 67 m/min did not produce any further increas in oxygen uptake. Some comparisons of exercise intensity between rats of various studies and rats and man can be made from these data.

Glycogen depletion in rat skeletal muscle fibers at different intensities and durations of excercise

SummaryTotal muscle glycogen depletion, the glycogen depletion pattern (PAS staining) in the different fiber types of skeletal muscle, and several other measures of carbohydrate metabolism were studied in rats that ran 162.2 m at varying speeds (22.5–80.5 m/min) or swam from 0.5–4 hrs. Muscle glycogen declined as an increasing function of exercise intensity during running whereas during swimming there was a near linear decline in muscle glycogen throughout the 4 hrs of exercise. Blood lactate did not increase until running speed exceeded a load that would required a VO2 of about 60% of aerobic capacity. a peak lactate of 21.15 mM occurred after the rats ran at 67m/min. Liver glycogen declined steadily at a rate of about 0.6 mg×g−1×min−1 during the first 2 hrs of swimming. During this time blood glucose was maintained at or above resting levels. During the final 2 hrs of swimming glycogenolysis in the liver declined to about 0.09 mg×g−1×min−1 and there was then a sharp decrease in blood glucose to a final value of 68.7 mg/100 ml. At low running speeds and during the first hour of swimming the greatest loss in PAS staining occured in fast-twitch-oxidative-glycolytic (FOG) and slow-twitch-oxidative (SO) fibers. At running speeds above about 50 m/min a rapid loss of PAS staining was observed in the fast-twitch-glycolytic (FG) fibers. These higher speeds are above those that should elicit VO2 max for the rat. In the late stages of swimming FG fibers also demonstrated a loss of glycogen. These data suggest that at low work intensities there is a primary reliance upon oxidative fibers for contractile activity and that a major use of anaerobic fibers only occurs at high work levels or when the aerobic fibers are depleted of glycogen during prolonged-low intensity work.

Differentiation of fiber types in skeletal muscle from the sequential inactivation of myofibrillar actomyosin ATPase during acid preincubation

SummaryA method is described for identifying fiber types of skeletal muscle from several mammalian species on the basis of the sequential inactivation of myofibrillar actomyosin ATPase during acid preincubation. When this method is used in combination with the standard alkaline preincubation at least 5 types of fibers can be identified. Of these, 2 are type I fibers with those of the slow twitch soleus muscle being different from those that exist in mixed muscles. The 3 subtypes of type II fibers exist independent of their metabolic properties. The need for careful standardization of histochemical methods for the visualization of myofibrillar actomyosin ATPase and the implication of the existence of different fiber types in apparently homogeneous muscle for the preparation of antibodies used for immunocytochemical methods of fiber identification are discussed.

The effect of high-intensity exercise on the respiratory capacity of sceletal muscle

The effect of high-intensity exercise on the respiratory capacity of skeletal muscle was studied in horses which ran five 600-m bouts on a track with 2 min of rest between exercise bouts, or once to fatigue on a treadmill at an intensity that elicited the maximal oxygen uptake. Venous blood and biopsy samples of the middle gluteal muscle were collected at rest, after each exercise bout, and 30 and 60 min post-exercise. Blood samples were analyzed for lactate concentration and pH and muscle samples for metabolites, pH, and respiratory capacity. Venous blood and muscle pH declined to 6.91±0.02 and 6.57±0.02, respectively, after the fifth track run and to 6.98±0.02 and 6.71±0.07, respectively, after treadmill running. Muscle metabolite changes were consistent with the metabolic response to high-intensity exercise. Muscle respiratory capacity declined >20% (P<0.05) after a single exercise bout and was 45% of the control value after the fifth track run. Tissue respiration was depressed 60 min post-exercise but was normal 24 h later. These observations suggest that high-intensity exercise impairs the respiratory capacity of the working muscle. Although this occurred in parallel with reductions in pH, other factors could be responsible for this response.

Respiratory and metabolic responses in the horse during moderate and heavy exercise

Thoroughbred horses were exercised to fatigue on a treadmill at 62% and 100% of their VO2max. Hypoxemia occurred at the onset of exercise under both exercise conditions. This hypoxemia persisted to fatigue during the heavy exercise but progressively diminished as the exercise continued and had disappeared by the end of exercise at the lighter load. As a result of the hypoxemia the oxygen content of arterial blood during exercise at VO2max was 17% below its carrying capacity. However, under both experimental conditions the CaO2 still exceeded that of rest owing to an elevation in hemoglobin concentration. The temperature of blood at the point of fatigue was similar, 41.0±0.2 ° C and 41.1±0.2 ° C, for exercise at 62% and 100% VO2max, respectively. Muscle samples collected at rest and at the termination of exercise did not demonstrate major differences between the exercise conditions except for a higher [lactate] and lower pH following the heavy exercise. From these results it can be suggested that the combined effects of an elevated body temperature, changes in muscle pH, and oxygen delivery may all be factors contributing to limit exercise capacity in the horse.

The muscle fiber composition of skeletal muscle as a predictor of athletic success An overview

Human skeletal muscle is composed of varying percentages of fiber types. This percent composition varies widely between muscles and among individuals. The fiber composition of some skeletal muscle could be construed as being advantageous to successful performance in selected athletic event. However, this relationship is not sufficiently close to warrant the conclusion that the fiber composition of the muscle per se is the determinant of the superior performance of elite athletes. Reasonably good evidence exists to support the position that the fiber composition of a muscle is the result of a genetic endowment. Although muscle fibers are mutable, present evidence is equivocal as to whether habitual participation in given type of physical activity is responsible for high percentages of a given fiber type being present in the muscles of some athletes. Although considerable knowledge has come from the study of muscle samples obtained from sedentary individuals, athletes of a wide range of performance capacity, and individuals before and after training, a considerable gap remains for a full understanding of how the characteristics of muscle are related to performance capacity. The observation that considerable variation exists in the percent distribution of the fibers within a muscle and that athletes with a wide range of fiber populations in their muscles can be successful in the same athletic event cautions against the routine application of the biopsy technique to estimate the fiber distribution of muscles and also to use such data as a routine screening procedure for predicting athletic success. The point, as was made in an earlier paper, that the biopsy technique for studying muscle is a research tool, will probably continue to be true for the near future.

Response of ventilatory muscles of the rat to endurance training.

The effect of endurance training on the oxidative and glycolytic potentials of the diaphragm and intercostal muscles of rats has been studied. Training consisted of treadmill running (28 m/min, 60 min/day, 5 days/wk) for periods ranging from 8–26 weeks. Exercise of similar duration and intensity produced a glycogen depletion in the diaphragm and intercostal muscles of nontrained rats. Oxidative potential was estimated from the activity of the mitochondrial marker enzyme succinate dehydrogenase (SDH). The activities of phosphorylase (PHOS), hexokinase (HK), and lactate dehydrogenase (LDH) were determined as well as the distribution of the LDH isozymes. SDH activity averaged 44 (42–51) and 17 (10–22)% (P<0.01) greater in the plantaris and diaphragm muscles, respectively, after 8–12 weeks of endurance running as compared to the sedentary animals. There was no change in the SDH activity of the intercostal muscles or in the activities of the glycolytic enzymes. There was also no change in the distribution of the isozymes of LDH. Extending the duration of the training program to 26 weeks did not produce any additional alteration in the magnitude of the adaptation observed after the initial training period. Comparative studies of different types of muscles demonstrated that the diaphragm, although having a fiber composition somewhat similar to that of a fast-twitch skeletal muscle, has a metabolic profile that is intermediate between pure slow twitch skeletal muscle and cardiac muscle.

Response of Skeletal Muscle to Training

SummaryPhysical training induces adaptive changes in skeletal muscle. These changes are localised to the active muscle with their magnitude depending upon the nature, i.e. time and intensity, of the training regimen. The most notable changes are increased concen-trations of mitochondria and glycogen.With endurance training there are major changes in metabolism in that there is a greater contribution of fat to the total metabolism during submaximal exercise. This re-sults in a conservation of the stores of glycogen with the net result of increasing total exercise capacity. This increased use of fat during submaximal exercise appears to be more closely related to the elevations in the concentration of mitochondria in muscle than to changes in total body maximal oxygen uptake. The combination of a greater contri-bution of fat to the metabolism and the elevated concentration of stored glycogen are prime factors contributing to the enhanced endurance capacity after endurance training.The mechanism for the greater use of fat after endurance training is discussed. Evi-dence now supports the hypothesis that this is due to a tighter control over the Embden-Meyerhof pathway as a result of the greater concentration of mitochondria. The effect of heavy resistance exercise on the size and strength of skeletal muscle is discussed. Some attention is focused on the recently revived controversy concerning whether muscle en-largement is the result of a hypertrophy of pre-existing fibres or of hyperplasia. It is con-cluded that although there is considerable evidence to support the development of hyper-trophy in response to heavy resistance exercise, the contention that a splitting of fibres occurs to produce a greater fibre number is presently poorly supported.

Anaerobic enzyme adaptations to sprint training in rats

SummaryThe adaptability of several regulatory glycolytic enzymes to chronic sprint exercise has been investigated. Ten animals were subjected to an 11-week running program consisting of 30-sec sprints interposed with 30-sec rest periods and were running up to 18 sprints a day at 80.5 m/min during the eleventh week. Ten animals served as sedentary controls. Phosphorylase (PHOS), phosphofructokinase (PFK), and pyruvate kinase (PK) activities were estimated in samples from the red and white portions of the gastrocnemius muscle (RG and WG), the red area of the vastus lateralis muscle (RV), and the soleus muscle (S). In control animals the activities of PHOS, PFK, and PK were highest in the WG, followed in order by the RV, RG, and S. Significantly more fast-twitch fibers were classified as high-oxidative in the WG of the trained animals. Only the S showed a consistent increase in glycolytic enzyme capacity with training. The findings indicate that most skeletal muscles possess sufficient anaerobic capacity to meet the demands of heavy, short-term intermittent work without adaptation to a higher level.