D. R. Hodgson

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.

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.

The identification of fiber types in skeletal muscle: a continual dilemma

We have attempted to present an overview of some of the methods used for identifying and studying the fibers and motor units of skeletal muscle, and to give a short discourse on the particular strengths and weaknesses of these methods. It was not our intention to reach a final conclusion of there being only one way to identify muscle fibers or that the subject is closed to additional research. Quite the contrary, we intended to demonstrate that in the past two decades there has been an explosion of knowledge in this field. In the introduction, we suggested that the era of a simple classification scheme for categorizing fibers has passed. We also posed a number of questions. It seems that an appropriate conclusion would be to return to these questions with some answers. Our first question was what is the purpose of fiber typing? To us, its intent is to provide as much information as possible about fibers, accentuating their similarities and differences, such that the designated groupings are most meaningful. This has become increasingly difficult as the complex nature of skeletal muscle fibers has been unravelled and the diversity of those fibers previously thought to be similar is exposed. However, fiber typing schemes provide valuable information concerning the nature of the fibers and are important in attempting to describe the nature of muscle. Therefore, fiber typing is a necessary step in describing the complex characteristics of skeletal muscle. We also asked is more information needed? Clearly more information is needed to develop a complete understanding of the biochemical and functional aspects of muscle and how it adapts to a variety of experimental or naturally occurring perturbations. Thus, as time passes and more information is amassed, a constant revision of the schemes for identifying fibers can be expected. This is a positive sign of a viable field. A third question was is it worth trying to keep up or can one be expected to keep up with the seemingly rapid changes in the identification schemes used for fiber typing? This seems like an absurd question, and yet, it has been posed to us by university professors who are comfortable with and continue to use the old system(s) of muscle and fiber identification and who do not want to see things change. This question, when asked in any field, implies an unwillingness to make the effort to stay abreast with advancements occurring in that field.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Gas and Acid-Base Changes in the Neonatal Foal

This article reviews what are considered the basic concepts of gas transport, blood gases, and acid-base physiology is most mammalian species. Techniques for the appropriate collection of blood samples for blood gas and acid-base determinations in the newborn foal are described. Guidelines for interpretation of these values in the normal foal and those animals undergoing respiratory and metabolic derangements are provided.

Energy Considerations During Exercise

Maintenance of muscular contraction during exercise requires large amounts of chemical energy. Although various sources of energy are available, adenosine triphosphate (ATP) is the universal intracellular vehicle of chemical energy within skeletal muscle. This article will focus on the various mechanisms of the production and breakdown of ATP.

Muscular Adaptations to Exercise and Training

This article provides an overview of the characteristics of skeletal muscle, with an emphasis on equine skeletal muscle. A discussion of many of the adaptive processes that can occur in this tissue in response to altered states of physical activity is also included.