Chapter 1
Energy demands of volleyball
Ronald J. Maughan and Susan M. Shirreffs
School of Medicine, University of St Andrews, St Andrews, Scotland
Introduction
Volleyball, like all team sports, requires repetitive bouts of high‐intensity exercise. For the volleyball player to achieve competitive success, he/she must possess the ability to rapidly generate power while executing precise sport‐specific skills such as spiking and blocking. In addition, the ability to maintain sufficient power output for the full duration of matches is obviously of critical importance to sporting success. The extent and speed of recovery from exercise are influenced by the intensity and duration of the preceding bout of exercise, the nutritional status of the individual, and the time available for metabolic recovery. Volleyball athletes must perform numerous maximum effort jumps and quick, short sprints, interspersed by variable periods of exercise of lower intensity or brief periods of rest. The energy used during periods of high‐intensity play is derived largely from anaerobic metabolism. Over the course of the match, however, the contribution of aerobic metabolism increases to cover the total energy cost. The cycles of activity and rest are imposed by the pattern of play which vary greatly from player to player and from one match to another, as the tactics and ability of the opposition also influence the demands on each player.
Compared with continuous exercise activities such as running and cycling, relatively little attention has been directed to the energy expenditure during games that involve complex movement patterns. This may be because of the lack of adequate experimental models to study these activities in the laboratory. However, some standardized models of intermittent exercise have been developed recently that simulate the activity patterns observed in team sport. This chapter describes how these protocols, as well as measurements made during competition itself, have shed some light on the metabolic processes that occur during match‐play exercise and their importance for achieving peak performance.
Activity patterns and work rate in volleyball and other sports
Based upon unpublished data collected by the Fédération Internationale de Volleyball (FIVB) during the 2015 World League and Grand Prix competitions, it appears that the work periods for elite male indoor players range between 6–8 seconds in length, while for elite female indoor players the work periods typically measure 7–9 seconds. Furthermore, the ball is “in play” for approximately 15% of the duration of the match, resulting in a work:rest ratio of approximately 1:6. These data reflect the fact that volleyball athletes must generate explosive power, then recover quickly so as to be ready for the next point.
It is predictable that players suffer from progressive fatigue as the competitive match wears on, as manifested by a drop in the work rate during the second half of the match (fewer number or reduced height of maximum jumps performed). A recent study of professional soccer players using Pro‐Zone technology to analyze time spent in different activities during 28 English Premier League matches found that during the last 15 minutes of a match, athletes cover approximately 20% less distance than they had covered during the opening of the match. There was also a noticeable decline in high‐intensity running immediately after the most intense 5‐minute period of the game, with the greatest deficits (~40–50%) in attacking players and central defenders. It is common to see more goals scored in the later stages of games as players become fatigued and more mistakes are made. Injuries are also more likely to occur late in the game when fatigue becomes more prevalent.
The development of fatigue during match‐play seems to be related at least in part to depletion of muscle glycogen stores. It has been shown that football players who start a match with a low thigh muscle glycogen content cover 25% less distance than those who have normal prematch thigh muscle glycogen stores (see Table 1.1). Furthermore, players with a low initial muscle glycogen content covered 50% of the total distance walking and only 15% sprinting, compared with 27% walking and 24% sprinting for the players with normal to high muscle glycogen stores. Blood lactate concentration is consistently lower at the end of a match compared with values measured at half‐time, and this ties in with the observation that the greatest rate of decline in muscle glycogen occurs in the first half of the match. Players who start matches with low glycogen stores in their leg muscles are likely to be close to complete glycogen depletion by half‐time and these findings have important implications for training and the nutritional preparation of players. Until relatively recently, however, these issues have largely been ignored.
Table 1.1 Maximum rates of ATP resynthesis that can be achieved by the metabolic pathways available to muscle cells.
ATP, adenosine triphosphate; CHO, carbodhydrate; PCr, phosphocreatine.
Metabolic responses to intermittent high‐intensity exercise
All cellular activities, including nerve transmission, biosynthesis, and muscle contractility, are fueled by the chemical energy released when the high‐energy phosphate bond(s) in the adenosine triphosphate (ATP) molecule are broken (Figure 1.1). ATP is broken down under the influence of a specific enzyme (an ATPase) to adenosine diphosphate (ADP) and inorganic phosphate (Pi) to yield energy for muscle activity or to power other reactions. This high‐energy phosphate bond is an immediate source of energy, the so‐called energy currency of the cell. All other energy‐producing reactions must channel their output through this mechanism.
Figure 1.1 Energy is released to allow cells to do work when the ATP molecule is hydrolyzed to ADP and Pi. The ATP level in the cells must be maintained to allow work to continue, so other metabolic pathways must provide the energy for ATP resynthesis.
There are three principal means by which cells maintain their supply of readily available ATP. The first and most rapid of the routes begins with the conversion of phosphocreatine (PCr) to creatine and phosphate. However, the phosphate group is not liberated as inorganic phosphate, but is rather transferred directly to an ADP molecule to re‐form ATP. This reaction is catalyzed by the enzyme creatine kinase, which is present in skeletal muscle at very high activities, allowing the reaction to occur rapidly. In the second pathway, glucose‐6‐phosphate (derived from the breakdown of muscle glycogen or from glucose taken up from the bloodstream) is metabolized to lactate and produces ATP by substrate‐level phosphorylation reactions. Neither of these reactions requires oxygen, and the pathways are therefore commonly considered to be “anaerobic.”
In the third pathway, the products of carbohydrate, lipid, protein, and alcohol metabolism can enter the tricarboxylic acid (TCA) cycle (also known as the citric acid or Krebs cycle, after Sir Hans Krebs, who first described it) in the mitochondria and can be oxidized to carbon dioxide and water. This process is known as oxidative phosphorylation, and in the presence of oxygen yields substantial energy used in the synthesis of ATP.
Adenosine triphosphate, then, is the immediate source of cellular energy and the purpose of the three mechanisms described is to regenerate ATP at sufficient rates to prevent a significant decline in the intramuscular ATP concentration. If the ATP concentration falls, the concentrations of ADP and adenosine monophosphate (AMP) will rise. The concentration ratio of ATP to ADP and AMP is a marker for the energy status of the cell. If the ratio is high, the cell is in effect “fully charged.” This energy charge is monitored in every cell; a fall in the ATP concentration or a rise in the concentration of ADP or AMP will activate the metabolic pathways necessary to increase ATP production. This is achieved by activation or inhibition of key regulatory enzymes by changes in the concentration of the adenine nucleotides.
It may also be helpful to think of the various pathways that can be used to resynthesize ATP in terms of the maximum rates of resynthesis that can be achieved. Some typical values are shown in Table 1.1. It is important to note that these rates are influenced by many factors, including muscle fiber type, fitness level, and the nutritional status of the athlete.
Since substantial storage of ATP in tissues is not possible (the amount of chemical energy stored in each molecule of ATP is rather small and it would be inefficient to store more because of the mass that would have to be carried), the challenge during exercise is for the cell to resynthesize ATP as fast as it is broken down, thereby maintaining an adequate intracellular supply of energy. A 70 kg runner moving at a speed of 15 km/h will require about 3.5 L of oxygen per minute, or about 1.17 kW. To meet this energy demand, the runner must...
