What are the physiological effects of exercise?
Exercise causes a reduction in the muscle glycogen stores. Strenuous exercise will also result in muscle tissue damage. This damage is due, in part, to the physical stress placed on the muscle, particularly during the eccentric phase of muscle contraction (Clarkson & Hubal, 2002), and hormonal changes that result in the breakdown of muscle protein, as well as fat and carbohydrate, to provide the fuel for powering muscle contraction (Walsh et al., 1998). However, muscle damage does not just occur during exercise, but can continue after exercise for many hours. This occurs as a result of a protracted exercise hormonal milieu, an increase in free radicals and acute inflammation. Not only will such tissue damage limit performance due to delayed onset muscle soreness, but it will also compromise the replenishment of muscle glycogen and limit muscle training adaptations (Costill et al., 1990).
Carbohydrate availability/storage within the body:
Muscle glycogen represents the major source of carbohydrate in the body (300 to 400g, or 1200 to 1600 kcal), followed by liver glycogen (75 to 100g or 300 to 400 kcal) and, lastly, blood glucose (25g or 100 kcals). These amounts vary widely between individuals, depending on factors such as dietary intake and state of training. Untrained individuals have muscle glycogen stores that are roughly 80 to 90 mmoL/kg of wet muscle weight. Endurance athletes have muscle glycogen stores of 130 to 135 mmoL/kg of wet muscle weight. Carbohydrate-loading can increase muscle glycogen stores to 210 to 230 mmoL/kg of wet muscle weight (Jacobs & Sherman, 1999).
Fat availability/storage within the body
Triglycerides in adipocytes stored throughout the body represent the major source of fats in the body (5600g-6600g or 50,000 to 60,000 kcals of energy) (Manore & Thompson, 2000). Fat can also be stored as “droplets” within skeletal muscle cells. These fat droplets are called intramuscular triglycerides (IMTG) and they may hold 220g-330g or 2,000 to 3,000 kcals of stored energy (Manore & Thompson, 2000). In addition to the stores of fat, some triglycerides travel freely in the blood. During exercise, triglycerides in fat cells, muscle cells, and in the blood can be broken down and used as fuel by the exercising muscles.
What happens to carbohydrates during exercise?
Exercise results in loss of carbohydrates stored as glycogen in muscles and the liver. Glucose is oxidized by cells to produce energy for working muscles. After an hour of hard exercise, the loss contributes to the feeling of fatigue, and a decline in performance. This occurs because the brain is affected by a fall in blood glucose concentration and the depletion of glycogen stored in muscle reduces the ability of muscle contractions (Hopkins & Wood, 2006).
What are the benefits of carbohydrate feeding during exercise?
It has been shown that carbohydrate feeding during exercise “spares” liver glycogen. Hepatic glucose output is tightly regulated, ensuring a relatively constant glucose output in the presence or absence of carbohydrate feeding. Although the total rate of appearance of glucose increases somewhat with increasing rates of carbohydrate intake, there is a progressive decrease in endogenous glucose production (liver glycogenolysis and gluconeogenesis) with increasing rates of carbohydrate intake. This liver glycogen sparing means that there are still carbohydrates in the liver toward the end of exercise, which could be beneficial if, for whatever reason, carbohydrate intake cannot supply enough carbohydrates to maintain plasma glucose concentrations and high rates of total carbohydrate oxidation (Jeukendrup et al., 1999). Carbohydrate feeding during exercise improves endurance performance by maintaining blood glucose and high levels of carbohydrate oxidation, sparing endogenous glycogen and synthesizing glycogen (Jeukendrup, 2004). A better maintenance of blood glucose can be used by the exercising muscles with a consequent reduction in the need for mobilisation of the limited liver glycogen reserves (McConnell et al., 1994).
What is oxidation efficiency?
Oxidation efficiency refers to the percentage of the ingested carbohydrate that is oxidized. High oxidation efficiency means that smaller amounts of carbohydrates remain in the gastrointestinal tract, and this will reduce the risk of developing gastrointestinal complaints during prolonged exercise. The oxidation efficiency of drinks containing carbohydrates that use different transporters for intestinal absorption (glucose & fructose) is higher than that of drinks with a single carbohydrate (Brouns & Beckers, 1993).
What is osmolarity and why is it important in a sports drink?
Osmolarity is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L) (the number of particles in the solution). The osmolality of a sports drink can influence the rate of gastric emptying and intestinal water flux. Hypotonic solutions promote gastric emptying and water absorption from the proximal small intestine (Maughan, 1998), whereas hypertonic solutions slow gastric emptying and fluid absorption, and promote the occurrence of exercise-related abdominal pain (stitch) (Morton et al., 2004).
Water absorption occurs largely in the proximal segment of the small intestine, and although water movement is itself a passive process driven by local osmotic gradients, it is closely linked to the active transport of solute. Osmolality plays a key role in the flux of water across the upper part of the small intestine. Net flux is determined largely by the osmotic gradient between the luminal contents and intracellular fluid of the cells lining the intestine (Gisolfi et al., 1990).
What are the effects of water and sodium depletion during exercise?
Exercise results in loss of water and sodium from the body via evaporation of water from the lungs and sweating of water and sodium from the skin. For exercise of sufficient duration and intensity, the losses reduce the volume of blood available for the heart to pump to the muscles and skin. Reduction of blood flow to muscles implies less delivery of oxygen to the muscles, so endurance performance declines. Reduction of blood flow to the skin implies less elimination of heat from the body, so the risk of heat stroke (damage to cells and tissues from overheating) increases, especially in a hot or humid environment. The loss of water and sodium may also reduce production of sweat, which will also increase the risk of heat stroke. These effects become substantial for near-maximal exercise lasting an hour in a hot humid environment and two hours in a cool environment (Hopkins & Wood, 2006).
What are the effects of dehydration?
There is a general consensus in the literature that dehydration should not exceed 2% of body weight loss during most athletic events (Noakes & Martin, 2002). Dehydration reduces heat dissipation by reducing skin blood flow during exercise, usually resulting in an increased body core temperature (Gonzalez-Alonso et al., 1995). Dehydration also induces cardiovascular strain during exercise, best evidenced by a reduction in stroke volume. Using this reduced stroke volume as a reflection of cardiovascular strain during exercise, Gonzalez-Alonso (1998) has reported that dehydration without hyperthermia reduces stroke volume by 7–8% and that hyperthermia without dehydration also reduces stroke volume by 7–8%. However, the combination of dehydration and hyperthermia elicits synergistic effects in reducing stroke volume by more than 20%. Overall reducing cardiac output and increasing systemic and cutaneous vascular resistance during exercise which results in reduced performance.
How much fluids do runners consume?
Runners generally consume less than 500 ml of fluid per hour (Noakes et al., 1991). This is because of the difficulty of drinking on the run and the potential discomfort of running with a full stomach. Therefore, runners tend to use more concentrated solutions (8-10%, double strength) of carbohydrate or consume energy gels to minimise gastrointestinal disturbances.
Is water sufficient for exercise less then 2 hours?
In the ACSM position statement on ‘Exercise and Fluid Replacement’, it was concluded that ‘During intense exercise lasting longer than 1 hour, it is recommended that carbohydrates be ingested at a rate of 30–60 g/h to maintain oxidation of carbohydrates and delay fatigue’.
What are the factors that effect gastric emptying?
Fluids which contain a high concentration of particle in solution (osmolality) can reduce gastric emptying. The rate the stomach empties greatly affects intestinal absorption of fluid and nutrients. Little negative effect of exercise on gastric emptying occurs up to an intensity of about 75% of maximum, after which emptying rate slows (Schedl et al., 1994). Gastric volume, however, greatly influences gastric emptying; the emptying rate increases exponentially as fluid volume in the stomach increases. A major factor to speed gastric emptying involves keeping a relatively high fluid volume in the stomach. Consuming 150-250 ml of fluid immediately before exercise optimizes the beneficial effect of increased stomach volume on fluid and nutrient passage into the intestine. Research has also indicated that colder fluid empty from the stomach at a faster rate than fluid at room temperature (McArdle et al., 2007).
How many Calories do you burn during exercise?
Exercising for 1 hour at approximately 70% VO2max requires approximately 1,000 kcal for a male and 600-700 kcal for a female (Tarnoplosky et al., 2005).
How to utilise carbohydrate-loading prior to competition?
The current method of ‘carbohydrate-loading’ during the week prior to competition is to gradually reduce the volume of training throughout the week and to increase the carbohydrate intake to about 600 g/day during the last 4 days before the event (Bangsbo et al., 1992). Muscle glycogen concentration is increased above normal resting values as a consequence of this dietary preparation for competition. However, the recommended amount of carbohydrates may not be appropriate for female athletes because, for many, it would be equivalent to their daily energy intake (approximately 10 MJ (2400 kcal)). Therefore, it is more appropriate that daily carbohydrate intake in terms of g/kgbw. Expressed in this way the recommendation for carbohydrate loading is a daily intake of 9 to 10g/kgbw of carbohydrate during the days immediately preceding competition (Nicholas et al., 1997).
What are the benefits of sodium phosphate?
Sodium phosphate has a potential ergogenic value. A number of studies indicated that sodium phosphate can increase maximal oxygen uptake (i.e., maximal aerobic capacity) and anaerobic threshold. These findings suggest that sodium phosphate may be highly effective in improving endurance exercise capacity (Kreider et al., 1992).
Do sports drinks have an effect on dental health?
Athletes consume sports drinks on a daily basis and the ingested amount can easily reach more than 3L per day. Since sports drinks are usually ingested a sip at a time, the drinks’ residue remains in the oral cavity for quite some time. This can influence tooth health because the drink may have a high titratable acid or low pH value, which in turn is related to dental erosion (Meurman et al., 1990 & Venables et al., 2005). Pro4mance Sports Nutrition products are specifically formulated with dental health in mind. They have minimal levels of citric acid which minimised titratable acid levels and contain buffers which prevent low pH levels.
Which electrolytes are found in sweat?
The average concentrations of electrolytes within sweat are: sodium, 10mmol/L (range 5-20mmol/L); potassium, 5mmol/L (range 3-15mmol/L); magnesium, 0.8 mmol/L (range 0.2–1.5 mmol/L) and calcium, 1 mmol/L (range 0.3–2.0 mmol/L) (Criswell et al., 1992; Cunningham, 1997; McCutcheon & Geor, 1998; Sawka & Montain, 2000).
How are free fatty acids (FFA) mobilized from adipose tissue?
The large stores of triglyceride within adipose tissue are mobilised at relatively slow rates during exercise. In this process, exercise stimulates an enzyme, hormone sensitive lipase, to dissolve the lipid or triglyceride molecule into three molecules of unbound or free fatty acids (FFA) and one glycerol molecule. This process of breaking down triglycerides is known as lipolysis (Coyle, 1995).The fate of the three FFA molecules released from adipose tissue during lipolysis is complex. These fatty acids are not water soluble and thus require a protein carrier to allow them to be transported through cells and within the blood stream (Coyle, 1995). At rest, about 70% of the FFA released during lipolysis are reattached to glycerol molecules to form new triglycerides within the adipocytes. However, during low-intensity exercise, this process is attenuated at the same time as the overall rate of lipolysis increases; as a result, the rate of appearance of FFA in the plasma increases by up to five fold (Klein et al., 1994). Once they enter the plasma, the FFA molecules are loosely bound to albumin, a plasma protein, and transported in the circulation. Some of the fatty acids are eventually released from albumin and bound to intramuscular proteins, which in turn transport the FFA to the mitochondria for oxidation (Turcotte et al., 1991).
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