Endurance is defined as “the act, quality or power of withstanding hardship or stress”. Due to significant differences in fitness levels and other variables amongst individuals, an “endurance” event can mean very different things to different people. Here, “endurance activities” are any exercise or event that exceeds 60-90 minutes. This is commonly the period of time at which an individual requires additional nutrition to continue to function optimally.
Endurance activities place increased nutritional and hydration demands on the body. There are often higher requirements for water, macronutrients (e.g. carbohydrate and protein), micronutrients (e.g. minerals) and electrolytes both throughout training and on a day to day basis if such activities are carried out regularly.
Dehydration, hyperthermia (over-heating) and a depletion of muscle glycogen are major contributors to reduced performance during prolonged exercise.1
Healthy hydration throughout exercise is important to avoid thermal/heat stress, impaired cognitive function, accelerated fatigue and impaired exercise performance. Water is often substantial for activities lasting <75 minutes (with exceptions such as high intensity sport performed in high heat). Outside of this, carbohydrate and electrolyte replacement have been shown to assist in maintaining performance and speeding recovery (i.e. supporting rapid refuelling of muscle glycogen and reduced muscle soreness etc).
Carbohydrate is a key fuel source for exercise, especially during prolonged continuous or high intensity exercise. The body stores carbohydrate as glycogen in the muscles and liver, however its storage capacity is limited. When carbohydrate stores are inadequate to meet the fuel needs of a workout this results in fatigue, impaired performance, reduced concentration and even reduced immune function when carbohydrate depletion is ongoing.2
During prolonged exercise, ingesting carbohydrate can prevent drops in blood glucose concentration and may help to maintain high rates of carbohydrate oxidation which is needed to maintain high intensity exercise. Many athletes have difficulty with consuming food before or during exercise and therefore a formulated drink that will provide carbohydrate is helpful. Maltodextrin is a useful carbohydrate option as it dissolves in water and is rapidly broken down to glucose for absorption.
Recent findings have confirmed the benefit of combined consumption of protein and carbohydrate during exercise. In one study this combination, when consumed during strenuous training, suppressed exercise stress as indicated by reduced heart rate, lower rating of perceived exertion (RPE) and less muscle damage. This was compared to carbohydrate intake alone.The study also suggested that taking a protein and carbohydrate combination during training can enhance recovery, with subjects demonstrating a worthwhile improvement in a subsequent cycling time-trial performance.3
Moreso, during the second hour of exercise the body gets 5-15% of its energy from amino acids. If no amino acids are supplied, the body will scavenge amino acids from muscle tissue. It is therefore worthwhile to supplement with protein that provides readily available amino acids during endurance-type events or exercise that lasts longer than one hour.
A protein that is easily digested and assimilated is ideal for consumption during exercise as it reduces the risk of stomach upset and ensures optimal uptake of beneficial amino acids. PeptoPro® is a peptide formulation derived from dairy protein. The milk protein in PeptoPro® has been pre-digested down to dipeptides and tripeptides, which are rapidly absorbed for faster delivery of amino acids to muscles. This protects the muscles during exercise and reduces muscle damage.
Salt (or sodium) is often the key mineral that comes to mind when many individuals think of replacing electrolytes due to losses through sweat. The truth is, sweat is comprised of many minerals or electrolytes including sodium plus potassium, magnesium, chloride and calcium. Each of these mineral have vital biochemical and physiological roles in the body and hence require replenishment both during and after an endurance event (or shorter training in high heat where sweat rate is high).
The electrolytes sodium, chloride and potassium contribute to systemic hydration via their essential role in maintenance of healthy cellular water distribution and acid-base balance in the body. Furthermore, sodium assists fluid retention prior to and during a sporting event, which can reduce the need for frequent urination.4 Magnesium, sodium and potassium provide nutritional support for healthy cardiovascular function and nerve conduction.
To help develop a fluid intake plan, both during and after exercise, athletes need to know about the magnitude of their sweat losses. The Australian Institute of Sport provides an easy formula for calculating Effective hydration strategies for sweat loss - http://www.ausport.gov.au/ais/nutrition/factsheets/hydration/how_much_do_athletes_sweat
Magnesium is one mineral that experiences significant losses during prolonged exercise and this depletion may be aggravated by mental stress during competition.5 Magnesium is involved in numerous processes that affect muscle function including oxygen uptake, energy production and overall electrolyte balance, further supporting the need for replenishment.
There is evidence that a mild depletion of magnesium impairs physical performance, recovery and can even amplify the negative consequences of strenuous exercise (e.g. oxidative stress).5
Magnesium is intrinsically involved in the healthy conduction of nerves, muscle contractions and normal rhythm of the heart. It supports healthy cellular energy production, storage and utilisation, assists in the metabolism of carbohydrates, plus may increase oxygen uptake capacity and reduce blood lactate levels. It also maintains proper muscle function, all attributes that contribute to magnesium’s ability to help maintain peak performance.
In terms of recovery, magnesium’s role in muscle relaxation makes it useful for the prevention and relief of muscular cramps and spasms and is beneficial during times of stress.
Coconut water supports hydration and is a naturally rich source of carbohydrate, protein, electrolytes (potassium, sodium, calcium and magnesium), other minerals (iron and phosphorous) and vitamins (vitamin C, B6, folate). Due to these properties it is viewed as the hydrating beverage of choice in certain parts of the world. Coconut water has been reported to have antioxidant properties, which may aid in neutralising free radical production that occurs during prolonged exercise.6
Medium chain triglycerides (MCTs) are different than long-chain fatty acids in the way they are absorbed and utilised in the body. Unlike other fats that delay gastric emptying, MCTs are quickly absorbed from the intestines and move to the liver to be utilised as an energy source, making them an ideal supplement during exercise. Further suggested MCT benefits include improved insulin sensitivity7 and enhanced absorption of minerals (calcium, magnesium) and amino acids.8 Results of studies have been conflicting, however, through their supply of energy, it is thought that MCTs may have a sparing effect on muscle glycogen after consumption.9
Osmolarity of sports drinks
When aiming to maximise the effectiveness of fluid and nutrient consumption, it is important to consider the osmolarity of the solution being ingested.
Put simply, the osmolarity of a solution refers to its concentration. An isotonic solution has an osmolarity that is equal to that of the blood. In contrast, a hypertonic solution is more concentrated than the blood, and hence hypotonic refers to a solution with a lesser concentration than blood.
The significance of this in sports hydration is in our understanding of osmosis. Fluid will move from a less concentrated environment to a more concentrated solution through a semi-permeable membrane (i.e. the gut wall). This means the fluid from an isotonic and hypotonic solution will move at ease from the gut into the blood, providing rapid hydration when compared to a hypertonic solution. Hypertonic solutions (e.g. fruit juice and soft drink) tend to stay within the digestive tract longer, delaying gastric emptying and increasing the risk of stomach upset. Isotonic and hypotonic solutions have been found to be the most effective means of hydration during training.
A solution providing 4% carbohydrate (in an isotonic dose) is an ideal means of providing a rapid delivery of fluid and fuel to maximise gastric tolerance (i.e. avoid stomach upset). To make a solution more hypotonic, simply add water.