The science of human endurance


Endurance is the ability to sustain an activity for an extended period. A muscle’s ability to resist fatigue and sustain the contraction is measured in terms of the number of repetitions. Muscle endurance and strength together constitute muscular fitness. Improving muscle fitness makes difficult activities easier and decreases the risk of injury.

Resistance work enhances economy by eliminating wasted energy in excessive movement and by stabilising the running motion. Interval running, when done correctly, trains muscles to use oxygen more efficiently when working hard.

Endurance training programmes can produce small but measurable gains in muscular strength. Activities that require muscle endurance include sustained walking, running, cycling, resistance training, swimming, circuit training, aerobics, dance and rope jumping. In endurance training, the number of repetitions and the length of the muscle or group of muscles are more important than the resistance/load or intensity/speed at which the physical activity is performed.

Endurance athletes desire to maintain an optimal lean muscle that will complement and not hinder performance. Protein contributes only 1 to 6 per cent to total energy costs during endurance exercises, so it is not the main dietary focus. The primary sources of energy are fat and carbohydrates. The main goal of endurance training is to increase the anaerobic threshold as this improves training efficiency.

Improving performance

The three factors that affect endurance are:

1. The maximum capacity of a person to use oxygen during the exercise (VO2 max)

2. Running economy

3. Lactate (or anaerobic) threshold

VO2 max

Improving this can help the heart work more effectively, allowing more intense workouts and improving performance in events. It will also help the person call upon a wider range of speeds. VO2 max is largely genetically determined. Research has shown that whatever aerobic capacity an individual possesses can be improved with training by only about 25 per cent. Oxygen uptake in females is usually 65 to 75 per cent of those of males. VO2 max also declines with age.

Altitude training causes an increase in the haemoglobin content in the blood. So the altitude-trained people, when competing at sea level, seem to have enhanced aerobic performance.

Running economy

This is a physiological measure of the amount of oxygen required to run at a specific pace. The more economical the runner, the less oxygen will be needed to run at that pace. Improving running economy leads to lowered perceived effort at your current race pace, increased endurance at the current race pace, and the ability to run faster than the current competitive speed. Resistance work enhances economy by eliminating wasted energy in excessive movement and by stabilising the running motion. Interval running, when done correctly, trains muscles to use oxygen more efficiently when working hard.

The lactate threshold

This is the running speed at which large amounts of lactate begins to build up in the blood. Higher lactate levels cause pain in the muscles, which causes an athlete to reduce the level of exertion or slow down pace. An elevated lactate threshold helps the athlete run faster with less discomfort. It is a good indicator of performance in endurance events. The accumulation of lactate usually occurs at just below 10kmph pace. One should always stimulate a degree of lactate buildup to familiarise the muscles with lactate clearance capabilities. When training, it is important to take at least one week in four very easy, so as to allow the muscles to recover. Tempo running involves running a specified distance (four to six miles) at a pace just below the threshold. It is ideal for building endurance and generating lactate buildup.

Ultra-endurance sports

Ultra-endurance competition is defined as events that take six hours or more. These events rely on long-term preparation, sufficient nutrition, accommodation of environmental stressors, and psychological toughness. Successful ultra-endurance performance is characterised by sustaining a higher absolute speed for a given distance than other competitors. This can be achieved through a periodised training plan and by following key principles of training. Periodisation is an organisation of training into large, medium and small training blocks referred to as macro-, meso-, and micro-cycles. When the sequencing of training is correctly applied, athletes can achieve a high state of competition readiness and avoid the overtraining syndrome during the months of hard training. A plan is executed in accordance with the following principles of training—overall development, overload, specificity, individualisation, consistent activity and structural tolerance. The training relies heavily on the athlete’s tolerance to repetitive strain.

Today’s ultra-endurance athlete must also follow appropriate nutritional practices to recover and prepare for daily training and remain injury-free and healthy. Ultra-endurance events require energy contributions from all three macronutrients (carbohydrates, protein and fat) as indicated by the duration of the event and the lower intensity.

The successful execution of an ultra-endurance event is dependent on preparation, and attention is given to nutritional requirements, injury prevention, tissue regeneration, and avoidance of acute tissue trauma and overtraining. The training required for ultra-endurance events is no different from that required for other sports, in terms of the underlying principles. The holistic approach can be expanded into five areas that, when combined, culminate in an integrated view of performance—physiology, biomechanics, psychology, tactics and health/lifestyle.

The fundamental variables of physiologic stress are the intensity, duration and frequency of training. Within the training process, the correct balance of low-, medium-, and high-intensity movement is critical to the adaptation process. If too much moderate- or high-intensity training is undertaken, there is a significant risk of fatigue, leading to overreaching or overtraining. Training frequency refers to the number of training sessions within a given time frame, such as a day or a week. Training volume refers to the product of duration and frequency of training (usually in a week), and training load refers to the product of all three fundamental components—frequency, duration and intensity.

Carbohydrate diets range from 5 to 7g/kg/d (gram/body weight in kilogram/day) to 7 to 10g/kg/d three to four days before the competition. The higher the intensity, the more reliance there is on carbohydrates. During prolonged running events, 40 to 80 g/h usage has been reported, whereas usage of more than 90 g/h is not uncommon during cycling events. Most endurance athletes report better performances and minor gastrointestinal discomfort using liquid carbohydrates. Research has shown that fluid ingestion of 30 to 70g of carbohydrates per hour can maintain blood glucose oxidation and delay fatigue. A 7.5 to 12 per cent solution has been shown to minimise the chances of hypoglycaemia and maximise performance.

The modern ultra-endurance athlete requires sustenance to recover and prepare for upcoming training and racing. Rehydration and recovery of fluid balance after exercise, together with the timing and method of increased food intake to cope with heavy training, are essential for optimal performance.

The writer is consultant, orthopaedics, Fortis Hospitals, Bannerghatta Road, Bengaluru.