FISA have produced framework guidelines relating to the various exercise intensities that rowers might commonly train at. The table, Summary of FISA guidelines, summarises the defined exercise intensities. The table provides further information about the duration of the exercise, the percentage of maximum heart rate at which these are commonly found, descriptions of subjective feelings, and goes as far as suggesting lactate and heart rate ranges that are commonly observed.

The rationale for establishing exercise intensities stems from physiological research that found that training at different intensities produced a different response that, in turn, stimulated different changes within the body, across time. More importantly, such physiological adaptation will contribute toward endurance capacity and therefore to sports performance. This month's article summarises the physiological responses to training at UT2, and discusses its use in a training programme.

Oxygen utilisation level 2

This is low intensity UT2training and is also known as 'easy', 'recovery' or 'lower steady state.' The acute level of physiological stress is low and rowing at this intensity could be maintained for several hours. The muscles should not feel uncomfortable and breathing
rate should not be rapid or noticeable.
Nevertheless, heart rate may increase to approximately 60-70per cent of maximum heart rate (HRmax). This reflects the low but significant metabolic demand that must be met by the system of oxygen delivery and utilisation. Capillary networks open to flush the working muscle with blood from which oxygen is extracted fot use by the mitochondria (structures in the muscle cell that power energy release from energy rich foods).

Low intensity work prevents the early onset of exercise fatigue, therefore allowing sustained efforts to be performed. Capillaries and mitochondria increase in number following sessions of at least 20 minutes, but respond to a greater extent from sessions of 60-120 minutes.

There is no clear evidence to suggest that there is any difference in performing UT2 work in a continuous or interval manner in one training bout e.g. 90 mins versus 3x30 mins. Certainly the adaptation appears to be the same, but is is unusual for a trained athlete to need to stop exercising at this intensity (except perhaps to take fluids or to turn around the boat) and so most training is performed in a steady continuous manner. There may also be an element of psychological strengthening if an athlete `keeps going' for long periods.

Energy release comes mainly from fat during such outings and will develop further as biochemical adaptations improve oxygen and food use, allowing a conservation of the body's limited store of carbohydrate. Strong evidence is emerging that prolonged efforts will promote the selective use of slow twitch, type I (endurance type) muscle fibres above fast twitch type II (sprint type) muscle fibres. This altered muscle recruitment is accompanied by the development of fast fibres to possess more endurance qualities i.e. conversion of type IIb to type IIa fibres, and possible complete interconversions of fast to slow fibres. These conversions will only occur with several years of low intensity work.

Such changes make for a greater oxygen utilisation, and more efficient use of energy and the ability to endure. Other areas of the body, such as heart and lungs, are less affected, structurally and functionally by UT2 training, although improvements in efficiency may occur with time. Therefore, it is possible to conclude that UT2 work brings about changes at the periphery, in other words in the muscles.
UT2 forms the greatest percentage of training for many high performance programmes in rowing. Unquestionably this low intensity approach is effective in enhancing endurance but whether it is the most effective form of endurance training is still to be ascertained, and UT2 may well have drawbacks. There is a risk of immune suppression with prolonged and repeated low intensity. Therefore, a sudden introduction of large volumes of training or a lack of time to recover between training sessions may lead to a failure to adapt to training an/or an increased risk of infections or even fatigue syndromes. In contrast, short sessions of UT2 work are recommended to promote health and fitness for rehabilitation from injury and illness.

Some leading physiologists and coaches from other endurance sports, such as running, cycling and triathlon direct a greater proportion of training at the UTl/AT intensity than at UT2, for the improvements in endurance. These sports often use the equivalent UT2 exercise intensity as an `active recovery' session, exercising for no more than 40 minutes. This shift towards the UT1 exercise intensity is based upon research that indicates that you are able to reap at least the same physiological changes i.e. mitochondrial, capillary and enzymatic changes, from UTl as you can from UT2.

At the same time UT1 stimu~ lates the body with a higher training intensity, but within a shorter period of time. However, this research is based upon short term (i.e. weeks) of adaptation and may fail to account for the benefits of `mileage' that are probably related to improved recruitment and interconversions of muscle fibre types (and so are extremely difficult to quantify). In relation to UT2 work, the phrase of `putting miles in the bank' seems to encapsulate the idea of a down-payment or long term investment that is necessary to maximise the chronic adaptation.

Therefore, the evidence suggests that prolonged UT2 sessions of 60-120 mins are fundamental for long term development and early season preparation. However, there seems to be good reason for an increased emphasis upon higher intensity UTl work as the season progresses (January to March) and perhaps a phasing of some UT2 work to shorter `active recovery' sessions during the competitive season. Indeed, if training time is limited, long UT2 outings should be minimised in favour of the higher intensity UTl, which in terms of 'investment' may not mature with time but does take less time to earn!

Editorial by Steve Ingham