2.7 Evaluation of the Intensity and Duration of the Effort
Effort intensity is well correlated with heart rate (HR) in the absence of heart rhythm abnormalities or autonomic neuropathy. One way of defining the intensity of exercise is to state the actual HR as a percentage of the maximal HR. The maximal HR can be calculated or measured during a bicycle or treadmill stress test. Calculated (theoretical) maximal HR for all women or untrained men is 220 minus age. For trained men, it is 205 – 0.5 x age.38….
- Untrained 50-year-old man; maximal HR. 220 – 50 = 170 beats min-I.
- Trained 50-year-old man. Maximal HR. 205 – 20 = 185 beats min-I.
Table 2.1 Periods of ‘intense’ insulin activity of different insulin preparation and dosages. The
period of intense insulin activity is defined as the time between the moment when insulin:
activity reaches two thirds and the moment when it falls below two-thirds of the peak37 The
active period of the long-acting insulin analogues glargine (Lantus’) and detemir (Levernir)
is determined differently43 because they don’t have a real peak of action.
Exercise intensity is defined according to the following formula:
- low-intensity exercise, less than 60 per cent of maximal HR;
- moderate-intensity exercise, 60-75 percent of maximal HR;
- high-intensity exercise, more than 75 per cent of maximal HR.
Example 2: estimation of exercise intensity
- A 40-year-old woman, HR during exercise 80 beats min-I; maximal HR, 220 – 40 = 180 beats/min-I; HR/maximal HR = 80/180 = 45 per cent. This exercise is of low intensity.
Short – less than 20 min; medium 20-60 min; long – more than 60 min.
Characterization of the effort
Table 2.2 shows nine combinations of different durations and intensities of exercise. Every exercise session can be characterized with this chart.
2.8 Nutritional Treatment Adaptations
Without energy, there can be no exercise! The energy comes from stores located in the body or from ingested food or beverages. The diabetic person relies more than non-diabetic subjects on an adequate energy intake before, during and after exercise.
Although glucose represents only a part of the fuel metabolized during exercise, for simplification during patient education it is suggested that the energy expended must be replaced in the form of glucose, or carbohydrate equivalent, during and after exertion. People with diabetes whose insulin dosage has been adequately reduced need at least as much extra glucose during an effort as non-diabetics.39
Carbohydrate supplementation alone will prevent most hypoglycemic epsodes.14 Precise counseling in carbohydrate supplementation is extremely difficult, but Table 2.2 provides a guide for the approximate amounts of additional carbohydrate required for exercises of different duration and intensity. The amounts of carbohydrate have been validated in adults doing different activities [calisthenics, walking, mountain biking (personal data)].
The proposed extra carbohydrate intakes are rough estimates, with relative wide ranges. It is possible to increase the precision (make the range narrower) by comparing with the amounts listed in Table 2.3, which gives estimates of carbohydrate requirements for particular sports and activities and for three different body weights. 37
Although these tables give some indication of the energy expenditure associated with different activities and provide a starting point from which to make adjustments, at the end of the day there is no substitute for experience and for trial and (hopefully not too much) error. An important point is that the plasma insulin level at the start of exercise is never known. It can, however, be roughly estimated by observation of the slope between two blood glucose measurements at 15 and 30 min before exercise. A pronounced fall would indicate that additional carbohydrate is likely to be needed.
For endurance activities (several hours), the hourly need for extra carbohydrate will often reduce for two reasons:
1. A shift towards FFA consumption rather than glucose by the active muscle;
2. A drifting away from the period of maximal insulin action (in most cases) and decreased risk of insulin excess.
The relative amount of carbohydrate of FFA oxidized during an endurance effort will depend on the patient’s fitness level. Trained athletes oxidize FFA earlier and in greater amounts than untrained athletes and will spare carbohydrates in this way.
34.Grimm Jl. Ybarra J, Berne C, Muchnick S, Golay A. A new table for prevention of hypoglycemia during physical activity in type 1 diabetic patients. Diabet Metab. 2004; 30: 465-470.
36.Austernat E, Stahl T. Insulinpumppentherapie. Berlin: de Gruyter, 1989.
37.Berger W, Grimm n. Insulinotherapie. Comment gerer all quotidien les variations physiologiques des besoins en insuline. Paris: Masson, 1999.
38. Gordon dNF. Diabetes-your Complete Exercise Guide. Champain, IL., Human Kinetics, 1993, p. 39.
39. Sane T, Helve E, Pelkonen R, Koivisto VA. The adjustment of diet and insulin dose during long-term endurance exercise in type 1 (insulin-dependent) diabetic men. Diabetologia 1988; 31:35-40.
The new edition of this acclaimed title provides a practical guide to the risks and benefits of undertaking sport and general exercise for patients with diabetes.
Fully updated to reflect the progress and understanding in the field, the book features new chapters and material on insulin pump therapy and exercise, physical activity and prevention of type 2 diabetes, dietary advice for exercise and sport in type 1 diabetes, and fluid and electrolyte replacement.
For more information on this book and how to get a copy, just follow this link to Amazon.com, Exercise and Sport in Diabetes (Practical Diabetes), Dinesh Nagi 2nd Edition.
Copyright © 2010 by Blackwell Publishing Ltd, UK