The amount of activity conducted is measured across three domains: frequency, duration and intensity. Research has tended to focus upon differing intensities, rather than the frequency or duration of exercise.
In terms of mortality rates, observational studies indicate there is an inverse linear dose-response relationship between the amount of physical activity and all-cause mortality (Lee and Skerrett 2001) and cardiovascular disease incidence and mortality, but no strong evidence for stroke incidence and mortality (Kohl 2001). A linear relationship between physical activity level and quality of life was reported by Kesaniemi et al. (2001). These systematic reviews included studies from Canada, Denmark, Finland, Germany, Israel, Italy, the Netherlands, Norway, Sweden, the United Kingdom and the United States. The reported relationship were seen across men and women and younger and older adults. In Lee and Skerrett’s analysis (2001), minimum adherence to the American College of Sports Medicine (ACSM) guidelines was associated with a 20-30% reduction in all-cause mortality. There was some support for reduced risk even below the guideline activity threshold.
There is level II evidence that a lower intensity home based program was as effective as a higher intensity program in improving functional capacity in middle aged adults (King, Haskell et al. 1991). Low intensity activity may produce some health benefits, but researchers recommend a progression to moderate intensity activity to optimise the health gains (Cress, Buchner et al. 2005). Generally speaking, the greater the usual energy expenditure, the lower the risk of all-cause mortality, after controlling for several confounding risk factors (Kesaniemi, Danforth Jr et al. 2001). The necessary intensity or ‘dose’ of physical activity to improve health or quality of life remains unclear (Spirduso and Cronin 2001). The physical activity threshold, in terms of intensity, duration and frequency, to reduce cardiovascular risk, is inconclusive (Kohl 2001). Several authors have reported a dose-response pattern (Morss, Jordan et al. 2004; Seynnes, Fiatrone Singh et al. 2004) for certain health outcomes (e.g. depressive status). A number of researchers have used low intensity activity, such as flexibility exercises as a control group (Binder, Schechtman et al. 2002). Fiatrone Singh (Fiatarone Singh 2002) comments:
‘The lack of appreciable objective benefits from low-intensity exercise (as commonly prescribed to older or frailer adults) should dissuade healthcare professionals from using doses and modalities of exercise that are below the threshold required fro physiological adaptation or therapeutic efficacy, even if they seem harmless. The lack of perceived efficacy from such low-intensity regimes can only serve to undermine the promotion of exercise as medicine and lead to dropout and discouragement on behalf of both patient and practitioner’ (pg 2089).
In terms of frequency, Perri and colleagues reported that more frequent exercise – 5-7 days vs. 3-4 days/week – resulted in greater total weekly physical activity without affecting attrition rates (Perri, Anton et al. 2002). For duration, there is emerging evidence concerning the protective capability of small bouts (less than 30 minutes) of physical activity. ‘Snackercise’, or accruing small snacks of activity, e.g. walking for as little as 10 minutes, may be as beneficial as longer duration activity (Murphy and Hardman 1998). Coleman and colleagues demonstrated that incremental activity, in blocks of as little as 5 minutes, can produce health benefits (Coleman, Raynor et al. 1999). This cumulative approach is likely to increase physical activity adherence (Dunn, Marcus et al. 1999). Others have reported that stair-climbing in up to six two minute episodes throughout the day can have similar health protective effects to one session of longer duration (Boreham, Wallace et al. 2000). An article from the Womens Health trial (Lee, Rexrode et al. 2001) revealed that time spent walking, rather than walking pace was predictive of reduced risk. At least one hour of walking per week was associated with lower CHD rates in these relatively sedentary women. The inverse association was even seen in those at high risk for CHD (e.g. with raised cholesterol levels, overweight and/or smokers). This evidence has guided the change in the message promoted by many physical activity guidelines, including the Australian National Physical Activity Guidelines (Department of Health and Aged Care 1999), that advocate individuals to accumulate at least 30 minutes of moderate-intensity physical activity throughout the day. This approach also reflects an attempt to make physical activity adoption more palatable in order to engage the most sedentary population groups, including older people, who have the most to gain from small changes to their lifestyle (Ekkekakis and Pettruzello 1999).
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The move to promote moderate intensity physical activity is supported by level III evidence from the American Women’s Health Initiative program (Manson, Greenland et al. 2002). Women who walked briskly or exercised vigorously at least 150 minutes per week had a risk reduction of about 30% for coronary disease. Compared to women who never or rarely walked, women who walked briskly had decreasing levels of risk (Table 8.1). Those who spent less time sedentary (categorised in hours spent sitting, lying down or sleeping) also tended to be at less risk. A large European case-control study confirmed the protective impact of physical activity for development of myocardial infarction (D’Avanzo, Santoro et al. 1993). The protection obtained from moderate intensity physical activity was similar to that from vigorous exercise. These findings are encouraging, given that moderate activity is likely to be more sustainable in older people.
Within a particular type and level of physical activity, the appropriate intensity for an individual will vary dependent upon a number of factors including health status and previous exposure to that activity. For example, a walking activity of moderate intensity might require walking briskly at 50 metres/minute for a well older person, whereas a frail older person with multiple health problems might find a walking activity at 10 metres/minute to be of similar self perceived (moderate) intensity. Therefore, intensity needs to be considered in the context of individual factors/ differences.
Table 8.1 Influence of walking pace on coronary disease risk.
|Relative risk *|
* compared to those who never or rarely walked, RR 1.0 Source: Manson 2002
Getting the physical activity message translated into action is clearly important. There is level II evidence, albeit in adult women, that the 10,000 steps message may be more productive than general advice to walk. Hultquist et al. (2005) conducted a trial where women were randomized to two message delivery modes: 10,000 steps per day or brisk walking for 30 minutes most days of the week. Participants were those walking 7000 steps or less in the run-in period. Both groups received closed pedometers to monitor actual steps taken. The steps group also wore a pedometer they could read. Both groups received weekly social support when they exchanged their pedometers. The steps group achieved the steps target and walked more on all days than the brisk walking group. Whilst the brisk walking group got close to this target on days they took exercise, this was not so on days they didn’t. The generalisability of the findings are limited by the participants’ homogeneity (they were largely overweight and Caucasian) and the short trial period (4 weeks). The authors point to several benefits of the step message: its specificity, and the motivating and adherence effects. The impact appeared to influence physical activity behaviour throughout the week, enabling greater integration of walking into daily life.
Table 8.2 summarises the current considerations regarding dosage of the different types of physical activity.
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