Article by Dr Paul Batman P.hD
The new discipline of “sedentary physiology” or “inactivity physiology” is emerging as more information becomes available on the problems associated with sitting, inactivity and sedentary lifestyles.
Sedentary Behaviour is a Significant Health Hazard. Unique responses caused by prolonged sedentary behaviour that are the result of a lack of continual skeletal muscle contractile activity include:
With improved instrumentation it is now possible to measure what happens to the body during inactivity on a scale that was previously unavailable. For example, accelerometers/trackers can now be attached to joints to measure the entire range of movement including intensity, duration, frequency and movement patterns from sedentary to very vigorous activity.
Sedentary Physiology now occupies the lower end of the physical activity continuum focusing on the biological responses and processes that occur when stationary for prolonged periods and is now regarded as something entirely different, yet complimentary to Exercise Physiology that focuses on the responses of the body during movement.
Sedentary physiology has its own unique and specific effects on metabolism, bone mineral density and levels of cardiovascular and metabolic health.
Inactivity is distinct from moderate to vigorous physical activity (MVPA) (6-9 METs) and is characterised by a lack of low to moderate intensity movements (2-6 METs) throughout the day, while sedentary time is characterised by prolonged periods of sitting, stationary standing, reclining or lying at an intensity less than 1.5 METs.
To decrease sedentary behaviour prolonged inactivity must be substituted with increased movement opportunities of low to moderate intensity multiple times throughout the day.
Sedentary behaviour is classified by the following criteria:
<1.5 METs, <40% HR max, <20% HRR, <20% VO2max
RPE < 8 (6-20 Scale), RPE < 1 (0-10 scale)
Sedentary activities are those movements that usually involve sitting or lying/reclining and that have little additional movement and low energy expenditure. Most sedentary activities occur at home, travelling, at work and during leisure time.
Low intensity activity is classified by the following criteria:
- 6-3 METs, 40-55% HR max, 20-40% HRR, 20-40% VO2max
REP 8-10 (6-20 scale), RPE 1-2 (0-10 scale)
Low intensity activities do not cause any noticeable change in breathing rate and can be maintained throughout the day as they cause little fatigue. Low intensity activities provide limitless opportunities throughout the day to promote energy expenditure
Moderate intensity activity is classified by the following criteria:
3-6 METs, 55-70% HR max, 40-60% HRR, 40-60% VO2max
RPE 11-13 (6-20 scale), 3-4 (0-10 scale)
Moderate intensity activities are those that can be performed while maintaining a conversation uninterrupted. Moderate activities can be maintained for 30-60 minutes continuously or throughout the day if performed multiple times with rest periods.
Vigorous intensity activity is classified by the following criteria:
6-9 METs, 70-90% HR max, 60-85% HRR, 60-85% VO2 max
RPE 14-16 (6-20 scale), 5-6 (0-10 scale)
Vigorous activities are aerobic activities performed at an intensity where a conversation cannot be maintained or uninterrupted. Vigorous activities are generally performed for 30 minutes to 60 minutes.
High Intensity activity is classified by the following criteria:
>9 METs, > 90% HR max, > 85% HRR, > 85% VO2max
RPE > 17 (6-20 scale), > 7 (0-10 scale)
High intensity activities generally cannot be maintained for longer than 10 minutes at a time. High intensity activities are performed greater than ventilatory threshold (VT) or lactate threshold. Exercising at this intensity causes a significant contribution of anaerobic energy leading to increased levels of lactic acid.
Traditionally MVPA exercise has been the cornerstone for improvements in health and fitness. Over the past 15 years there has been an acute awareness of the increased time spent sitting in all aspects of life with over 200 studies examining its role in chronic diseases. One important observation has been the significant role that muscular activity plays in preventing and controlling disease. There is an increased awareness that the lack of skeletal contractile muscle activity is responsible for a growing list of chronic health concerns including obesity, Type 2 diabetes, cardiac health, inflammation and peripheral artery disease.
The overall consensus is that sedentary time should by replaced with low intensity multiple frequency intermittent muscle movements (2-6 METs) throughout the day even though the intensity is quite low. The signals that are causing the harm to the body from sedentary activities can be attenuated by extensive varied low intensity activities throughout the day by integrating movement back in to everyday lifestyles. This seems counterintuitive, as sitting and sedentary behaviour is a major part of our modern lifestyle with any side effects controlled by a formal traditional exercise program.
This approach has been suggested to improve the health outcomes of all people by increasing their activity levels even those who cannot engage in the traditional MVPA prescription. Many potent mechanisms for regulating disease are influenced by prolonged inactivity that is not corrected by traditional MVPA prescriptions (3-9 METs).
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