Acute Effects of Sitting Time in Older Adults
Condition: Ageing
Study type: Observational

Summary: 
      United Kingdom (UK) physical activity guidelines for older people state that "All older
      adults should minimise the amount of time spent being sedentary (sitting) for extended
      periods" and "there is sufficient evidence to support a recommendation to reduce sedentary
      behaviour in older adults, but it is not currently possible to suggest a specific time
      limit." The aim of this study is to identify key physiological and psychological outcomes
      influenced by acute periods of inactivity and what older people feel after these acute
      periods of inactivity. The investigators' main objective is to determine, through direct
      measurement and self report, the acute functional and cognitive effects of differing periods
      of sitting time. A secondary objective is to inform older people, professionals and
      organisations working with older people and policy makers on what duration of sedentary
      behaviour will lead to adverse outcomes in older people. The investigators will recruit
      ambulatory men and women aged 70 y and over who will be studied on three separate occasions,
      approximately one week apart to complete sedentary bouts of 1 h, 2 h and 4 h in a randomised
      crossover design. The investigators will explore the relationship between sitting time and
      changes in lower limb explosive power(primary outcome) measured before and after each bout.
      Secondary outcomes will include timed chair rise; Timed Up and Go; blood pressure; perception
      of musculoskeletal comfort/pain, vitality; mood and cognitive function. The investigators
      will also measure the stress hormone cortisol in samples of saliva taken at the start of the
      sitting session, 1 h, 2h and 4 h later. Characterising the acute effects of sitting time in
      older adults will enable the design of interventions to reduce sedentary time as well as
      inform professionals and policy makers on what duration of sedentary behaviour will lead to
      adverse outcomes.
    

Detailed description: 
      Until relatively recently, sedentary behaviour was considered as the 'lower end' of the
      physical activity spectrum. However there is accumulating evidence from both epidemiological
      and observational studies which shows that sedentary behaviour per se rather than just low
      physical activity is also a major modifiable risk factor for chronic disease and predicts
      cardiovascular and all-cause mortality, independent of the amount of physical activity: A
      followup of the Australian Diabetic (AusDiab) cohort study showed a 46% increased risk of
      all-cause and an 80% increased risk of cardiovascular disease mortality in those watching
      four or more hours of television (TV) per day, compared with those watching TV for <2 h per
      day. In the Canadian Fitness Survey, a dose response relationship was shown between sitting
      time and cardiovascular disease and all-cause mortality. Significantly poorer long term
      mortality outcomes were found in those reporting spending most of the day sitting compared
      with those reporting less time sitting and this was consistent across all levels of self
      reported sitting time. Crucially, sitting time mortality relationships were apparent even
      among those who were physically active at other time points in their day. Although there is
      evidence supporting the longer term detrimental health effects of prolonged bouts of
      sedentary behaviour (sitting) across the age range, limited information exists with respect
      to the acute (or 'last bout') effects of sedentariness on the physiological and psychological
      health of older people.

      Interestingly the current UK physical activity guidelines state that "while there is
      sufficient evidence to support a recommendation to reduce sedentary behaviour in older
      adults, it is not currently possible to suggest a specific time limit". There is the need to
      be able to characterise sitting time in older adults in terms of acute functional and
      cognitive effects, as well as identify the main effects that older people perceive as being
      important after periods of sitting. Thus there is a possibility of generating specific advice
      to older people, but this requires the elucidation of dose response relationships between
      sitting and health outcomes to be defined during carefully controlled studies. Although these
      studies have yet to be conducted, it is possible to select 'key' outcome measures based upon
      established evidence derived from epidemiological and smaller scale observational studies
      (viz recent studies reporting a significant negative association between sedentariness and
      physical and psychological impairment in older adults) as well as from other 'models' of
      physical inactivity such as bed rest and limb unloading. One such outcome is skeletal muscle
      power output. The ability to quickly produce sufficient muscle power is of paramount
      importance for controlling body movements during mobility related activities in older people,
      such as standing up from a chair or stair climbing. Muscle power output is therefore a
      functionally relevant outcome of the utmost importance to the maintenance of physical
      independence. In addition, older people are less able to maintain core temperature, partly
      due to a reduced muscle mass yet it is known that reducing muscle temperature by only 1˚C can
      result in a decline of power output of up to 26%. Work by the current study group has
      recently shown a reduction in muscle power (45%), sit to stand performance velocity (9%),
      gait speed and maximum quadriceps strength after only 45 minutes sitting in a cool
      environment (15 degrees Celsius). It is not known if sitting (and consequent muscle
      inactivity) in normal temperature environments leads to reduced power in older people.
      However, older people talk of more difficulty getting out of a chair when they have been
      sitting for long periods, so muscle power may be implicated. In older people with joint pain,
      the benefits of keeping moving and not just sitting are clear.

      Although work on the effect of cold environments on cognition (dual task cost in walking
      speed and executive function using the trail making test) did not show any significant
      changes after 45 minutes exposure to 15 degrees Celsius in older people, little is known
      about effects on mood, well being or other cognitive and psychological outcomes of sitting.
      Associations between sitting and tiredness and depression have been shown in a longitudinal
      study of a middle aged Australian cohort in those who spent a total of >9 h/day sitting
      compared with those who spent <6 h/day sitting. However little is known about the effects of
      acute bouts of sitting. Although there is a body of evidence on the acute effects of physical
      activity, no published data reporting acute effects of sitting, or on dose response effects
      on psychological outcomes was found.

      Thus, the current understanding of the acute effects of sitting time is severely limited. The
      proposed study will inform the development, implementation and evaluation of future
      interventions to reduce sedentary behaviour in older people by identifying key elements of
      the immediate (acute) benefits of breaking up long periods of sitting, aiding engagement with
      older adults about immediate individual level benefits of reduced sitting and identifying
      outcome measures sensitive to changes in sitting time. Alongside views of older people, it
      will provide practical messages that can ensure more effective take up of an intervention
      among older people and effective advice for the professionals that work with older people.
      For example, for professionals working in residential home settings or on hospital wards/
      intermediate or transition care settings (post acute illness or surgery), the results of this
      research will give valuable information on desirable time periods for encouraging
      mobilisation.
    

Intervention name(s): Sedentary time
Intervention type(s): Behavioral
Observational model: Cohort
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Community-dwelling healthy older adults aged 70 years or over. Must be ambulatory with or
        without a walking aid.
      
Biospecimen description: 
      Saliva and serum from living donors