To what extent does prolonged sitting time influence lower leg explosive power in older adults?
1. Introduction
1.1 Background
Insufficient amount of physical activity is one of the leading worldwide risk factors for increased global mortality. According to the World Health Organization (WHO), adults over the age of 65 years should be doing 150 minutes of moderate-intensity physical activity in a week. However, we still find that inactivity contributes to almost one in ten early deaths as it leads to heart disease (Physical Inactivity and Sedentary Behaviour Report, 2017). Recent studies have displayed the benefits of physical activity in older adults, such as improved quality of life, restored cardiac abilities, reduced function and cognitive decline (Katigbak et al, 2018). A meta-analysis found that in 2,932 older adults, those who took part in more exercise had a significantly lower arterial stiffness than their counterparts; who were more sedentary (Park et al, 2017). This meta-analysis provides a strong statistical power and summary of the picture being painted about the negative aspects of reduced physical activity, however we have to be cautious of the way the studies where chosen and identified as it was a meta-analysis, on top of, the heterogeneity of the results. In this case we may want to rely on more primary studies. Still, there is limited research on the impact that acute sedentariness may have on psychological and physiological (Lower Leg Explosive power (LLEP) factors within the older population. The aim of this research is to start to understand the affects it may have and how this can help inform current UK physical activity guidelines and health organisations in their understanding health needs for older adults.
Chronic Effects of Sedentary Behaviour
Sedentary behaviour is short periods of waking behaviour that uses a small amount of energy expenditure such as lying, sitting or reclining. Some of the most common examples of this type of behaviour come in the form of watching TV, reading and playing video games. However acute sedentary behaviour is not limited to home life but can be seen during travelling, talking, listening to music and at school/ work.
Sedentary behaviour is becoming more apparent, where older adults are found to be the most sedentary segment of the population, were household tasks and travelling are some of the main causes (Leask et al, 2015). TV viewing is also a popular form of pass time for increasing sedentary time. Figure 1 displays results from 275, 344 older adults across the UK, USA, Australia, Japan and Norway, showing that at least 56% of older adults watch over 2 hours of TV per day, as well as, 54.2% report 3 hours per day (Harvey et al, 2013). This is an alarming result taking into consideration that daily TV watching will be combined with many other sedentary activities in a day.
With sedentary behaviour patterns dramatically increasing, a growing amount of evidence are highlighting that as well as low physical activity being a major risk factor for chronic disease, increased sedentary time can also bring about similar consequences. Men who reported spending more than 10 hours a week in a car, had an 82% increased risk of CVD mortality, in comparison to those who spent less than 4 hours a week in a car (Warren et al, 2010). It has also been reported that an additional bout of sedentary activity can increase the risk of obesity by 13% and high abdominal fat by 26% (Byun et al, 2012). Figure 2 displays the results of a study expanding over 12 years, which found that in 17,000 Canadians adults, those who spent the most time sitting where 50% likely to die during follow-ups (Katzmarzyk et al, 2009). The advantageous use of a large sample pool can conclude that there is a strong causational pattern with increased sitting time and chronic effects. However, the lack of ethnic representation causes lack of generalizability, for older adult populations around the world. These findings cannot conclude that this pattern would be seen in African older adults, as they have many differences to Canadians such as genetics. (Will Add a study here to show one that can be more representative).
Ageing Effects on Muscle Power
Activities for older adults, such as walking up the stairs, is heavily reliant on the ability to produce quick and sufficient movement through muscle power output; in order to maintain living independently. However, muscle power is under threat, as sedentary behaviour continues to increase in older age. One of the most noticeable changes in older age, is the reduction in muscle size. When using an ultra-sound technique, there is found to be a 25-35% reduction in cross-sectional area of the quadriceps muscle in older men and women compared to younger populations (Young et al, 1984, 1985). This is further supported by Lexell et al (1995) study, discovering that the total number of fibers and muscle cross sectional areas (mm2) where almost half for a ninety-year old compared to a ten-year old. Ageing has also been liked to loss of muscle mass known as sarcopenia (Deschenes, 2012). 162 men and women, aged between 60 – 80 years old self-reported total sitting and TV viewing using a questionnaire and their maximal muscle strength of the lower limbs was assessed using three repletion maximum testing. They found a significant association in older age with poorer muscle function (30 s sit-to-stand, r=−0.18, P<0.05; FSST, r=0.38, P<0.001; TUG, r=0.17; P<0.05), reduced muscle strength (r=−0.30, P<0.001), functional muscle power (stair climb test r=−0.44, P<0.001) and lower total body lean mass (r=−0.20, P<0.05) (Gianoudis et al, 2015). Overall increased sitting time was associated with the increased risk of sarcopenia, yet the most stunning finding was that at every 1-hour increment of sitting, there was a 33% increase of sarcopenia. A big limitation of this study was the self-reported TV viewing time, which creates a chance for social desirability bias. Many of the participants could have given false viewing times to look more favourable to the researcher. Nevertheless, the consequences of reduced muscle size, power and sarcopenia has been well documented. It has been prevalent in causing functional deterioration, increased falls, decline in balance and loss of independence (Roubenoff et al, 0000). Sarcopenia impairs physical function and predisposes people to disability. With that being said, knowing that ageing naturally brings about muscle decline and the consequences of that, linking this with the consequences of sedentary behaviour, it highlights the likelihood that it will have a negative affect physiologically on older adults. The importance of exercising is similarly emphasised here, as muscle strength and mass can increase through the stimulation of protein synthesis during resistance training (Cauza et al, 2009).
Cooling of the Muscles
In addition to this concept, muscle power decline has also been linked with living in colder conditions. In healthy older women, it has been shown that there’s a decrease in physical performance due to cold indoor environments. When comparing the results (Figure), leg power in a 25-degree room temperature, compared to, a 15-degree room temperature, showed that leg power was lower in the colder room (Lindermann et al, 2014).
Similarly, the effects of seasonal temperatures and cooler indoor environments on 98 home bound people, saw that there was a significantly weaker physical performance for the residents in cooler houses compared to those in warmer environments (Hayashi et al, 2017). With that being said, AGE UK have reported that there is a large correlation between poor insulation and low indoor heating with winter deaths of older people and that almost 1 million people over the age of 65 have had to cut back on food shopping in order to cover utility bills (Later Life in the United Kingdom, January 2018). From this we can infer that there are many older adults who are living in colder conditions due to social factors, which in turn negatively impacts their muscle power. Merging this, with the knowledge that older adults are very sedentary, the importance of knowing how extreme the impact of this will have on their psychological and physiological bodily factors, will allow better informed physical activity interventions.
Not sure what to do with this paragraph? Maybe bring in bed rest research?
Through a cross-sectional design, using 30 healthy adult’s (n = 16 men, age = 79.0 ± 3.6 years and n = 14 women, age = 79.3 ± 3.4 years) we was able to look at the relationship between sedentary behaviour, physical activity and muscle quality. They found a distinctive positive correlation between sedentary time and lower limb adiposity in older men however they didn’t get the same finding for female participants. From their results, it can be suggested that those who have less sedentary time or breaking up sedentary behaviour are more like to have have enhanced leg extensor power.
Study Objectives
There is numerous evidence which supports the understanding that prolonged sedentary behaviour causes detrimental effects to health. However existing knowledge is very limited to understand the full extent to how psychological and physiological health in older adults is affected by acute bouts of sedentary behaviour; such as sitting. Therefore, in this study we aim to investigate these factors and how damaging the change is for older adults.
Research hypotheses:
Prolonged sitting will have a negative impact on Lower Leg Explosive Power (LLEP).