Differences between achieving PA guidelines and QoL

One-way between groups ANOVAs were conducted to explore the relationship between different levels of activity and the normally distributed summary scores of MH and PH. A series of Kruskal-Wallis Tests were conducted on all of the 8 non-normally distributed subscales of QoL.

Participants were categorised into three PA groups (Low, Medium & High PA).

There was a statistically significant difference between the three levels of PA in PH [F(2, 76) = 4.37, p = 0.02, eta squared = 0.10] and physical functioning [² (2,76) = 7.18 p = 0.03].The effect size as outlined by eta squared between the groups for PH was medium. According to Cohen (1988), 0.01 is classified as a small effect, 0.06 is classified as medium and 0.14 is high. A planned comparison was carried out to investigate if those who met the guidelines (medium and high PA) differed significantly from those who did not achieve the guidelines on PH. This was found to be significant [F(1,76) = 8.55 p = 0.005], and indicates that achieving the guidelines is associated with higher PH.

Inspection of the means (see table 4.4.9) shows that the higher the category of PA the higher the PH. There were no other significant differences between any of the QoL subscales and PA levels.

134

Table 4.4.9a Descriptive statistics for PH for those achieving guidelines and not achieving guidelines

PH

Mean PH

SD N PH norm

of the UK population Mean (SD) Not achieving guidelines 40.74 10.57 28 50.9 (9.4) Achieving guidelines

(medium) 46.06 10.38 36 50.9 (9.4)

Achieving guidelines

(high) 49.67 7.70 15 50.9 (9.4)

As can be seen in table 4.4.9, the mean for PH in the high PA category reaches the mean norm for the UK general population.

A further one-way ANOVA was conducted to establish if there was a difference on PH for people in three conditions: those who achieved the guidelines through walking 150 minutes a week; those who achieved the guidelines through a combination of PA; and those not achieving the guidelines. There was a significant difference at the p<0.01 level in PH for the three different PA groups [F (2, 76)= 4.58, p = 0.01, eta squared = 0.11]. See table 4.4.9b for an overview of the means. A moderate effect size of 0.11 was calculated using eta squared. Post-hoc comparisons using the Tukey test indicated that the mean score for those meeting the guidelines through 150 minutes of walking (M = 44.50, SD = 10.91) was not significantly different from either those meeting the guidelines through a combination of PA (M = 48.43, SD = 8.97) or those not achieving the guidelines (M = 40.74, SD = 10.57). However, achieving the guidelines through a combination of PA was significantly different to not achieving the guidelines.

135

Table 4.4.9b Descriptive statistics for PH for PA groups of achieving the guidelines by walking 150 minutes, achieving guidelines by a combination of PA and not achieving guidelines

Guidelines PH

Mean PH

Standard Deviation

N

Not achieving

guidelines 40.74 10.57 28

Walking 150

minutes 44.50 10.91 17

Combination of PA 48.43 8.97 34

A one way ANCOVA was conducted to compare PH at the different categories of PA whilst controlling for age. After adjusting for age, there was no significant difference between the different categories of PA [F(2,71) = 2.69 p = 0.08 , partial eta squared = .07]. However, this was only just non-significant and maintained a medium effect size. The relationship between age and PH was moderate with a partial eta squared of 0.10. The mean ages for the different categories of PA in table 4.4.9c show that the mean age was lower in the high category of PA. Post-hoc comparisons using Tukey test indicated that mean age was significantly lower in the high PA group (M = 34.79 SD = 12.92) than in medium (M = 43.91, SD = 13.5) or low levels of PA (M = 46.23, SD = 12.87).

There was no significant difference in age between medium and low intensity groups.

Table 4.4.9c Age and category of PA

Guidelines Age

Mean Age

SD N

Not achieving guidelines

(low) 46.23 12.87 26

Achieving guidelines

(medium) 43.91 13.5 35

Achieving guidelines (high) 34.79 12.92 14

136 4.4.10 Correlations

The relationship between PA variables (total volume of PA, total amount of PA, volume, amount and frequency of walking, moderate intensity and vigorous intensity), QoL variables (PH, MH, general health, physical functioning, role physical, role emotional, bodily pain, vitality, mental health and social functioning), BPN variables (autonomy, competence and relatedness) and depression were investigated using Spearman’s rank order correlation.

Spearman’s rank was used because of the amount of non-normally distributed variables. For the purposes of these correlations the non-transformed total volume of PA and depression were used and included in the non-parametric correlations to keep it consistent with the other PA variables. See table 4.4.10 for an overview of the correlations.

As multiple correlations were undertaken, the use of a more stringent alpha level by Bonferroni’s adjustment was considered. Some statisticians argue that the more correlations or outcomes assessed, the greater chance of making a type 1 error (Bland & Altman. 1995). Implementing Bonferroni’s adjusted alpha makes it less likely that this will happen. However, it was decided not to use a Bonferroni adjustment as this assumes that all factors tested contribute to an overall null hypothesis (Perneger, 1998). This was not the aim of the current study which was to independently examine each theoretically-plausible factor in its own right (Cerin et al, 2009). In addition, decreasing the risk of type 1 errors increases the risk of type II errors (Perneger, 1998).

137

Table 4.4.10 Correlation table of PA, QoL, SDT and depression variables

Total

138

Table 4.4.10 shows that total volume of PA (energy expended METS) was significantly moderately and positively related to PH (r = 0.38, p = 0.001) and the SF-12 subscales of physical functioning (r = 0.42, p = <0.001), social functioning (r = 0.32, p = .005), and a significant, but small positive correlation for role physical (r = 0.27, p = 0.02). Total amount of PA was significantly moderately related to physical functioning (r = 0.37, p <0.01), social functioning (r = 0.36, p = 0.001), and role physical (r = 0.29, p = 0.01). However volume or amount of PA was not related to MH, other subscales of QoL, Depression, Autonomy, Competence and Relatedness.

Vigorous intensity PA was significantly moderately related to PH (r = 0.32, p = 0.004) and the SF-12 sub-scale of physical functioning (r = 0.37, p = 0.01).

Moderate intensity PA was found to be significantly associated with PH (r =0.24, p = 0.03) and the SF-12 subscale of physical functioning (r = 0.31, p = 0.005).

Walking was found to be moderately significantly related to the SF-12 subscale of Social Functioning (r = 0.37, p = 0.001) and a small but significant correlation was found for physical role (r = 0.27, p = 0.02). The frequency of walking was moderately positively associated with social functioning (r = 0.39, p <0.01).

The hypothesised mediating factors between PA and QoL - BDI depression scores and the Autonomy, Competence and Relatedness factors of the Basic Psychological Needs in General Scale – were not significantly related to PH.

The only significant correlation between any of the PA variables and any the BPNs was autonomy and the amount (r = .23, p = 0.045) and frequency (r = 0.25, p = 0.03) of moderate intensity PA. However, these relationships were weak.

The intention was to carry out multiple regressions to investigate the hypothesised mediating factors; however these were not calculated because there was not a strong significant relationship between PA and any of the BPNs or depression variables.

139

Demographic variables and relationship of PA and QoL variables.

To establish if any of the demographic variables acted as a confounder for any of the relationships between PA and QoL, partial correlations were undertaken. A Spearman’s rank partial correlation was used to calculate the correlations between the demographic variables and the PA and QoL variables which were found to be significantly correlated. Correlations were only conducted on variables in which there was a significant finding on both a QoL variable and a PA variable. This was only the case for status and age, see table 4.4.8.

A partial correlation was conducted to control for status in the relationship between physical functioning and total volume of PA. There was a moderate and significant correlation between physical functioning and total volume of PA after controlling for status (r = .37, p = .001). Upon inspection of the zero order correlation (r = 0.42) it can be stated that status had little effect on the strength of the correlation.

Age was controlled for in partial correlations between physical functioning, total volume of PA and vigorous PA. In addition the relationships between PH, total volume of PA and vigorous PA were also calculated whilst controlling for age.

There was a moderate significant partial correlation between total volume of PA and PH, whilst controlling for age (r = 0.31, p = 0.007). An inspection of the zero order correlation (r =0.33) suggested that controlling for age had very little effect on the strength of the relationship between these two variables.

There was a small non significant partial correlation between total volume of vigorous PA and PH whilst controlling for age (r = 0.16, p = 0.03). An inspection of the zero order correlation (r = 0.32) suggested that controlling for age had an effect on the strength of the relationship between these two variables.

Similar results were evident when controlling for age between physical functioning and total volume of PA and vigorous PA. A moderate significant partial correlation between total volume of PA and physical functioning (r = 0.38; p = 0.001) was found. The zero order correlation (r = 0.42) demonstrates

140

that controlling for age had very little effect on the strength of the relationship, between these variables.

Physical functioning and volume of vigorous PA whilst controlling for age found a small but significant positive correlation (r = 0.29, p = 0.01) with a zero order correlation r = 0.37. This demonstrates that age had very little effect on the strength of this association.

Although age appears to explain the relationship between vigorous PA and QoL, it did not explain the relationship between walking and any QoL variables, or moderate PA and any QoL variables. In addition, neither the volume nor amount of PA undertaken was related to age and therefore it was not perceived to affect the relationship between amount of PA and any QoL variables. The main finding was that age only has an impact on the amount of vigorous PA undertaken and older people have lower PH and physical functioning.