Age Moderates the Effect of Self-Paced Exercise on Exercise Adherence among Overweight Adults

Introduction

In the United States, approximately 70% of adults are overweight or obese (Hales, Carroll, Fryar, & Ogden, 2017). Regular physical activity (PA) plays an important role in preventing weight gain and in weight maintenance after weight loss (Donnelly et al., 2009; Donnelly et al., 2003; Donnelly, Jacobsen, Heelan, Seip, & Smith, 2000; Garber et al., 2011; Jakicic et al., 2001). Moreover, independent of any effects it may have on weight, regular PA has been shown to decrease risk of heart disease (Barry et al., 2014), type 2 diabetes (Ross, 2003), and cancers of the breast and colon (Boyle, Keegel, Bull, Heyworth, & Fritschi, 2012; Monninkhof et al., 2007), morbidities for which those who are overweight or obese are at increased risk. The benefits of regular PA may become more pertinent as people age, with mounting evidence demonstrating the protective effects of regular PA on age-related weight gain (Waller, Kaprio, & Kujala, 2008) as well as cardiovascular disease, certain cancers, dementia, sarcopenia, osteoporosis, and Alzheimer’s disease (Nelson et al., 2007; Warburton, Nicol, & Bredin, 2006).

The current U.S. Department of Health and Human Services guidelines recommend that adults expend at least 1,000 kcal per week in PA (Royall, Troiano, Johnson, Kohl, & Fulton, 2008), which can be obtained through 150 min per week of moderate-intensity PA, 75 min of vigorous-intensity PA, or some combination. However, current estimates suggest that only 3.5% to 43.5% of U.S. adults, and 28% of overweight or obese adults adhere to these recommendations, with estimates varying according to measurement methods (Adabonyan, Loustalot, Kruger, Carlson, & Fulton, 2010; Carlson, Fulton, Schoenborn, & Loustalot, 2010; Donnelly et al., 2009; Troiano et al., 2008; Young, Jerome, Chen, Laferriere, & Vollmer, 2009). Moreover, people across all World Health Organization regions become less active as they age (Hallal et al., 2012). Among U.S. adults, a more progressive decline in PA is seen after age 45 to 50 (Luke, Dugas, Durazo-Arvizu, Cao, & Cooper, 2011; Troiano et al., 2008). In essence, PA rates tend to decrease as people age and gain weight while the health benefits of PA become more pronounced.

Until recently, research on psychological contributors to PA adherence has been focused primarily on cognitive determinants, such as self-efficacy, outcome expectancies, attitudes, social support, social norms, and behavioral intentions (Marcus et al., 2006; Williams & Marcus, 2012). However, in the past two decades, there has been a gradual increase in attention to affective determinants of health behaviors in general (Williams, Rhodes, & Conner, 2018) and PA adherence in particular (Baldwin, Baldwin, Loehr, Kangas, & Frierson, 2013; Conner, Rhodes, Morris, McEachan, & Lawton, 2011; Ekkekakis, 2003; Ekkekakis, Hall, & Petruzzello, 2005b; Kiviniemi, Voss-Humke, & Seifert, 2007; Kwan & Bryan, 2010; Rhodes, Courneya, Blanchard, & Plotnikoff, 2007; Rhodes, Fiala, & Conner, 2009; Rose & Parfitt, 2012; Schneider, Dunn, & Cooper, 2009; Williams et al., 2008; Williams, Dunsiger, Jennings, & Marcus, 2012). One of the major challenges to increasing PA among unfit and/or sedentary populations is that many people within these populations experience a negative shift in affective valence (feeling good versus bad; Russell, 1980) from prior to PA to during PA (Ekkekakis, Parfitt, & Petruzzello, 2011). These findings appear to conflict with the popular notion that “exercise feels good”; however, positive shifts in affective valence tend to occur after PA rather than during PA (Ekkekakis et al., 2011). Thus, it is more accurate to say: Being done with exercise feels good, whereas exercise itself often feels bad.

Affective responses to PA may be important for understanding the low rates of PA. For example, previous theorists have posited that humans have a universal tendency to pursue behaviors that feel good and avoid behaviors that feel bad, a phenomenon known as the hedonic principle or psychological hedonism (Bentham, 1789/2007; Cabanac, 1971; Kahneman, Wakker, & Sarin, 1997; Williams, 2018). Indeed, a recent systematic review indicates that those who experience more negative (or less positive) affective responses to PA are less likely to repeat PA in the future, and thus more likely to drop out of PA promotion programs (Rhodes & Kates, 2015). Given that many people have an immediate negative affective response to PA, and a more negative response predicts lower PA behavior, it is unsurprising that there is a public health problem of physical inactivity (Lee, Emerson, & Williams, 2016).

One possible strategy to increase PA adherence is to circumvent the negative affective response to PA by recommending self-paced PA—that is, engaging in PA of a self-selected intensity (Williams, 2008). By self-selecting intensity rather than attempting to engage in PA of a prescribed intensity (e.g., moderate intensity), it is possible that one can optimize affective response to PA, thus making an aversive response less likely and, in turn, increasing the likelihood of continuing to engage in regular PA (Kwan & Bryan, 2010; Schneider et al., 2009; Williams et al., 2008; Williams et al., 2012).

Some recent evidence has accumulated to suggest that self-paced PA may lead to a more positive affective response and thus better adherence to PA programs. Several laboratory studies comparing the psychological response to self-paced versus prescribed intensity PA have shown that self-paced PA results in a more positive affective response (Ekkekakis & Lind, 2006; Parfitt, Rose, & Burgess, 2006; Rose & Parfitt, 2007). Moreover, in a recent randomized pilot study, adults assigned to a self-paced walking condition engaged in more minutes of PA than adults who were prescribed moderate-intensity walking, with a trend toward greater PA-based energy expenditure for the self-paced condition (Williams et al., 2015). In the latter study, better adherence to the self-paced condition was a function of a more positive affective response to self-paced versus prescribed moderate-intensity PA (Williams et al., 2016).

Few studies, however, have examined age differences in affective response to self-paced or prescribed intensity PA and the implications for PA adherence. In two laboratory studies, Barnett (2012) found that compared with younger adults, older adults showed higher positive engagement (e.g., enthusiastic, happy, upbeat) during 20 min of stationary cycling at 60% VO_2max, whereas Focht, Knapp, Gavin, Raedeke, and Hickner (2007) found no difference between age groups in affective response during 20 min of stationary cycling at 65% of VO_2peak. In a third study, DaSilva and colleagues (2010) found no age-related differences in affective responses to self-paced PA. However, to our knowledge, no study has examined age-related differences in affective response and adherence to self-paced versus moderate-intensity PA.

Thus, the goal of the present study was to test age as a moderator of the effects of self-selected versus prescribed moderate-intensity PA on PA adherence. We hypothesized (Hypothesis 1) that the recommendation for self-paced PA (as compared with prescribed moderate-intensity PA) would have a more positive effect on adherence to PA among older versus younger adults (Figure 1). We further hypothesized (Hypothesis 2) that any age-related differences seen in the positive effect of self-paced (compared with prescribed moderate intensity) PA on PA behavior would be explained by more positive affective responses to PA.

OPEN IN VIEWER

Figure 1.

Conceptual model.

Method

The present study was a secondary analysis of data from a previous randomized pilot study comparing self-selected with prescribed moderate-intensity PA among low-active overweight adults (Williams et al., 2015). Moderate intensity (64%-76% of age-adjusted maximal heart rate) was used as a comparison to self-paced intensity because it is recommended as an appropriate intensity for the general population by the American College of Sports Medicine (Thompson, Pescatello, & Gordon, 2010), the Center for Disease Control and Prevention (2008), and the World Health Organization (2010). The local institutional review board approved the study protocol.

Participants

Participants were community-dwelling adults (n = 59), ages 18 to 65, who were low-active (<60 min/week of structured exercise) and overweight or obese (body mass index [BMI] = 25.0-39.9 kg/m²), but otherwise healthy (i.e., no chronic disease) (Table 1). The participants had a mean age of 47.71 years (SD = 11.06), and a mean BMI of 31.93 kg/m² (SD = 3.99). Most participants were female (88%), employed (85%), reported household income ⩾ US$50,000/year (54%), and self-identified as non-Hispanic White (76%). There were no significant differences in baseline demographics between groups (p > .05).

OPEN IN VIEWER

Table 1.

Demographic Characteristics of Subjects by Total Sample and by Age 50.

	Total(n = 59)	Moderate intensity(n = 14)	Self-paced(n = 15)	Moderate intensity(n = 15)	Self-paced(n = 15)
Age (SD)	47.71 (11.06) years	Age < 50 years		Age ⩾ 50 years
Gender, % female	88%	92.9%	85.7%	80.0%	92.8%
BMI (SD)	31.93 (3.99)	31.83 (3.20)	32.52 (5.89)	31.36 (2.88)	32.04 (3.77)
Race/ethnicity, % non-Hispanic White	88%	85.7%	78.6%	93.3%	93.8%
Household income, % over 50,000	54%	64.3%	57.1%	46.7%	50.0%
Employment, % employed	85%	92.9%	71.4%	86.7%	87.5%

Note. BMI = body mass index.

Results

We tested for a moderation effect of age on the impact of self-paced versus prescribed moderate-intensity exercise on number of minutes of structured walking for exercise. We found significant moderating effects of age such that differences between self-paced and moderate-intensity conditions were more pronounced among older participants (main effect of condition: 6.14, SE = 2.54, p = .02; Condition × Age: −11.55, SE = 3.77, p < .01; Figure 2). As hypothesized, simple effects analysis showed that among participants ⩾50 years, those in the self-paced condition exercised 6 more min/day (p = .02) compared with those in the moderate-intensity condition. Alternatively, among participants <50 years, those in the moderate-intensity condition exercised 5.4 more min/day compared with those in the self-paced condition, with the latter difference of borderline significance (p = .05).

OPEN IN VIEWER

Figure 2.

Affective response to exercise, perceived exertion, and exercise minutes per day by age and intervention group.

We also examined affective response to exercise as a putative mediator of the moderating effects of age to determine whether effects of study condition on walking minutes by age were due to age-based differences in affective response to exercise. Contrary to our hypothesis, the effect of study condition on affective response to exercise was not moderated by age (p = .13) (Figure 2). The effect of study condition on perceived exertion also was not moderated by age (Figure 2).

Discussion

Empirical evidence regarding the benefits of self-paced walking for increasing PA is accumulating (Schneider et al., 2009; Williams et al., 2015; for review see Ekkekakis, 2009). Self-paced PA, in contrast to prescribed intensity PA, may influence affective response to PA, which may vary by age (Barnett, 2012; but see DaSilva et al., 2010; Focht et al., 2007). To our knowledge, the present study is the first to examine the moderating role of age on the effect of a self-selected versus prescribed moderate-intensity exercise on exercise adherence (Figure 1).

Consistent with our hypothesis, age moderated the effect of condition on minutes spent walking for exercise over a 6-month exercise promotion program. Participants who were older and told to self-select their exercise intensity exercised more minutes per week compared with older participants who were told to exercise at moderate intensity. In contrast, and unexpectedly, participants who were younger and told to exercise at a moderate intensity trended toward exercising more minutes per week compared with younger participants told to self-select their exercise intensity.

In an attempt to understand why the self-paced recommendation worked better among adults who were older, we investigated affective response to exercise as a putative mediator of the hypothesized moderating effect of age. A prior study using the present data showed that, among the full sample of participants, those in the self-paced condition has a more positive affective response to exercise than those in the prescribed moderate-intensity condition (Williams et al., 2016). However, the present analysis showed that the effect of condition on affective response to exercise was not moderated by age. That is, there was no differential effect of condition (self-paced vs. moderate intensity) on affective response to exercise as a function of age.

Taken together, the present findings show that adults who were older were more likely to exercise if they were given a recommendation to exercise at their own pace rather than specifically told to exercise at moderate intensity. The positive effect of self-paced exercise among older versus younger adults was not explained by affective response to exercise. Other possible reasons for this finding are that older adults, compared with younger adults, may have experienced more uncomfortable symptoms, such as shortness of breath, due to a longer span of de-conditioning, and therefore were more likely to exercise at a self-paced versus a moderate intensity. Although one might expect that such physical symptoms would impact affective response, it is possible that they instead had a direct effect on exercise behavior. In addition, there may have been other unmeasured variables that led to the differential effects of self-selected versus moderate intensity on exercise behavior among older versus younger adults, such as differences in expected benefits of exercising at a self-paced intensity, greater ability to engage in communal walking at a self-paced intensity, or the challenge of determining moderate-intensity levels. Additional research is needed to understand the role of these and other potential mediators of the differential effects of self-selected versus moderate intensities among older versus younger adults.

A strength of the present study is the use of EMA in a field-based experimental context, which, compared with the previous laboratory studies in this area, is likely to be more ecologically valid. The present sample also intentionally included only participants who were overweight and obese. This population was chosen because previous research shows that affective response to PA may be more negative among overweight and obese adults (Ekkekakis & Lind, 2006).

On the contrary, the relatively small sample size in the present study provided limited statistical power, particularly when testing effects of moderated mediation. Thus, the null findings for our second hypothesis could be the result of a type II error. In addition, the present study included a predominantly affluent female sample and thus the findings may not generalize to other populations.

Conclusion

While the health benefits of PA become more pronounced as people age and gain weight, PA rates tend to decrease. The present study provides preliminary evidence that recommending self-paced exercise may be a particularly effective strategy to promote exercise among overweight adults who are older (i.e., ⩾50), as compared with the prescription of moderate-intensity exercise as recommended in national guidelines. More research is needed to explore the potential mechanisms of this effect.