Association of Physical Activity and Gait Speed: Does Context Matter?

Abstract

Background: Physical activity (PA) is associated with gait speed, and both are recognized predictors of important health outcomes. The role of social context, such as PA of one’s spouse, in the association between PA and gait speed is largely unexplored. Methods: In our dyadic study of 69 couples, we objectively assessed each partner’s moderate to vigorous PA (MVPA) and gait speed. Associations of MVPA and gait speed were tested using actor-partner interdependence models in a structural equation modeling framework. Whether partners’ typically exercise together was examined as a moderator of these associations. Results: A nonlinear association was observed where higher MVPA was associated with faster gait speed, but only when MVPA was below average (husbands β = −.517; P = .002; wives β = −.483; P = .009). No moderating effects of exercising together were detected for husbands’ or wives’ MVPA on their own or their partners’ gait speed. Conclusions: In this investigation of couples, the association between MVPA and gait speed emerged only when nonlinear effects were considered. Findings suggest that the PA and gait speed association may be more nuanced than previously examined. Additional consideration of contextual factors that may alter the complex association between MVPA and gait speed is warranted.

“In this investigation of active couples, the association between MVPA and gait speed emerged only when nonlinear effects were considered.”

Introduction

Regular engagement in physical activity (PA) has many known health benefits, including preservation of gait speed throughout adulthood. ¹ Gait speed is of such health significance that it has been referred to as a “vital sign.” ² Specifically, gait speed provides significant information about current and prospective health status, and is strongly associated with fall-risk, hospitalizations, and mortality.^2,3 Associations between gait speed and function, including accelerated aging, are not limited to older adults, but also extend to generally healthy midlife adults.^4,5 In this study, we examined the association of PA and gait speed, and explored whether the context of PA (i.e., exercising together with a marital partner) moderates the PA—gait speed association.

Optimal gait speed relies on multiple physiological systems: cardiovascular, respiratory, musculoskeletal, nervous, and cognitive systems. ³ Given that PA is known to benefit the very systems that determine gait speed,^1,6 the positive association between PA and gait speed is well recognized in the literature.^4,5,7-9 Most studies explore the link between PA and gait speed in a dose-response manner, with an expectation that greater PA and faster gait speed are associated in a linear fashion.^7,9-11 Recent work, however, suggests this association may be more complex. ¹² In a large study of British adults, Keevil ¹² and colleagues examined participants’ gait speed across moderate-to-vigorous PA (MVPA) quartiles. A larger difference in gait speed was seen between participants achieving the two lowest levels of MVPA relative to the two higher MVPA groups. In light of these findings, we explore a non-linear association between MVPA and gait speed in married adults.

A second and novel aspect of this investigation is our examination of PA and gait speed in the context of close relationships. Marital partners often are similar in their health behavior choices, including their engagement in PA. ¹³ Partners also are similar in their readiness to adopt a more active lifestyle, ¹⁴ with one partner’s change in exercise associated with increased likelihood of a similar change in the exercise behavior of the other. ¹⁵ Notably, partners may elect to engage in PA together to show support for one another’s efforts to improve their health. In an investigation of shared exercise, partners who exercised together on a given day were more active on that same day than those who did not. ¹⁶ Drawing from this evidence, partners who exercise together may be more adherent to exercise routines, and incur more health benefits, than those who do not engage in exercise together.

In contrast to the literature on concordance in married partners’ PA, very few studies have explored gait speed in a relational context. One small study investigated walking speed among young adults with social partners (i.e., a friend or a romantic partner). ¹⁷ Findings showed that males significantly reduced their walking speed to match their romantic partner; however, their walking speed was not impacted when walking with friends. ¹⁷ No change was detected when females walked with their romantic partner or friend. ¹⁷ In a more recent study (using the same dataset as the current investigation), Cho ¹⁸ and colleagues examined changes in gait speed when married partners walked together and when they walked alone. Despite the potential for walking together to prompt a slower partner to speed up (potentially benefitting health) or a faster partner to slow down (potentially limiting health benefits of exercise), findings from this study revealed that both partners walked more slowly when walking together compared to walking alone. These findings suggest that the association between PA and gait speed may differ between couples who routinely exercise together and those who do not.

Current Study

Given the potential for shared exercise to promote PA of married partners, but also to reduce gait speed, we investigated PA and gait speed for both husbands and wives. Our dyadic study design also afforded the opportunity to examine cross-partner associations of one partner’s PA with the other’s gait speed, and to explore shared exercise behavior as a moderator of the association of PA and gait speed.

Methods

Participants

Couples were recruited to this study of physical activity in the context of committed relationships through flyers, newsletters, and social media. A sample of older couples (n = 39, age 50 years and over) was assessed in 2018. A second sample of younger couples (n = 35, age 25–49 years) was assessed in 2019 following similar study procedures. These samples were combined for this investigation. The following inclusion criteria were used: 1) both partners are able to walk in natural conditions, 2) partners are married or in a committed relationship, 3) partners live together in their home without assistance, and 4) both partners speak and understand English. Data analyses are based on 69 heterosexual couples with complete data.

Enrolled couples attended a one-hour session where signed informed consent was obtained, and study assessments were completed. During this session participants were also fitted with an accelerometer to wear for the next seven days. As an incentive for participation, each member of the couple received $25 USD. The University Institutional Review Board approved all study procedures and all participants signed an informed consent form before enrolling in the study.

Measures

Covariates

Self-administered questionnaires were used to assess age and self-rated health given recognized associations with both PA and gait speed. Self-rated health was assessed on a five point scale (1 = poor to 5 = excellent). ²

Exercise Together

A dichotomous variable indicating whether or not married partners exercise together was created from reports of each partner. Participants were asked whether or not they typically engage in exercise with their partner. If either or both partners indicated they exercise together, the couple was categorized as exercising together (n = 49, 71%).

Objective Physical Activity

Up to one week of PA was assessed with an Actigraph™ GT3X accelerometer. ¹⁹ Participants were instructed to wear the accelerometer on the right hip using a nylon belt during all waking hours except when bathing or swimming. Participants were also instructed to record wear time on a log sheet and to return the monitor in postage-paid envelopes.

Accelerometer data were screened for valid wear time using the Choi algorithm in ActiLife6^® software. ²⁰ Valid monitoring days were required to have ≥600 minutes of valid wear time (10 hours) per day, and participants were required to have at least four valid monitoring days to be included in the analysis. ²¹ A PA variable was created by summing the accumulated weekly minutes of MVPA using validated accelerometer cut points. ²¹ This variable was then divided by valid accelerometer wear time. Outliers were identified for the MVPA variable, and scores exceeding z = │3.29│SD above the mean were winsorized to the next highest score of the range of the distributions. ²²

Gait Speed

Following the protocol used by the Midlife in the United States Survey (MIDUS), ²³ participants were instructed to walk at their typical walking speed on a 25 ft (7.62 m) walkway, turn around, and walk back. Video analysis was used to determine the time taken to walk the 50 ft (15.24 m) distance. Gait speed was averaged across two trials, and it was calculated as (15.24/walk-time * 100), with units of cm/s.

Analysis

Actor-partner interdependence models (APIM) were used to estimate associations of each partner’s MVPA with their own gait speed (actor effect) and with their spouse’s gait speed (partner effect) in a structural equation modeling framework. ²⁴ First, linear and quadratic effects were tested to evaluate the form of the association between MVPA and gait speed. Next, exercise together was examined as a moderator of the associations between MVPA and gait speed.

Results

Participant Characteristics

Most couples were married (72.9%) with an average length of relationship of 20.0 ± 16.0 years (range = 1.5 to 54.0 years). Participants were middle-aged (husbands: 49.0 ± 7.3; wives: 47.4 ± 16.4), non-Hispanic white (husbands: 89.9%; wives: 88.4%) adults. Participants were well-educated with 88.6% of husbands and 94.1% of wives attending at least some college. On average, participants rated their health as “good” (husbands: 3.8 ± .8; wives: 4.0 ± .8) and were considered overweight based on their body mass index (BMI) (husbands: 28.0 ± 4.5; wives: 27.2 ± 7.1). Further, a majority of participants met or exceeded national PA guidelines (84% for both husbands and wives). ¹

Moderate-to-Vigorous PA and Gait Speed

In the initial linear model, neither actor nor partner effects of MVPA on gait speed were detected, contrary to our expectation (findings not shown). When quadratic effects of MVPA were added, however, both the linear and quadratic terms were statistically significant for each partner’s own MVPA on their own gait speed (i.e., actor effects; see Table 1; Figure 1 for husbands; Figure 2 for wives). Specifically, MVPA was positively associated with gait speed in the linear term for husbands (β = .434; P = .009) and for wives (β = .526; P = .005). MVPA was negatively associated with gait speed in the quadratic term for husbands (β = −.517; P = .002) and for wives (β = −.483; P = .009). No partner effects (i.e., association of one partner’s MVPA with the other’s gait speed) were detected.

Table 1.

APIM with Quadratic Estimates.

	Husband Gait Speed					Wife Gait Speed
	b	95% CI		P-value	β	b	95% CI		P-value	β
MVPA wife	.008	−.018	.033	.547	.117	.034	.010	.058	.005	.526
MVPA2 wife	.000	−.005	.006	.868	.032	−.006	−.011	−.002	.009	−.483
MVPA husband	.027	.007	.047	.009	.434	.014	−.005	.032	.156	.225
MVPA2 husband	−.007	−.012	−.003	.002	−.517	−.004	−.008	.000	.069	−.285
Self-rated health	.002	−.027	.031	.907	.011	.026	.000	.051	.049	.172
Exercise together	−.039	−.099	.022	.209	−.145	.031	−.024	.086	.272	.120
Age of husband	.000	−.002	.002	.976	−.003	.001	−.001	.002	.335	.109

Note. MVPA = Moderate to vigorous physical activity.

Figure 1.

Quadratic effects of husband and wife MVPA on husband gait speed (meters per second).

Figure 2.

Quadratic effects of wife and husband MVPA on wife gait speed (meters per second).

Exercising together also was examined as a moderator of the association between MVPA and gait speed. Contrary to our expectations, no moderating effects of exercising together were detected for husbands’ or wives’ MVPA on their own or their partners’ gait speed.

Discussion

In this investigation of active couples, the association between MVPA and gait speed emerged only when nonlinear effects were considered. For participants below mean levels of MVPA, engagement in higher levels of exercise was associated with faster gait speed. In contrast, at or above the mean MVPA there was no meaningful difference in gait speed related to levels of exercise. Associations of each partner’s MVPA with the other’s gait speed (i.e., partner effects) were not detected. Our findings of greater difference in gait speed at lower levels of MVPA are consistent with an earlier investigation. ¹² Together these findings suggest that the association between PA and gait speed is more nuanced than that reported in studies considering only linear effects.

We also explored the possibility that the social context in which exercise takes place would moderate the association between partners’ MVPA and gait speed. However, a moderating effect of exercising together was not detected. This finding differs from earlier work that demonstrated that walking with a romantic partner can alter gait speed.^17,18 It is important to note that our current study relied on partners’ self-reports of exercising together, whereas prior work investigated walking speed when partners’ were observed walking in various conditions (e.g., walking alone or with a partner).^17,18 Taken together, these studies highlight the importance of examining exercise and gait speed in the context of romantic (or close social) partners. Regardless of context, it merits mentioning that light intensity activity (such as slow walking) provides many health benefits compared to inactivity or sedentary behavior. ¹

Our study provides insight into couple’s PA behaviors; however, findings should be considered in light of study limitations. First, this sample was modest in terms of size and includes a convenience sample of participants who were specifically recruited together for a study of PA behaviors. As such, participating couples were highly active which could limit generalizability to less active couples. Additionally, our sample was comprised of heterosexual partners who were predominantly white and well-educated, limiting generalizability to more diverse samples. Lastly, our cross-sectional observational study design does not establish causality between MVPA and gait speed.

Our dyadic study adds to the growing literature examining the association of PA and gait speed in important ways. First, a more nuanced association between MVPA and gait speed is evidenced by our study, the work of Keevil and colleagues, ¹² and also by related work revealing a nonlinear association between leg strength and gait speed. ²⁵ Second, exploration of additional contextual factors that may alter the complex association between MVPA and gait speed is warranted.