Longitudinal associations of objectively measured physical activity and sedentary time with leg muscle strength, balance and falls in middle-aged women

Figures & data

Table 1. Baseline characteristics of participants (N = 308).

Characteristics
Age (years)	50 (5)
Height (cm)	164.2 (6.1)
Weight (kg)	73 (15.3)
Body mass index (kg/m^2)	27.1 (5.5)
Education, n (%)
Primary/High school	90 (29)
High school/college	72 (23)
Tertiary institution	146 (48)
Employment status, n (%)
0 hr/week	33 (11)
≤ 0 h/week	55 (18)
> 0 h/week	220 (71)
Married/de facto, n (%)^a	237 (77)
Currently smoking, n (%)	22 (7)
Menopausal status, n (%)
Premenopausal	117 (38)
Perimenopausal	88 (29)
Postmenopausal	82 (26)
Not clear	21 (7)
Serum 25OHD level (nmol/L)	63.7 (23.2)
Lower limbs muscle strength (kg)	75.3 (29.2)
Timed up and go test (s)	5.3 (0.7)
Step test (steps)	18.6 (4.9)
Functional reach test (cm)	41.4 (6.2)
Lateral reach test (cm)	18.7 (3.9)
Valid accelerometer days (days)	7.34 (0.97)
Time (minutes/day), median (IQR)^b
Spent sedentary	535 (121)
Spent in light physical activity	267 (81)
Spent in MVPA	37 (33)

Notes: Values are presented as Mean (Standard deviation) unless otherwise stated. 25OHD = 25-hydroxyvitamin D; IQR = interquartile range; MVPA = moderate-to-vigorous physical activity; CPM = counts/min.

^a We combined married and living together and unmarried but living together as married/de facto, single, married but separated, unmarried, not living together, and divorced as not married/de facto.

^b Sedentary time was defined as those time less than 150 CPM, light physical activity as 150–1749 CPM, MVPA as more than or equal to 1749 CPM.

Figure 1. Multivariable mixed effects model for estimated leg muscle strength and balance measures with 95% CIs at baseline and five-year follow-up for pre-specified values of baseline MVPA. Baseline MVPA was standardised and pre-specified values were 0 and 1 standard deviation (SD). The coefficient for the interaction between baseline MVPA and follow-up time was demonstrated by the difference between the two slopes (black and gray solid lines), that is, the difference in the five-year change of the outcome for one-SD increase of baseline MVPA. The coefficient for baseline MVPA was demonstrated by the difference in estimated values at baseline (black and gray points at year 0). The models included baseline MVPA, follow-up time, and the interaction between baseline MVPA and follow-up time, adjusted for baseline age, weight (including its interaction with time), height, education, employment, marital status, smoking, menopausal status, serum 25-hydroxyvitamin D levels and baseline sedentary time.

Figure 2. Multivariable mixed effects model for estimated leg muscle strength and balance measures with 95% CIs at baseline and five-year follow-up for pre-specified values of 5-year change in MVPA. 5-year change in MVPA was standardised and pre-specified values were 0 and 1 standard deviation (SD). The coefficient for the interaction between 5-year change in MVPA and follow-up time was demonstrated by the difference between the two slopes (black and gray solid lines), that is, the difference in the five-year change of the outcome for one-SD increase of 5-year change in MVPA. The coefficient for 5-year change in MVPA was demonstrated by the difference in estimated values at baseline (black and gray points at year 0). The models included 5-year change in MVPA, follow-up time, and the interaction between 5-year change in MVPA and follow-up time, adjusted for baseline age, weight (including its interaction with time), height, education, employment, marital status, smoking, menopausal status, serum 25-hydroxyvitamin D levels and 5-year change in sedentary time.

Table 2. Associations between sedentary time and time spent in light physical activity and in MVPA with 1-year incident/injurious/multiple falls.

	Incident falls	Injurious falls	Multiple falls
	IRR (95% CI)	IRR (95% CI)	RR (95% CI)
Baseline
Sedentary time (per 83.22 min)	0.98 (0.78,1.25)	1.08 (0.80,1.47)	0.87 (0.60,1.26)
Light physical activity (per 63.35 min)	1.27 (1.02,1.57) *	1.10 (0.84,1.45)	1.33 (0.96,1.85)
MVPA (per 29.51 min)	1.02 (0.81,1.29)	1.04 (0.76,1.44)	1.01 (0.73,1.41)
5-year Change
Sedentary time (per 91.21 min)	0.8 (0.59,1.08)	0.87 (0.61,1.24)	0.84 (0.54,1.30)
Light physical activity (per 48.58 min)	1.25 (0.97,1.6)	1.23 (0.91,1.66)	1.21 (0.82,1.80)
MVPA (per 23.72 min)	1.18 (0.93,1.48)	0.86 (0.62,1.19)	1.08 (0.76,1.53)

Notes: MVPA = moderate-to-vigorous physical activity. IRR represent the average number of falls/injurious falls per person year in people with a standard deviation (SD)-unit increase in sedentary time and time spent in light physical activity and MVPA compared to the referent group. RR represent the risk of multiple falls in people with a standard deviation (SD)-unit increase in sedentary time and time spent in light physical activity and MVPA compared to the referent group. All models were adjusted for age, weight, height, education, employment, marital status, smoking, menopausal status, serum 25-hydroxyvitamin D levels at baseline; MVPA further adjusted when sedentary time or light physical activity was the exposure of interest; sedentary time further adjusted when MVPA was the exposure of interest. *P < 0.05, statistical significance.