The relationship between health-related fitness and quality of life in postmenopausal women from Southern Taiwan.

BACKGROUND: Health-related fitness has been reported to be associated with improved quality of life (QoL) in the elderly. Health-related fitness is comprised of several dimensions that could be enhanced by specific training regimens. It has remained unclear how various dimensions of health-related fitness interact with QoL in postmenopausal women.
OBJECTIVE: The purpose of the current study was to investigate the relationship between the dimensions of health-related fitness and QoL in elderly women.
METHODS: A cohort of 408 postmenopausal women in a rural area of Taiwan was prospectively collected. Dimensions of health-related fitness, consisting of muscular strength, balance, cardiorespiratory endurance, flexibility, muscle endurance, and agility, were assessed. QoL was determined using the Short Form Health Survey (SF-36). Differences between age groups (stratified by decades) were calculated using a one-way analysis of variance (ANOVA) and multiple comparisons using a Scheffé test. A Spearman's correlation analysis was performed to examine differences between QoL and each dimension of fitness. Multiple linear regression with forced-entry procedure was performed to evaluate the effects of health-related fitness. A P-value of <0.05 was considered statistically significant.
RESULTS: Age-related decreases in health-related fitness were shown for sit-ups, back strength, grip strength, side steps, trunk extension, and agility (P<0.05). An age-related decrease in QoL, specifically in physical functioning, role limitation due to physical problems, and physical component score, was also demonstrated (P<0.05). Multiple linear regression analyses demonstrated that back strength significantly contributed to the physical component of QoL (adjusted beta of 0.268 [P<0.05]).
CONCLUSION: Back strength was positively correlated with the physical component of QoL among the examined dimensions of health-related fitness. Health-related fitness, as well as the physical component of QoL, declined with increasing age.

Introduction

Aging is often associated with functional limitations and disability. The aging process is typically characterized by a loss of muscular strength, reduction in joint mobility, reduction in cardiovascular capacity, and a decline in cognitive capacity.1 These physiological changes become more pronounced in postmenopausal women due to the development of osteoporosis and sarcopenia.2–4 These age-related declines can be assessed using health-related measures of fitness.5,6 Health-related fitness comprises several dimensions, including body composition, cardiorespiratory endurance, muscular strength, muscle endurance, agility, balance, and flexibility.5,7 Each dimension can be enhanced by using specific training regimens.8–13

Health-related quality of life (QoL) has been used to assess the overall status of patients; QoL has also been shown to be negatively correlated with age.14,15 Specifically, scores on physical functioning, physical role limitation, general health, and social functioning have been shown to decrease significantly with age in postmenopausal women.16 An inferior self-perceived QoL is associated with poor exercise adherence, which has been proposed to further jeopardize health-related fitness.17 Regular physical activity and/or exercise training programs are beneficial in minimizing the physiological alterations that occur with aging and contribute to improvements in overall health and well-being.18,19 It remains unclear how the various dimensions of health-related fitness are associated with QoL in postmenopausal women. Understanding which dimensions of health-related fitness impact QoL in the elderly could have significant implications in the prescription of exercise in this population, since different dimensions of health-related fitness can be enhanced using specific exercise training programs.8–13,19–23 The purpose of the current study was to investigate the relationship between different dimensions of health-related fitness and QoL in elderly postmenopausal women from Taiwan. We hypothesized an age-related decrease in health-related fitness and that reduced health-related fitness would be predictive of QoL in postmenopausal women.

Materials and methods

Participants

A total of 408 postmenopausal women from Chia Yi area and Yunlin County of Taiwan were enrolled in the current investigation between August 2010 and December 2012. Postmenopausal women were defined as having had no menstruation in the previous 12 months.24,25 The inclusion criteria of this study were: 1) postmenopausal women who were 2) healthy and 3) physically independent. The exclusion criteria were symptomatic cardiorespiratory disease, cognitive impairment or progressive and debilitating conditions, recent bone fractures, or any other medical contraindications to performing the fitness assessment.

Participants were divided into three groups stratified by age (group A: 50.0–59.9 years; group B: 60.0–69.9 years; group C: >70.0 years). The following anthropometric parameters were measured: height, body weight, health-related fitness, and QoL. All participants were Taiwanese from the Southern region of the country. This study was approved by the institutional review board of Chang Gung Foundation (IRB102-2419C), Tao Yuan, Taiwan.

Fitness assessment

Fitness of all subjects was evaluated using the HELMAS Physical Fitness Management System (O2RUN, CO., LTD., Seoul, Korea) at the Sports Medicine Center, Chang Gung Memorial Hospital at Chia Yi. Several dimensions of health-related fitness were evaluated, including muscular strength (grip strength and back strength); balance (closed-eye foot balance); cardiorespiratory endurance (step test); flexibility (sitting trunk flexion and trunk extension); muscle endurance (sit-ups); and agility (reaction time and side steps).26–29

Muscular strength

Grip strength and back strength were evaluated using a (dominant) hand and back dynamometer (HELMAS NH-3000D and NH-3000E). The better of two measurements was recorded.

Cardiorespiratory endurance

Subjects performed a 3-minute step test to evaluate cardiorespiratory endurance. Subjects were asked to step at a pace of 24 cycles per minute (metronome =96 beats per minute) using a 35 cm step box. After 3 minutes of stepping, subjects immediately sat down, and heart rate was recorded from 1 to 1.5 minutes posttest, 2 to 2.5 minutes posttest, and 3 to 3.5 minutes posttest (ACC-750B; Accuratus, New Taipei City, Taiwan). The results were recorded as time until exhaustion (seconds) and total heartbeats; these data were then plotted into a fitness index equation (FIE):

Balance

To assess balance, subjects closed their eyes and stood on their dominant leg on a balance-measuring instrument (HELMAS NH-3000H). The better time of two tests was recorded.

Flexibility

For sitting trunk flexion, subjects sat on a flexibility measuring instrument (HELMAS NH-3000G) with their heels positioned at the edge of the device. Patients then bent forward at the waist with their hands outstretched in front of them to push the measuring instrument as far as possible past their feet. The better of two tests was recorded (cm).

Trunk extension was evaluated with the patient in a prone position on a flexibility-measuring instrument (HELMAS NH-3000R). The better of two tests was recorded (cm).

Muscular endurance

The number of sit-ups performed in a 30-second period was recorded for subjects lying on a sit-up board with their knees bent at right angles and both hands positioned behind their necks (HELMAS NH-3000N). Subjects were encouraged to use only their upper body during each repetition.

Agility

A subject’s reaction time was measured with both their feet on a measuring instrument (HELMAS NH-3000I). Subjects were asked to jump vertically using both feet in response to a visual cue. The better of two tests was recorded (ms). The side step was measured using a labeled exercise board (HELMAS NH-3000J). The board was labeled at midline, with a parallel line 100 cm away (peripheral line) on either side of the midline. In alternating fashion, subjects were asked to perform lateral side steps to the left and right, touching the peripheral line with their feet. The total number of steps over the right or left peripheral line in 20 seconds was recorded.

QoL

QoL was assessed using the Short Form Health Survey (SF-36, Taiwan version).30 The SF-36 questionnaire is a multipurpose and short-form health survey, which is commonly used to evaluate patients’ QoL in clinical practice. A total of eight domains were evaluated in this questionnaire, including physical functioning, role limitation due to physical problems, bodily pain, general health, vitality, social functioning, role limitation due to emotional problem, and mental health. Additionally, the eight health domains can be used to provide a physical component summary and a mental component summary score.

Statistical analysis

All data analyses were performed using the Statistical Package for the Social Sciences for Windows (v 17.0; SPSS Inc., Chicago, IL, USA). All continuous data were presented as the mean ± standard deviation. Differences between groups based on age were calculated using a one-way analysis of variance (ANOVA) and multiple comparisons using a Scheffé test. A P-value of <0.05 was considered statistically significant. Trends and associations between variables were evaluated further using Spearman’s analysis of correlation. Multiple linear regressions with forced-entry procedure were performed to determine the predictors for QoL.

Results

A total of 408 subjects were enrolled in this study. The mean age of enrolled subjects was 64 years (range: 50–89 years). Mean subject body mass index was 25 kg/m2 (range: 16–38). An age-related decrease in body height (P<0.05) was observed (Table 1). With aging, dimensions of health-related fitness were reduced, including sit-ups, back and grip strength, side-step assessment, trunk extension, and agility (P<0.05) (Table 2). No differences were observed in the closed-eye balance test, sitting trunk flexion assessment, and step test between age-ranked groups. In QoL assessment, physical functioning, role limitation due to physical problems, and physical component score were also decreased in aged groups (P<0.05) (Table 3).

Table 1

Demographic data of participants

	All(N=408)	50–59 years(n=140)	60–69 years(n=162)	>70 years(n=106)	Scheffé
	Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD
Age (years)	64±9	55±3	65±3	75±4	A<B<C
Height (cm)	155±5	156±5	155±5	153±5	A>B>C
Weight (kg)	59±9	59±8	60±9	58±8
BMI (kg/m2)	25±3	24±3	25±4	25±3

Note: A: 50–59 years; B: 60–69 years; C: >70 years.

Abbreviations: BMI, body mass index; SD, standard deviation.

Table 2

Participant health-related fitness

Fitness test	All(n=408)	50–59 years(n=140)	60–69 years(n=162)	>70 years(n=106)	Scheffé
	Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD
Sit-ups (number performed)	2±4	3±4	2±4	1±2	A, B>C
Back strength (kg)	47±22	52±22	49±23	36±18	A, B>C
Grip strength (kg)	20±6	22±6	20±6	17±7	A, B>C
Side steps (number performed)	14±6	17±6	13±6	10±5	A>B>C
Reaction time (ms)	604±345	535±413	606±273	703±323	C>A
Closed-eye foot balance (s)	7±7	9±8	7±7	5±6	A>B, C
Sitting trunk flexion (cm)	6±11	6±11	7±10	4±12
Trunk extension (cm)	21±11	26±11	21±10	13±10	A>B>C
Step test (score)	64±11	63±10	65±12	62±11

Note: A: 50–59 years; B: 60–69 years; C: >70 years.

Abbreviation: SD, standard deviation.

Table 3

Participant quality of life (SF-36)

SF-36 (score)	All(n=408)	50–59 years(n=140)	60–69 years(n=162)	>70 years(n=106)	Scheffé
	Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD
PF	79±19	83±18	77±18	75±22	A>B, C
RP	58±44	63±41	62±43	45±46	A, B>C
BP	70±23	71±23	71±23	69±21
GH	56±20	57±20	55±20	58±19
VT	60±14	58±13	60±15	62±12
SF	87±17	85±16	87±19	88±16
RE	71±42	74±39	69±42	70±44
MH	69±17	68±18	69±18	73±16
PCS	47±9	49±9	47±9	45±9	A>C
MCS	49±10	48±9	48±10	51±10

Note: A: 50–59 years; B: 60–69 years; C: >70 years.

Abbreviations: BP, bodily pain; GH, general health; MCS, mental component summary; MH, mental health; PCS, physical component summary; PF, physical functioning; RE, role limitation due to emotional problem; RP, role limitation due to physical problems; SD, standard deviation; SF, social functioning; SF-36, Short Form Health Survey; VT, vitality.

In order to determine the relationship between each dimension of health-related fitness and QoL (physical and mental component scores), Pearson’s correlation analysis was performed (Table 4). A positive correlation between the physical component score of QoL and fitness was observed, specifically for sit-ups (correlation coefficient =0.177), back strength (0.334), grip strength (0.286), side steps (0.255), sitting trunk flexion (0.145), and trunk extension (0.297) (P<0.01 for all). A negative correlation between the mental component score of QoL and fitness was observed for closed-eye foot balance (r=−0.100, P<0.01). The different domains of fitness were also shown to be interrelated, specifically back strength correlated with grip strength, side steps, and trunk extension (r=0.603, 0.506, and 0.490, respectively, P<0.01).

Table 4

Correlation coefficients of fitness versus quality of life

	PCS	MCS	Sit-ups	Back strength	Grip strength	Side steps	Reaction time	Closed-eye foot balance	Sitting trunk flexion	Trunk extension	Step test
PCS	1
MCS	−0.150**	1
Sit-ups	0.177**	−0.038	1
Back strength	0.334**	−0.002	0.442**	1
Grip strength	0.286**	0.004	0.379**	0.603**	1
Side steps	0.255**	−0.042	0.444**	0.506**	0.401**	1
Reaction time	−0.177**	0.001	−0.266**	−0.315**	−0.247**	−0.329**	1
Closed-eye foot balance	0.096	−0.022	0.185**	0.289**	0.276**	0.348**	−0.166**	1
Sitting trunk flexion	0.145**	0.003	0.214**	0.192**	0.116*	0.236**	−0.168**	0.078	1
Trunk extension	0.297**	−0.040	0.357**	0.490**	0.340**	0.604**	−0.346**	0.256**	0.413**	1
Step test	−0.061	0.060	−0.025	0.099	0.001	0.040	0.010	0.092	0.000	0.032	1

Notes:

Statistically significant P<0.05;

statistically significant P<0.01.

Abbreviations: MCS, mental component summary; PCS, physical component summary.

To identify potential predictive factors for the physical and mental components of QoL, multiple linear regression analyses were performed using forced-entry procedure, adjusted for age. All dimensions of health-related fitness were selected and represented as independent factors in the multiple linear regression analysis. The regression model was checked for normality of residuals and displayed a normal distribution. Results demonstrated that back strength significantly contributed to the physical component of QoL with an adjusted beta of 0.268 (P<0.05) (Table 5).

Table 5

Multiple regression analysis of quality of life

Dependent variable		Unstandardized coefficients		Standardized coefficients	R2	ΔR2	95% CI
		B	Standard error	β			Lower	Upper
PCS	Intercept	42.155	3.428		0.103	0.103	35.411	48.899
	Sit-ups	−0.034	0.138	−0.016			−0.305	0.236
	Back strength	0.078	0.028	0.268*			0.023	0.134
	Grip strength	0.124	0.095	0.088			−0.063	0.310
	Side steps	0.082	0.095	0.061			−0.104	0.268
	Reaction time	0.002	0.002	0.056			−0.002	0.006
	Foot balance	−0.027	0.061	−0.025			−0.146	0.092
	Sitting trunk flexion	0.039	0.047	0.047			−0.054	0.131
	Trunk extension	0.060	0.055	0.075			−0.047	0.168
	Step test	−0.064	0.039	−0.087			−0.142	0.013
MCS	Intercept	40.458	4.170		0.015	0.015	32.254	48.663
	Sit-ups	−0.117	0.168	−0.047			−0.447	0.212
	Back strength	0.001	0.034	0.001			−0.067	0.068
	Grip strength	0.155	0.115	0.095			−0.072	0.382
	Side steps	0.006	0.115	0.004			−0.221	0.233
	Reaction time	0.002	0.002	0.045			−0.003	0.006
	Foot balance	−0.036	0.074	−0.029			−0.181	0.109
	Sitting trunk flexion	0.012	0.057	0.013			−0.100	0.125
	Trunk extension	0.032	0.066	0.034			−0.099	0.162
	Step test	0.054	0.048	0.063			−0.040	0.148

Note:

P<0.05.

Abbreviations: CI, confidence interval; MCS, mental component summary; PCS, physical component summary.

Discussion

The most important finding of the current study was that back strength was the best predictor of the physical component of QoL among the dimensions of health-related fitness in postmenopausal women (Figure 1). The current results are consistent with previous reports describing back strength as an important contributing factor for improved QoL in women with postmenopausal osteoporosis15 as well as the pivotal role of back strength in the improvement of QoL in the elderly.31–33 An increase in back strength resulting from exercise could improve QoL in postmenopausal women.31 Therefore, improved back strength is an important target for exercise training in an effort to enhance the physical components of QoL. Increased back strength, and any associated improvement in the physical component of QoL, may encourage adherence to prescribed exercise training regimens. The remaining dimensions of health-related fitness could be improved to achieve postural alignment, dynamic balance, functional mobility, and back extensor strength, which are associated with mobility limitations and an increased risk of falling in older adults.34–36 In the present study, we also demonstrated that back strength was positively correlated with grip strength, and that these domains probably share a common feature reflecting muscle strength. Trunk strength and endurance are important factors in the rehabilitation of ambulatory elderly patients.32 Recently, exercises specific for the abdominal core muscles have received attention for injury prevention, relief of lower back pain, and enhancing QoL.37,38 The current findings suggest that further strategies for improving muscle strength and endurance are needed.

Figure 1

Scatterplots showing the correlation between PCS of quality of life versus back strength.

Note: An increase in back strength significantly contributed to an increase in the PCS of quality of life.

Abbreviation: PCS, physical component summary.

In the current study, health-related fitness and the physical component of QoL declined with increasing age, while the mental component of QoL increased with aging. Furthermore, participants aged 50–59 years had greater fitness compared with their ≥60-year-old counterparts, consistent with previous reports wherein an age-related decline was observed in health-related fitness, including in muscular strength, flexibility, agility, and endurance.5,37 Age-related decreases in health-related fitness are important, since the resulting postural misalignment, balance deficits, and strength/power loss are associated with impaired functional mobility and an increased risk of falling.32,34,38 Therefore, muscle strengthening intervention may provide improved QoL and thus motivate the elderly to continue exercises that could minimize the age-related decline of fitness. Regarding the assessment of QoL, the current results are consistent with previous reports of the physical component of QoL being negatively correlated with age,16,33 whereas the association between the mental component of QoL and age remains controversial.16,33,39 Some studies have indicated that the mental component of QoL is not correlated with age;16,33 however, in subjects from rural Taiwan, we found an increase in the mental component of QoL with aging. These findings may be partially explained by reduced physical health and improved mental health among women living in rural areas compared with those women from an urban setting.39

Although an appropriate sample size and the homogeneity of subjects provided some strength in the present study, it was still limited by its cross-sectional design in terms of selection bias, ie, only associations were shown, not causality or temporal relationships. Further, this study was performed in a rural area in Southern Taiwan, where most participants performed agricultural work and had strong community support, factors that contribute to a lesser impact of hypokinetics and loneliness, which may result in a reduction in the mental component of QoL. Further studies should be performed to validate the current findings, with interventional studies performed to test the hypothesis put forward by the current study.

Conclusion

Back strength was an important contributor for the physical component of QoL among the dimensions of health-related fitness in postmenopausal women. Further investigation is warranted to delineate the effect of exercise intervention through targeted activities for back strength, such as Pilates, yoga, or core muscle strengthening exercises.