Study design and participants
This study is a part of the Estrogenic Regulation of Muscle Apoptosis (ERMA) study. The ERMA study is a population-based cohort study which consists of the data from women aged 47 to 55 years living in the city of Jyväskylä or neighbouring municipalities in Finland. A detailed description of participant recruitment has been reported earlier . Briefly, an invitation to participate in the study was sent to 6,878 potential participants randomly selected from the Finnish National Registry (Figure 1). Exclusion criteria were a self-reported body mass index (BMI) of >35 kg/m2, being currently pregnant or lactating, medical conditions affecting ovarian function (e.g., bilateral ovariectomy, estrogen-containing hormonal preparations), or chronic diseases or medications seriously affecting muscle function. Eligible participants (n=1,627) were invited to the laboratory and 1,393 women filled in the health screen questionnaire and gave fasting blood samples. Participants who had reported serious or unclear health conditions were examined by a physician to ensure safe participation in the physical performance measurements. The present analysis concerns women who performed at least one of the physical performance measurements acceptably and completed at least one mental well-being measurement (n=909).
All participants provided a written informed consent. The study protocol followed good clinical and scientific practice and the Declaration of Helsinki and was approved by the Ethics Committee of the Central Finland Health Care District (K-SSHP Dnro 8U/2014).
A detailed description of the measurement of physical performance – handgrip and knee extension force, low body muscle power, maximum walking speed and aerobic capacity – has been given earlier . Briefly, handgrip and maximal isometric knee extension forces were measured in Newtons. Handgrip force was measured on the side of the dominant hand with the participant seated in an adjustable dynamometer chair (Good Strength, Metitur, Palokka, Finland) with elbow flexed at 90º. The participants were instructed to squeeze the handle for 2-3 sec to produce maximum force. Knee extension force was measured with the same dynamometer chair with a knee angle set at 60° from full extension. Participants were encouraged to extend the knee to produce maximal force.
Lower body muscle power was assessed by a vertical jump on a contact mat. Vertical jumping height was calculated in cm from flight time (t): (g × t2) ÷ 8 × 100.
In all the above tests, three to five maximal attempts were performed and the best performance was taken as the result.
Maximum walking speed was measured over 10 m with the instruction to walk “as fast as possible” and timed with photocells. The fastest time of two trials, with self-selected rest of 30-60 seconds between trials, was taken as the result.
Aerobic capacity was assessed by the six-minute walking test. The test was conducted on a 20-m indoor track, and participants were instructed to complete as many laps as they could during 6 min. The distance covered in meters was used in the analysis.
Depressive symptoms were assessed with the 20-item Center for Epidemiological Studies Depression Scale (CES-D ). Participants were asked to rate the frequency of each symptom during the previous week. Each item was scored from 0 = seldom or never to 3 = almost all the time and a mean score for the 20 items was calculated. Higher scores reflect more depressive symptoms.
Positive and negative affectivity was assessed with the International Positive and Negative Affect Schedule Short Form (I-PANAS-SF ) comprising five positive affect adjectives and five negative affect adjectives. Participants rated each of these adjectives on a scale from 1 = does not describe me to 5 = describes me very well). Average scores ranging from 1 to 5 were calculated for each affect scale, with higher scores indicating a higher tendency to experience positive or negative affectivity.
Global cognitive judgments of one’s life satisfaction were measured using the 5-item Satisfaction with Life Scale . Participants indicate the extent to which they agree or disagree with each of the 5 items on a scale ranging from 1 = strongly disagree to 7 = strongly agree. The mean score for the five items was calculated, with higher scores indicating more satisfaction with life.
Current level of leisure physical activity was assessed on a seven-point scale ranging from household chores to competitive sports and with questions assessing leisure-time and physical activity patterns. The PA questionnaire has been described previously and has been validated in middle-aged women . Briefly, the response categories were: 1 = inactive, 2 = light activity 1 to 2 times per week, 3 = light activity several times per week, 4 = moderate activity 1 to 2 times per week, 5 = moderate activity several times per week, 6 = high activity several times per week, and 7 = competitive sports and related training several times per week. For the analysis, the seven response categories were recoded to form three levels of PA: low (categories 1 and 2), medium (3 and 4), and high (5 and 7).
Background and adjusted variables
Age was calculated from date of birth to the date of the first laboratory visit. Level of education was assessed by a single question and categorised as primary (primary school), secondary (secondary school) and tertiary (applied science degree, bachelor’s degree, nurse training, master’s degree and PhD).
Body height was measured in meters by a stadiometer with the participant wearing undergarments only.
Body fat was measured in percentage of body weight with a multifrequency bioelectrical impedance analyser (InBodyTM 720; Biospace, Seoul, Korea).
Menopausal status was determined based on monthly self-reported bleeding patterns and serum follicle stimulating hormone (FSH) concentrations following the Stages of Reproductive Aging Workshop (STRAW) recommendations . FSH assessments were performed from fasting serum samples which were collected between 8:00 and 10:00 AM. If the women had a menstrual cycle, then collection was performed during cycle days 1 to 5. Serum was separated by centrifugation for 10 minutes at 2.200x g. Systemic FSH was immunoassayed using IMMULITE 2000 XPi (Siemens Healthcare Diagnostics, UK).
A detailed description of the grouping by menopausal status has been reported earlier . Briefly, participants’ menopausal status was characterised as premenopausal if they reported a regular menstrual cycle and had FSH values <17 IU/L (M = 7.72, SD = 3.50); as early perimenopausal if they had FSH values from 17 to below 25 IU/L or if they reported an irregular menstrual cycle and had FSH values > 9.5 IU/L (M = 16.76, SD = 4.77); as late perimenopausal if they had FSH values in the range more or equal to 25 to 30 IU/L or if they reported occasional menstrual bleeding during the past 3 months and had FSH values >30 IU/L (M = 44.90, SD = 19.96); and as postmenopausal if they reported no menstrual bleeding during the past 6 months and had FSH values >30 IU/L or reported no menstrual bleeding during the past 3 months and had FSH values>39 IU/L (M = 82.48, SD = 28.82).
Menopausal symptoms were assessed with a structured questionnaire to determine whether participants had any of the following symptoms: sweating, hot flashes, sleeping problems, headache, joint pain, tiredness, mood swings, vaginal symptoms, urinary track problems, sexual problems, or any other symptoms. For the present analysis, responses were recoded into a dichotomous variable (menopausal symptoms/no menopausal symptoms).
Marital status was categorised as single, married or living with a partner, or divorced, separated or widowed. Parity was categorised as nulliparous, one or two children, and three or more children. Employment status was dichotomised as employed (paid or self-employed) or not regularly employed (studying, unemployed, working occasionally, retired, taking care of the home). A diagnosed mental disorder was self-reported as yes/no. Information on the use of medications that could influence mental well-being (N05, psycholeptics and N06, psychoanaleptics) was self-reported and coded according to the Anatomical Therapeutic Chemical Classification System . The codes represent respective dichotomous variables -users or non-users.
Participant characteristics are shown as means and standard deviations or as percentages. Multiple regression analyses were conducted to examine the association between the physical performance variables and dimensions of mental well-being. In model 1, regression models were adjusted for body height, fat mass percentage, menopausal status and symptoms, marital status, parity, employment status, self-reported mental disorders, use of psycholeptics and psychoanaleptics. In model 2, physical activity was added. These variables, deemed theoretically important, were justified based on our previous study with ERMA participants various associations between physical activity, physical performance measurements, and mental well-being [11, 12]. All analyses were performed with R, version 3.3.3 and the package sjmisc