Background
After reaching 30, aging leads to a progressive loss of muscular strength, muscular endurance, joint flexibility [
1], and balance [
2‐
4]. Age-induced musculoskeletal fitness (MSF; a comprehensive picture of upper- and lower body muscular strength and muscular endurance, and upper- and lower body joint flexibility) loss may inhibit older people from performing basic functional tasks such as lifting and moving objects, rising from a chair, and walking. MSF is therefore an important determinant of one’s capability to manage daily life activities and maintain functional independence [
5‐
7]. The incidence of falls increases with age; muscle weakness, impaired gait and diminished balance are the most significant risk factors for falling [
8,
9]. Fundamentally, fall avoidance challenges the ability to maintain the center of gravity over the base of support whether moving (dynamic balance) or stationary (static balance) [
8]. Static balance might therefore be an important component for predicting falls in older adults [
10]. Balance-and muscle strengthening activities seem to influence risk factors for falls by increasing muscle strength and balance ability [
11,
12]. In turn, such improvements increase one’s ability to remain independent with advancing age [
11].
Despite apparent connections between these variables, MSF and balance data collected on apparently healthy elderly, using standardized assessment methods, are scarce [
13,
14]. Current knowledge is primarily based on studies that have measured balance [
15], or handgrip strength [
16‐
20] separately. Few published studies have focused on an overall fitness evaluation (i.e. a more comprehensive picture of MSF and balance) among older adults [
21,
22]. These studies showed that all test scores declined with increasing age. Women scored better on the upper and lower body flexibility tests, whereas men performed better on upper and lower body strength- and balance tests [
21,
22]. The majority of the studies mentioned above have all been conducted outside the Nordic countries. In Norway, MSF- and balance data for normative values of individuals 65 years and older have not yet been published.
Physical activity (PA) levels decline significantly with age [
23‐
28]. In older individuals, loss of MSF and balance in combination with decreased PA levels is strongly predictive of falls [
29], disability [
30], hospitalization [
31], reduced quality of life [
32], and increased mortality [
1,
33]. There are a limited number of studies assessing the associations among MSF level, balance ability and objectively assessed PA levels in older adults. Also, some of the existing studies showed associations [
34‐
37], whereas others did not [
8,
38]. It is also somewhat difficult to distinguish which components of MSF (i.e. muscle strength and endurance, and joint flexibility) might be associated with PA level in the studies mentioned above. A study conducted by Aoyagi et al. [
38] showed that neither balance nor handgrip strength were related to daily step counts, whereas lower-extremity function (walking speeds and knee extension torque) was positively related to daily step counts in older adults. In contrast, de Melo et al. [
34] reported that balance and lower body flexibility were both associated with daily step counts in older adults (mean steps for 3 days: ≥ 6500).
Regular physical activity in older adults is associated with improved functional ability [
39], maintained mobility [
40], and reduced mortality [
41]. Therefore, more knowledge about musculoskeletal fitness- and balance ability in older men and women, and their association with physical activity level, may be of importance towards establishing future preventive health strategies in older adults.
Given these considerations, the aims of the present study were to; 1) describe musculoskeletal fitness and balance in a random national sample of Norwegian older individuals (65–85 years) focusing on age- and sex-related differences, and 2) investigate the associations among musculoskeletal fitness, balance, and objectively-assessed physical activity levels. Based on this the following hypotheses were provided: Among older Norwegian adults the younger individuals have better musculoskeletal fitness and balance ability compared with the older individuals. Older men have better muscle strength and balance compared with older women, whereas older women have better joint flexibility compared with older men. A higher physical activity level is associated with better musculoskeletal fitness and balance ability in older adults.
Discussion
The aims of the present study were to; 1) describe musculoskeletal fitness and balance in a random national sample of Norwegian older individuals (65–85 years); 2) examine age- and sex-related differences in musculoskeletal fitness and balance, and 3) to investigate the association among musculoskeletal fitness, balance, and objectively-assessed physical activity levels. The main findings were that the youngest participants (65–69 years) had significantly better static balance and muscular endurance in the trunk extensors compared with the older participants. Also, Norwegian older women (65–85 years) had significantly better upper and lower body flexibility, in addition to better muscular endurance in the trunk extensors compared with older men (65–85 years), whereas the Norwegian older men (65–85 years) had significantly better handgrip strength compared with older women (65–85 years). No sex differences were found in static balance. Further, a daily increment of 1000 steps was associated with significantly better static balance and muscular endurance in trunk extensors in older individuals (65–85 years).
We found significantly better static balance and muscular endurance in the trunk extensors among the youngest participants (65–69 years) compared with the older participants. Similar results have been found in one other study [
15]. This finding might be connected to differences in physical activity level across age groups. We have previously shown a 50 % higher physical activity level among the youngest participants (65–70 years) compared with the oldest participants (80–85 years) [
28]. Another possible explanation might be that increasing age leads to a progressive loss of balance [
2‐
4] and muscular strength and endurance [
1], mostly because of degenerative processes in the central and peripheral nervous system [
53] and qualitative and quantitative changes in the muscular system [
3]. For joint flexibility and handgrip strength we found no significant differences between the youngest and the older age groups, differences which have been observed in other studies [
16,
17,
21,
22]. This discrepancy might be a result of differences in socioeconomic status, cultural differences with respect to retirement age, infrastructure and degree of environmental security among the populations studied.
We found significantly better joint flexibility in older women (65–85 years) than in older men (65–85 years) which is in accordance with findings from previous studies [
21,
22,
37,
47,
54]. A possible explanation for these sex-related differences in joint flexibility might be related to differences in physical activity patterns among older men and women. We have previously shown that Norwegian older women spent more time (minutes) on low-intensity physical activity than did their male counterparts [
28]. This observation was confirmed in the present study because we found that women spent significantly more time each day performing low-intensity physical activity compared with the men (216 versus 190 min (
p = 0.001), respectively) (data not shown). We could therefore speculate whether daily low-intensity activities such as washing dishes, hanging washing, ironing and cooking might affect joint flexibility in older women by limiting the age- and activity-related deterioration. Other factors that might play a role regarding sex-related differences in joint flexibility are: anatomical and physiological differences, smaller muscle mass and different joint geometry and collagenous muscle structure [
55]. Older Norwegian men and women also seemed to have somewhat better mean flexibility in lower back and hamstring musculature than what has been reported among elderly in the USA [
47] and among elderly in Spain [
21]. This discrepancy might be explained by different test procedures as the two latter studies used chair sit and reach test, in addition to including a broader age range (60–85+). Shoulder joint- and arch flexibility also seemed to be somewhat better among older Norwegian men and women compared with older men and women in Spain [
21]. The exact same test procedure was used in the two studies. Therefore, the discrepancy might be related to differences in sample sizes and age ranges as Gusi et al. [
21] included 6.449 participants aged 60–94 years old.
Furthermore, we also found significantly better muscular endurance in the trunk extensors in women than in men. This sex-related difference might be related to biomechanical load differences during the static back extension testing, meaning that women’s shorter and lighter upper body compared with the longer and heavier upper body of men creates a shorter resistance arm resulting in relatively lower torque demands to maintain back extension in women than in men. This may make it easier for women to maintain the correct position for a longer period. In addition, women might be performing more domestic activities on a daily basis than men which require them to stand in an upright position (e.g. when washing dishes, hanging washing, ironing, and cooking) [
56]. This might affect the muscular endurance capacity in the trunk extensors by limiting age- and activity-related deterioration [
57].
Men had significantly better handgrip strength than women, which is in accordance with other cross-sectional studies where dynamometers were used [
16‐
19,
21]. Our population appeared to have somewhat better handgrip strength than what has been reported in studies from Brazil and Australia [
18,
19]. This discrepancy might be related to different selection of participants, cultural differences with respect to sex equality across countries (e.g. distribution of work regarding household and gardening), in addition to differences in test procedure, like measuring grip strength seated [
19] instead of standing in an up-right position which was done in the present study. It has to be mentioned though, that this comparison is based on a difference in age range (65–85 years versus ≥70 years), which also has to be taken into consideration when comparing our findings with the referred studies above.
We found no sex differences in static balance which is in contrast to one other study, showing significantly better static balance in older men than in older women [
54]. A possible explanation for not finding any sex-related difference in the static balance among older Norwegian adults might be related to their physical activity level. We have previously reported no sex-related differences in overall physical activity level within the different age groups among older Norwegian adults [
28]. This observation was confirmed in the present study, as we found no sex-related differences in the number of steps taken per day (7551 for women versus 7356 for men,
p = 0.7) (data not shown). Norwegian older men and women seemed to have better static balance compared with 60–80 year old Iranian men (
n = 36) and women (
n = 40) [
54]. Older Norwegian women appeared to have somewhat lower static balance results compared with what has been reported among 60–86 year old American women (
n = 71) [
15]. This variation in measured values for one leg standing time might be related to differences in the populations examined (e.g. sample size, high versus low functioning elderly) as well as procedural differences (e.g. shoes on, barefooted, dominant-, non-dominant leg, eyes open, eyes closed), which might affect the results [
58].
We found that a daily increment of 1000 steps was associated with significantly better static balance and muscular endurance in the trunk extensors in older Norwegian individuals. This knowledge may be of importance towards developing and initiating future preventive health strategies aiming at older adults. Attention should be given to balance and muscular endurance, as both components seem to have relevance to overcome activities of daily living [
8,
57]. A recently published study by de Melo et al. [
34] reported that agility/balance was significantly associated with pedometer-assessed steps taken per day when comparing older Canadian adults categorized as “high walkers” (mean steps for 3 days: ≥6500) with “low walkers” (mean steps for 3 days: <3000) (
n = 60, mean age 76.9 years). However, body sway/static balance was unrelated to accelerometer-defined measurement, expressed as daily step counts, in older Japanese men (
n = 94) and women (
n = 76), aged 65–84 years [
38]. In addition, hand grip strength was also unrelated to daily step counts in this elderly Japanese cohort, which is in line with our results. Furthermore, we found no association between a daily increase of 1000 steps and upper- and lower joint flexibility. In contrast, de Melo et al. [
34] reported significantly better lower body flexibility in “high walkers” than in “low walkers”. To our knowledge, no prior work has examined the associations between muscular endurance in the trunk extensors and physical activity among older adults, which makes our results rather novel. However, there are existing studies [
59‐
61] looking at the association between muscular endurance in the trunk extensors, physical activity and health related factors. These studies are all aiming at younger age groups, in addition to use of subjectively-assessed physical activity level through a questionnaire, which makes a comparison rather inappropriate.
One of the major strength of this study is the use of standardized musculoskeletal fitness and balance tests, with high validity, reliability, safety and feasibility. Furthermore, we used an objective assessment of physical activity, and the participants showed good compliance with the protocol and few data were lost because of insufficient wearing time or defect monitors. The participants achieved a mean of 6.6 days (SD 1.4) with valid activity recordings, and the mean wear time was 14.0 h per day (SD 1.2) [
28].
We acknowledge some limitations to our study. The relatively low participation rate might question the representativeness of the data. A drop-out analysis performed via registry linkage showed that the responses varied according to socio-demographic variables [
27]. Several test centers and test leaders were involved in the data collection and this might have influenced the reliability of the data. To minimize this limitation a test protocol together with illustrating test procedure posters were developed, followed by a pilot study where all the tests were accomplished prior to the main study. Also, the test leaders were trained in the test protocol and test procedures. Furthermore, there are limitations worth noting when interpreting accelerometry data [
62]. Walking technique must be taken into consideration because it can affect the validity of accelerometer step counts, especially in older individuals [
62]. It appears that some accelerometers can undercount activity in individuals with a nonstandard gait (e.g. upper body angled forward and knees bent during walking), thereby underestimating the activity level in these individuals [
63]. Another limitation is that only one test of static balance was included and that muscular strength was only examined via handgrip dynamometer. Also, as in any observational study, we have to be cautious in inferring causality based on our findings.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
SAA contributed to the conception and design of the study. BHH was responsible for the collection of the KAN data in corporations with colleagues at nine other test centers throughout Norway. HLS undertook the data analysis and drafted the manuscript. All authors provided critical insight, and revisions to the manuscript. All authors read and approved the final version of the manuscript submitted for publication.