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Handgrip strength, dynapenia, and related factors in postmenopausal women

García-Alfaro, Pascual MD1; García, Sandra BSc1; Rodríguez, Ignacio MSc1; Pérez-López, Faustino R. MD, PhD2

Author Information
doi: 10.1097/GME.0000000000001872
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  • Editorial

Abstract

Muscle strength is an essential function of the human body, being a relevant component of health and physical fitness. It also refers to the ability of a muscle or muscle group to exert force against a resistance. Muscle strength is involved in many activities, daily tasks, maintenance of functional independence, and autonomy. Thus, regular physical activity adapted according to age is a preventive recommendation for healthy aging.1-3 Dynapenia defines the age-related loss of muscle strength, is the primary indicator of sarcopenia, and is a prognostic indicator of functional impairments in older adults.4 Thus, it is very important to maintain muscle strength to reduce functional limitations with age. The grip strength is considered a biomarker of frailty, in which there is an increase in an individual's vulnerability for developing dependency and/or mortality.5-7 In this context, it is convenient to dissociate the muscle mass reduction (sarcopenia) from the concept of muscle strength reduction (dynapenia).8

The pathophysiological mechanisms of muscle weakness can be compartmentalized into two factors. First the impairment of muscle system causes a deficit in the skeletal muscle force production and second the nervous system impairment that decreases the ability of voluntary muscle activation. Subsequently, it produces functional limitations and risk of physical disability.9 Muscle-skeletal changes are associated with aging, although other factors are involved in maintaining muscle strength and mass, such as hormonal profile, physical activity level, and nutritional status. So that old age, postmenopausal women, low body mass index (BMI), and low physical activity have been highly associated with dynapenia.8-10 Handgrip strength (HGS) measured with a hand dynamometer is a simple and accurate technique to assess muscle strength which is moderately related to muscular strength in other body sites. Therefore, it is considered a surrogate measure of more complicated approaches, such as arm and leg strength.11 The purpose of the current study was to investigate the prevalence of dynapenia and investigate factors associated with low HGS in postmenopausal women.

METHODS

Study design

This cross-sectional study was approved by the Center Institutional Review Board and performed from March 2019 to March 2020, in women who had their periodic gynecological check-up at the Department of Obstetrics and Gynecology of the Dexeus Women's University Hospital, Barcelona, Spain. Women were excluded if (1) they had early menopause (< 45 y) or surgical menopause; (2) were using menopausal hormonal treatment; or (3) had cardiovascular, liver, or renal diseases, a history of cancer, or physical disability. Finally, a group of 249 postmenopausal women aged 50 to 84 years, with at least 1 year of amenorrhea, participated in the study. We assessed their HGS, BMI, adiposity, bone mineral density (BMD), and physical activity. Smoking status and age at menopause were collected in the visit interview. The following blood biochemical laboratory parameters were also collected: calcium, phosphorus, vitamin D, and parathormone levels.

Muscle function assessment, body mass index, and adiposity

Physical activity was studied with the Spanish version of the short International Physical Activity Questionnaire. This tool includes seven-items that provide information about the number of days per week and the time spent in moderate and vigorous activities, walking and sitting. Physical activity categories were classified as low, moderate, and high levels.12 Muscle strength was assessed by HGS measured with a digital dynamometer Camry EH101 (Camry Industries Co. Ltd, Kowloon, Hong Kong) calibrated in kg. The measurement was carried out with the arm against the side and the elbow bent to a 90° angle. The dominant hand was assessed twice and the maximum value was recorded. For the current study, dynapenia was diagnosed when the dominant hand force was <20 kg, according to the cut-off recommended by the European Working Group on Sarcopenia in Older People Consensus.13

BMI was calculated as the weight in kilograms divided by the square of the height in meters after weighing and measuring participants without shoes and wearing a disposable gown. According to WHO criteria,14 BMI categories were established as low (<18.50 kg/m2), normal (18.50-24.99 kg/m2), and high that included both overweight (≥25.0-29.99 kg/m2) and obesity (≥30.0 kg/m2).

Adiposity was assessed by bioelectrical impedance analysis and expressed as a percentage of fat, using the Omron BF 306 monitor (Omrom healthcare Co Ltd, Kyoto, Japan) that measures arm-to-arm impedance along the shoulder girdle. The assessment was performed two times in the standing position, with the legs 35° to 45° apart and the arms extended forwards at a 90° angle with the trunk, using a disposable gown. Using the mean of the whole sample two categories were established: <40% fat and ≥40% fat.

Bone mineral density and biochemical parameters

BMD was measured by dual-energy x-ray absorptiometry (DXA) using the Lunar iDXA system (GE Healthcare, Chicago, IL). The measurements were carried out at the lumbar spine (L1-L4), femoral neck, and total hip, and the values were expressed as T-score. Following the WHO classification system,15 based on their lowest T-score the women were classified as normal BMD with a T-score > −1 standard deviation (SD), osteopenia with a T-score between −1 SD and −2.5 SD and osteoporosis with a T-score ≤−2.5 SD.

Blood samples were collected after an overnight fast. The plasma levels of calcium, phosphorus, vitamin D, and parathormone were measured by an automated COBAS 8000 modular analyzer System (Roche Diagnostics, Pleasanton, CA). The laboratory performs daily quality controls in accordance with the International Organization for Standardization, rule ISO 9001:2015 of each parameter. The results must be less than ±2 standard deviations with respect to the daily control value. Vitamin D levels were categorized in: ≥30 ng/mL (sufficient) and <30 ng/mL (hypovitaminosis D).16

Statistical analysis

Continuous outcomes were calculated as mean and standard deviation whereas percentages and numbers were used for categorical variables. Normal distribution was checked with the Shapiro-Wilks test. The Student t test or ANOVA test was used to compare average grip strength in categorical parameters. Pearson correlation was used to estimate the relation between numeric parameters with grip strength. Partial correlation adjusted by age was also calculated. A multivariable logistic regression model was constructed to analyze possible predictors of dynapenia. After testing several models, we chose the model that had a lower Akaike Information Criterion, taking into account associated factors: age, adiposity and T-score femoral neck. Results are reported as odds ratios (OR) and 95% confidence interval (95% CI). All analyses were performed using the R software (R Core Team, 2019). All the analyses were exploratory. No formal sample size calculation was performed.

RESULTS

The sample included 249 postmenopausal women, with a mean age of 62.7 ± 6.9 years and a mean age at menopause of 50.1 ± 2.7 years. The estimated average grip strength was 22.4 ± 4.0 kg, the whole BMI sample was 24.7 ± 3.8 kg/m2, and the total sample adiposity was 40.1 ± 5.3%. Mean of BMD measurements in the lumbar spine, femoral neck, and total hip were in the osteopenia ranges. The values of the biochemical parameters vitamin D, calcium, phosphorus, and parathormone were in the normal range (Table 1).

TABLE 1 - Biochemical parameters reported as mean ± standard deviation
Parameters Estimate (n = 249) 95% confidence Interval Reference ranges
Vitamin D 33.7 ± 11.8 32.2-35.2 30-100 ng/mL
Calcium 9.59 ± 0.35 9.5-9.6 8.7-10.4 mg/dL
Phosphorous 3.6 ± 0.4 3.6-3.7 2.5-4.5 mg/dL
Parathormone 44.0 ± 14.9 42.2-45.9 15-65 pg/mL

Table 2 displays the handgrip strength and related outcomes. Women aged ≥65 years had significantly lower HGS than those aged <65 years (P < 0.001), and there was a significant association between age at menopause and HGS (P = 0.005). Women with age at menopause ≥51 years had higher HGS values than those with age at menopause <50 years. There were no statistically significant differences between HGS and smoking status (P = 0.846) and BMI categories (P = 0.691). Regarding adiposity, women who had > 40% fat showed a significant association with low HSG (P < 0.001). There were no differences between HGS and vitamin D levels (P = 0.503). Women who performed low physical activity had lower HGS than those with moderate-high physical activity (P = 0.027). We also found that women with normal BMD had higher HGS than women with lumbar spine osteopenia-osteoporosis (P < 0.001), femoral neck (P < 0.001), and total hip (P < 0.001). There were no significant correlations between HGS with BMI and studied hormone and biochemical parameters.

TABLE 2 - Differences between handgrip strength (mean ± standard deviation) with regards to general characteristics of studied women, and vitamin D status
Parameters Categories n = 249 HGS P value 95% CI (mean differences)
Age (y) <65≥65 132117 23.7 ± 3.821.0 ± 3.8 <0.001 [1.7; 3.7]
Age at menopause (y) <51≥51 15693 21.9 ± 3.823.4 ± 4.3 0.005 [−2.6; −0.5]
Smoking NeverSmoker 20247 22.5 ± 4.122.3 ± 4.0 0.846 [−1.4; 1.2]
BMI (kg/m2) LowNormalHigh 4143102 22.1 ± 3.222.6 ± 4.022.2 ± 4.1 0.691 [−4.7; 3.5]Reference[−1.5; 0.6]
Adiposity (%) <40≥40 109140 23.7 ± 4.321.5 ± 3.5 <0.001 [1.1; 3.2]
Vitamin D (ng/mL) <30≥30 106143 22.2 ± 3.622.6 ± 4.4 0.503 [−1.3; 0.7]
Physical activity LowModerateHigh 1081329 21.8 ± 3.522.8 ± 4.324.9 ± 5.3 0.027 Reference[−0.01; 2.1][0.4; 5.9]
BMD Lumbar spine NormalOsteopeniaOsteoporosis 6811665 24.5 ± 3.721.6 ± 4.121.7 ± 3.6 <0.001 Reference[−4.1; −1.7][−4.2; −1.5]
BMD total hip NormalOsteopeniaOsteoporosis 10313412 23.6 ± 3.921.6 ± 4.121.2 ± 2.2 <0.001 Reference[−3.0; −0.9][−4.9; −0.1]
BMD Femoral Neck NormalOsteopeniaOsteoporosis 8315610 23.9 ± 3.621.7 ± 4.122.2 ± 3.1 <0.001 reference[−3.3; −1.1][−4.4; 0.9]
BMD, bone mineral density; BMI, body mass index; CI, confidence interval; HSG, handgrip strength.

Table 3 shows Pearson correlation coefficients (r) between HGS and covariates. HGS was correlated with age (r = −0.34, P < 0.001), age at menopause (r = 0.13, P = 0.035), adiposity (r = −0.27, P < 0.001), T-score lumbar spine (r = 0.26, P < 0.001), T-score femoral neck (r = 0.26, P < 0.001), and T-score total hip (r = 0.27, P < 0.001) (Fig. 1). Partial correlation adjusted by age has shown the same results.

TABLE 3 - Pearson correlation analyses between handgrip strength and age, age at menopause, adiposity, and bone mineral density (T-score)
Handgrip strength
Covariates r (Pearson correlation) P value Partial correlations P value
Age −0.340 <0.001 - -
Age at menopause 0.130 0.035 0.166 0.009
Body mass index 0.002 0.970 0.050 0.432
Adiposity −0.270 <0.001 −0.225 <0.001
Vitamin D 0.041 0.520 0.120 0.058
Calcium 0.110 0.075 0.124 0.051
Phosphorus 0.042 0.510 −0.005 0.941
Parathormone −0.010 0.870 0.025 0.699
T-score lumbar spine 0.260 <0.001 0.178 0.005
T-score femoral neck 0.260 <0.001 0.223 <0.001
T-score total hip 0.270 <0.001 0.205 0.001
Partial correlations with Pearson adjusted by age.

FIG. 1
FIG. 1:
Correlations between dominant handgrip muscle strength and age, age at menopause, adiposity, and bone mineral density (T-score).

Finally, a logistic regression analysis was fitted to estimate muscle strength <20 kg (dynapenia). Elderly women were more likely to have dynapenia. For every year in age, risk increased with OR of 1.09 (95% CI: 1.04-1.14). Likewise, women with higher adiposity had higher risk of dynapenia. For each 1% of adiposity, OR was 1.06 (95% CI: 1.00-1.13). On the contrary, women with higher femoral neck T-score were less likely to have dynapenia. OR of 0.53 (95% CI: 0.35-0.78) for each standard deviation. The prevalence of dynapenia in the study population was 31.3% (78/249).

DISCUSSION

We demonstrated in postmenopausal women aged 50 to 84 years that low HGS was correlated with age at menopause; adiposity (> 40% fat mass) and low BMD adjusted by age. Factors more likely associated with a higher risk of dynapenia were age and adiposity, whereas women with higher femoral neck T-score were less likely to have dynapenia.

Dynapenia and sarcopenia

Dynapenia is the age-associated loss of muscle strength not caused by muscular or neurologic diseases, whereas the term sarcopenia refers to the gradual reduction of muscle mass.4,8 Dynapenia might be considered an initial step of muscle dysfunction prior to sarcopenia.10 Barbat-Artigas et al17 reported that muscle strength is a better outcome of physical capacity than skeletal muscle mass, and dynapenic women have lower cardiorespiratory function than nondynapenic women even if they have the same muscle mass. Women begin the loss of muscle strength around the 5th and 6th decades of age.18,19 We previously reported in a group of young postmenopausal women (aged <65 y), a weak but significant inverse correlation between HGS and women's age.20 The present results showed that aging is related with the loss of muscle strength and this loss progressively decreases over the years. The aging process is associated with changes in qualitative and quantitative muscle mass.21,22 The loss of muscle quality occurs by a progressive decrease in muscle fiber type II, which plays an important role in anaerobic metabolism, likely represents the mechanism that initiates the declining muscle strength.23 However, age-related loss of muscle strength is only partially explained by the changes in muscle composition and reduction in muscle mass, therefore other physiologic factors would be involved in explaining muscle weakness in older adults,24 including gonadal ageing and reduction or lack of gonadal steroids25,26 and loss or dysfunction of motoneurons.27

The progressive decline in estrogen levels that occurs during the menopausal transition is also accompanied by significant changes in body composition, loss of muscle strength, and decreased BMD.10 Age at menopause has been related with HGS and an earlier age at menopause onset has been associated with an increased risk for presenting dynapenia.20 Thus, menopause could be considered as a factor directly related with muscle strength, regardless of age.25 The current study revealed that HGS had a weak decline correlated with age at menopause. Although it has been postulated that ovarian hormones protect against age-related loss of muscle strength in postmenopausal women, a meta-analysis suggests that hormone therapy did not protect against age-related lean body mass loss.28 In addition, the Canadian Longitudinal Study on Aging study reported that postmenopausal women who have never used hormone therapy have higher grip strength compared with those who ever used such treatment.29

Previous studies reported the prevalence of dynapenia is within a range of 7.7% to 52.4%. The variations in prevalence depend on the cut-off value, age, geographic location, and ethnicity of the population under study.30,31 The prevalence of dynapenia in our study population was observed to be 31.3%, so it is within the middle range. In the present study, age and adiposity were significantly associated with a higher risk of dynapenia and interestingly, we found that women with a higher femoral neck T-score were less likely to have dynapenia. There is likely a link between muscle strength and bone strength. In postmenopausal women, regular walking has no significant effect on spine BMD while it has a positive effect on the femoral neck BMD.32 Furthermore, a recent meta-analysis pointed out that low to moderate exercise is an osteogenic stimulus at the femoral neck.33 We can speculate that postmenopausal women with higher handgrip strength have, at the same time, some general benefit on femoral neck BMD characteristics due to better muscle function.

In recent years, there has been a growing effort to identifying risk factors contributing to female dynapenia, assessing BMD,34 vitamin D levels,35,36 cigarette smoking,37 bone mineral metabolism,38 comorbidities, socioeconomic status, and sociodemographic variables,39-41 with inconsistent results in many of these factors. Smoking which has been associated with increased protein catabolism, induces muscle wasting, reduces oxygen delivery, and impairs mitochondrial function. As a consequence, it increases muscle fatigue, since the ability of the muscular system to obtain energy is compromised.42 However, the relationship between smoking and muscle strength is unclear. Previous studies have observed the association between smoking and sarcopenia30 or dynapenia,43 while other studies found no association.44 In our study, smoking was not associated with HGS. However, in the Canadian Longitudinal Study on Aging cohort smoking was associated with a higher grip strength.29

Links between muscle mass and fat and bone mass

During the menopausal transition there are changes in body composition and in the distribution of fat. The changes in fat mass quantity were attributable predominantly to increasing age and menopause would not have a significant additional influence. After menopause, there is a decrease in the percentage of total fat in the legs and an increase in the measurements of central fat; therefore, it would be indicative of a change in the distribution of fat mass.45 To asses changes in body composition bioelectrical impedance analysis has been validated and it is considered as a good portable alternative to DXA. Also, it is widely available, rapid, inexpensive, easy to perform, readily reproducible and requires minimal operator training, being appropriate for epidemiological and clinical purposes.46,47

Controversies still exist when it comes to assessing the relationship between BMI and hand grip strength. Previous studies have found a weak correlation between BMI and grip strength48 contrasting with results of other studies which reported that HGS was not related with BMI.49

Although assessment of BMI in our study showed that the calculated mean BMI for all women was in the normal range, up to 40.9% of them were overweight-obese, and we did not find any correlation between BMI and handgrip strength. In our study, we observed that 56.2% of women had greater adiposity than the average and found a significant relationship between HGS and adiposity. A plausible reason might be the association between high fat mass content and poor muscle quality. Some previous studies revealed that excessive adipose tissue induces a proinflammatory state by the action of cytokines (e.g., tumor necrosis factor-alpha and interleukin-6) and higher plasma levels of cytokines are associated with lower muscle strength, muscle function, and muscle mass.50

Muscle strength and physical activity

Physical activity stimulates muscle protein synthesis and has beneficial effects on muscle mass, muscle strength and physical performance. Exercise has also shown beneficial effects on BMD and to delay the onset of osteoporosis.51 Exercise during middle age is associated with low prevalence of sarcopenia and is effective in maintaining muscle strength and physical performance in older age.52 The women in our study who performed moderate-high physical activity had greater HGS.

There are several studies with controversial results regarding the relationship between HGS and BMD. Some studies have reported a positive relationship between HGS and BMD,53,54 while others have not observed any relationship in postmenopausal women.55,56 The BMD analysis in our study revealed that mean T-scores were in the range of osteopenia and correlations were observed between HGS and the lumbar spine, femoral neck, and total hip BMD. These results are consistent with previous studies and reinforces the association between handgrip strength and BMD.34,53,54

Regarding bone mineral metabolism, some studies found associations between better muscle strength and higher levels of vitamin D, calcium, and phosphorous.38 In contrast, our study showed no relationship between HGS with bone mineral metabolism status, suggesting that the female phosphocalcic endocrine regulation is adjusted to the aging process. The presence of vitamin D receptors in skeletal muscle implies that vitamin D may directly target this tissue. Vitamin D can act on skeletal muscle through the proliferation and differentiation of muscle cells, and also affecting skeletal muscle contraction.57,58 Optimal serum 25(OH) vitamin D levels seem to be between 30 and 90 ng/mL (75-225 nmol/L), though there is no international consensus.16 The effect of vitamin D on muscle strength is not consistent. While some studies reported that vitamin D status has a significant positive correlation with HGS in postmenopausal women,35,59 other studies showed no significant differences.36,60 This may be related to vitamin D which affects muscle strength only when it is lower than a certain threshold. Muscle weakness or fatigue is a complaint linked to hypovitaminosis D, especially if serum levels are <15 ng/mL.61 In our cohort, there weren’t any women with extremely low levels of vitamin D.

Limitations and strengths

The present study has several strengths. First, it includes a relatively large sample size of postmenopausal women. Second, all BMD measurements were conducted with the same densitometer with daily quality control of the scanner performed by measurement of a phantom's density. Third, the biochemical determinations were measured in the same laboratory with quality controls in place. However, our study has also certain limitations, including its cross-sectional design and the use of one single technique to assess muscle function. Other measures to assess muscle strength would be necessary to fully assess muscle function, including gait speed and the study of diet protein content.62,63 Finally, we cannot omit that the studied population is a convenience sample of women with good general health.

CONCLUSIONS

The present study demonstrates that in postmenopausal women, low HGS is associated with age at menopause, low BMD (lumbar spine, femoral neck, and total hip), and adiposity adjusted by age. In the current sample, 31.3% of women had dynapenia. Both age and adiposity were significantly associated with a higher risk of dynapenia, whereas a higher femoral neck T-score was less likely to be associated with dynapenia. Handgrip strength is a standard test to evaluate muscle health status.64 Therefore, the routine implementation of grip strength measurement can be recommended for the study of changes in body composition and muscle strength under different treatments or physical activity programs in health care services.

Acknowledgments

This study has been done under the auspices of the Professorship in Obstetrics and Gynecological Research of the Hospital Universitario Dexeus, of the Universidad Autónoma de Barcelona.

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Keywords:

Adiposity; Age at menopause; Body mass index; Bone mineral density; Dynapenia; Handgrip strength; Physical activity; Vitamin D

© 2021 by The North American Menopause Society