3.1. Basic characteristics of the study population
The demographic and clinical characteristics of the study population, compared by sex, are listed in Table 2. The study included 623 males and 896 females. The average age of the study subjects was 57.9±13.3 years. The HGS was significantly higher in males than in females (40.2±8.2 kg vs 25.0±5.7 kg, p<0.01). Table 2 illustrates the consistently higher values in parameters of pulmonary function among males than among females.
Table 2. General characteristics of the study population
|
Males (n=623)
|
Females (n=896)
|
Total
|
Age, years
|
57.9±13.5
|
58.0±13.2
|
57.9±13.3
|
Handgrip strength, kg
|
40.2±8.2
|
25.0±5.7*
|
31.5±10.2
|
Height, cm
|
170.9±9.1
|
159.5±5.1
|
164.4±9.1
|
Weight, kg
|
73.0±12.6
|
61.4±10.4*
|
66.4±12.9
|
BMI, kg/m2
|
24.8±4.0
|
24.1±4.2
|
24.4±4.2
|
Waist circumference, cm
|
91.4±9.1
|
82.9±11.7
|
86.6±11.4
|
Hip circumference, cm
|
99.8±7.5
|
97.9±7.3
|
98.7±7.4
|
Pulse pressure, mmHg
|
50.9±10.1
|
53.0±11.2*
|
52.1±10.8
|
Hb, g/L
|
151.9±12.3
|
133.9±11.4
|
141.5±14.7
|
Plasma glucose, mg/dL
|
5.6±1.7
|
5.4±1.4
|
5.5±1.5
|
Albumin, g/L
|
45.9±5.0
|
45.8±4.5*
|
45.8±4.8
|
Alanine aminotransferase
|
24.4±17.6
|
19.0±15.9
|
21.3±16.8
|
Creatinine
|
83.2±15.0
|
65.5±11.5*
|
73.1±15.8
|
TC, mg/mL
|
4.6±0.9
|
4.8±1.0
|
4.7±1.0
|
HDL, mg/mL
|
1.3±0.3
|
1.5±0.4
|
1.4±0.4
|
Education, n (%)
|
|
|
|
≤High school
|
60.4
|
62.9
|
61.9
|
≥College
|
39.6
|
37.1
|
38.1
|
Regular exercise, n (%)
|
44.3
|
47.5
|
46.2
|
Drinking
|
51.2
|
25.7*
|
36.1
|
Cigarette smoking, n (%)
|
32.6
|
5.7*
|
16.7
|
Pulmonary function index
|
|
|
|
FEV 1 (L)
|
2.9±0.7
|
2.2±0.5*
|
2.5±0.7
|
FEV 2 (L)
|
3.3±0.7
|
2.4±0.5*
|
2.8±0.8
|
FVC (L)
|
3.3±0.7
|
2.5±0.5*
|
2.8±0.8
|
FEV 0.5 (L)
|
2.3±0.6
|
1.7±0.4*
|
2.0±0.5
|
MEF 25 (L/s)
|
1.3±0.6
|
1.1±0.5*
|
1.2±0.6
|
FEV 3 (L)
|
3.4±0.8
|
2.5±0.5*
|
2.8±0.8
|
VC max (L)
|
3.6±0.7
|
2.6±0.5*
|
3.1±0.8
|
VC IN (L)
|
3.5±0.8
|
2.6±0.6*
|
3.0±0.8
|
MEF 50 (L/s)
|
3.7±1.4
|
3.0±1.0*
|
3.3±1.2
|
VC EX (L)
|
3.4±0.8
|
2.5±0.6*
|
2.9±0.8
|
MEF 75 (L/s)
|
6.0±1.8
|
4.7±1.2*
|
5.2±1.6
|
MVV (L/min)
|
80.3±27.8
|
65.7±20.3*
|
71.89±24.9
|
*p<0.01 for comparison with males. BMI: body mass index, Hb: heamoglobin, TC: total cholesterol, HDL: high-density lipoprotein, FEV 0.5/1/2/3: forced expiratory volume in 0.5/1/2/3 second, FVC: forced vital capacity, VC IN: inspiratory vital capacity, VC EX: expiratory vital capacity, VC max: maximum value of vital capacity, MEF 25/50/75: maximum expiratory flow rate at 25 %/50%/75% vital capacity, MVV: maximum ventilation volume
3.2. Handgrip strength and pulmonary function both decline with age
We divided the subjects into two groups based on age: the younger group (<60 years) and the elderly group (≥60 years). A comparison between the two groups regarding HGS and pulmonary function is shown in Table 3, and the correlation coefficients between age and parameters are also listed. The average HGS differed significantly between the younger group and the elderly group (33.3 kg vs 27.6 kg, p<0.01). The pulmonary function of the younger group was also better than that of the elderly group as well.
In the linear correlation analysis, we found that HGS was significantly correlated with age (r=-0.30, p<0.01), and parameters of pulmonary function were strongly negatively correlated with age, especially FEV 1 (r=-0.55, p<0.01), FEV 2 (r=-0.53, p<0.01), FVC (r=-0.50, p<0.01), FEV 0.5 (r=-0.53, p<0.01), and MEF 25 (r=-0.60, p<0.01).
Table 3. Comparison of handgrip strength and pulmonary function between different age groups
|
Younger group
(<60 years)
|
Elderly group
(≥60 years)
|
r
|
Handgrip strength
|
33.3±16.4
|
27.6±9.4*
|
-0.30
|
FEV 1 (L)
|
2.8±0.6
|
2.2±0.6*
|
-0.55
|
FEV 2 (L)
|
3.1±0.8
|
2.5±0.7*
|
-0.53
|
FVC (L)
|
3.1±0.8
|
2.6±0.7*
|
-0.50
|
FEV 0.5 (L)
|
2.2±0.5
|
1.7±0.4*
|
-0.53
|
MEF 25 (L/s)
|
1.3±0.6
|
1.1±0.5*
|
-0.60
|
FEV 3 (L)
|
3.2±0.8
|
2.6±0.7*
|
-0.47
|
VC max (L)
|
3.4±0.8
|
2.7±0.7*
|
-0.46
|
VC IN (L)
|
3.2±0.8
|
2.7±0.8*
|
-0.44
|
MEF 50 (L/s)
|
3.8±1.1
|
2.8±1.1*
|
-0.50
|
VC EX (L)
|
3.1±0.8
|
2.6±0.7*
|
-0.41
|
MEF 75 (L/s)
|
5.7±1.5
|
4.8±1.5*
|
-0.39
|
MVV (L/min)
|
79.6±24.1
|
64.6±23.4*
|
-0.37
|
*p<0.01 for comparison with males;
r is the correlation coefficient between parameters and age.
3.3. Relationship between pulmonary function and handgrip strength
We analysed the correlation coefficients between parameters of pulmonary function and HGS in Table 4. As shown, HGS was positively related to almost every parameter of pulmonary function. VC (including VC max, VC IN and VC EX), FEV (including FEV 3, FEV 2, and FEV 1) and FVC showed large correlation coefficients with HGS, and the order of the correlation coefficients was as follows: VC max (r=0.72) > VC IN (r=0.71) > FEV 3 (r=0.70) > FVC (r=0.69) = FEV 2 (r=0.69) > FEV 1 (r=0.65) = VC EX (r=0.65). Therefore, we selected VC max, FEV 3 and FVC as three representative parameters to analyse the relationship between HGS and pulmonary function.
Table 4. Correlation between parameters of pulmonary function and handgrip strength by sex
Parameters of Pulmonary Function
|
Males
|
Females
|
Total
|
VC max
|
0.48
|
0.51
|
0.72
|
VC IN
|
0.47
|
0.50
|
0.71
|
FEV 3
|
0.48
|
0.50
|
0.70
|
FVC
|
0.49
|
0.50
|
0.69
|
FEV 2
|
0.48
|
0.52
|
0.69
|
FEV 1
|
0.48
|
0.46
|
0.65
|
VC EX
|
0.42
|
0.43
|
0.65
|
FEV 0.5
|
0.45
|
0.43
|
0.62
|
MEF 75
|
0.34
|
0.35
|
0.52
|
MVV
|
0.37
|
0.34
|
0.44
|
MEF 50
|
0.34
|
0.30
|
0.40
|
MEF 25
|
0.31
|
0.29
|
0.30
|
FEV 0.5/1/2/3: forced expiratory volume in 0.5/1/2/3 second, FVC: forced vital capacity, VC IN: inspiratory vital capacity, VC EX: expiratory vital capacity, VC max: maximum value of vital capacity, MEF 25/50/75: maximum expiratory flow rate at 25 %/50%/75% vital capacity, MVV: maximum ventilation volume
To exclude the interference from mixed factors in the relationship between pulmonary function and HGS, we further identified the correlation coefficients of other parameters with VC max, FEV3 and FVC (Table 5). As the data demonstrated, besides HGS, the following factors were also highly correlated with the pulmonary parameters: age, height, systolic blood pressure (SBP) and PP (ǀrǀ≥0.30 and p<0.01).
Table 5. Correlation coefficients (r) of variables with pulmonary function in males and females
Variables
|
VC max
|
FEV3
|
FVC
|
Males
|
Females
|
Males
|
Females
|
Males
|
Females
|
Handgrip strength
|
0.507
|
0.481
|
0.504
|
0.476
|
0.497
|
0.486
|
Age
|
-0.573
|
-0.604
|
-0.59
|
-0.605
|
-0.611
|
-0.614
|
Height
|
0.304
|
0.518
|
0.192
|
0.508
|
0.281
|
0.504
|
Weight
|
0.226
|
0.125
|
0.186
|
0.161
|
0.216
|
0.128
|
BMI
|
0.053
|
-0.065
|
0.083
|
-0.053
|
0.062
|
-0.055
|
Waist circumference
|
-0.017
|
-0.156
|
0.02
|
-0.185
|
-0.013
|
-0.155
|
Hip circumference
|
0.116
|
0.027
|
0.15
|
0.006
|
0.115
|
0.028
|
SBP
|
-0.182
|
-0.332
|
-0.118
|
-0.278
|
-0.186
|
-0.334
|
DBP
|
-0.044
|
-0.146
|
0.063
|
-0.117
|
-0.04
|
-0.136
|
PP
|
-0.294
|
-0.38
|
-0.231
|
0.325
|
-0.303
|
-0.385
|
Hb
|
0.24
|
0.017
|
0.303
|
0.03
|
0.263
|
0.016
|
Plasma glucose
|
-0.129
|
-0.201
|
-0.127
|
-0.319
|
0.135
|
-0.189
|
Albumin, g/L
|
0.125
|
0.087
|
0.144
|
0.089
|
0.148
|
0.114
|
Alanine aminotransferase
|
0.087
|
-0.020
|
0.192
|
-0.051
|
0.128
|
-0.005
|
Creatinine
|
-0.066
|
-0.104
|
0.009
|
0.019
|
-0.085
|
-0.114
|
TC
|
-0.014
|
-0.067
|
0.059
|
0.003
|
0.004
|
-0.043
|
HDL
|
-0.15
|
-0.005
|
-0.202
|
-0.016
|
-0.154
|
-0.015
|
The data shown in bold are variables with values of ǀrǀ> 0.30 and p < 0.01.
VC max: maximum value of vital capacity, FVC: forced vital capacity, FEV3: forced expiratory volume in 3 second;BMI: body mass index, SBP: systolic pressure, DBP: diastolic blood pressure, PP: pulse pressure, Hb: haemoglobin, TC: triglycerides, HDL: high-density lipoprotein
Next, we included age, height, SBP and PP in the multiple linear regression analysis to further study the impact of HGS on pulmonary function. The standardized coefficients of variables with parameters of pulmonary function are shown in Table 6.
In males, the standardized coefficients of HGS on FVC and VC max were 0.225 and 0.254, respectively. In the females, the standardized coefficients of HGS on FVC, VC max and FEV3 were 0.182, 0.175 and 0.194, respectively. These results illustrate that in the people with the same age, the greater the HGS he has, the better is the pulmonary function.
Table 6. The standardized coefficients of variates in the multiple linear regression analysis assessing the association between pulmonary parameters and handgrip strength
Standardized coefficients
|
VC max
|
FVC
|
FEV3
|
Male
|
|
|
|
Age
|
-0.396
|
-0.449
|
-0.464
|
Height
|
0.168
|
0.148
|
0.303
|
Handgrip strength
|
0.254
|
0.225
|
/
|
Pulse pressure
|
-0.134
|
-0.13
|
/
|
Female
|
|
|
|
Age
|
-0.393
|
-0.407
|
-0.447
|
Height
|
0.337
|
0.319
|
0.324
|
Handgrip strength
|
0.175
|
0.182
|
0.194
|
Pulse pressure
|
-0.101
|
-0.097
|
/
|
FVC: forced vital capacity, VC max: maximum value of vital capacity, FEV3: forced expiratory volume in 3 second, VC IN: inspiratory vital capacity