A total of 98 participants, 55 males and 43 females, were included in this study. Among them, BMI was missing for one female, grip strength was missing for one male and one female. As is shown in Table 1, there were no significant differences in age and BMI between recruited men and women. For physical performance, including SPPB scores and TUG time, there were no significant differences between sexes, either.
Table 1
Age, BMI, SPPB scores, and TUG time of male and female participants in this study
|
Male
|
Female
|
P value
|
Age (y)
|
71.0 (65.0–78.0)
|
69.0 (67.0–74.0)
|
0.361
|
BMI (kg/m2)
|
22.9 (20.9–25.6)
|
22.8 (21.3–25.3)
|
0.721
|
SPPB scores
|
11.0 (10.0–12.0)
|
12.0 (11.0–12.0)
|
0.376
|
TUG time (s)
|
8.62 (7.25–9.92)
|
7.78 (7.37–9.47)
|
0.692
|
BMI: body mass index; SPPB: short physical performance battery; TUG: time-up-and-go-test |
For SWV-related results, there were no significant difference in either SWV (relaxed) or SWV (peak) between men and women. The peak strength of men was higher than that of women (P < 0.001), as a result, the ratios of SWV (peak) to peak strength were significantly higher in men (all P < 0.001). The details are listed in Table 2.
Table 2
Peak strength, SWV, and the ratios of SWV to peak strength of male and female participants in this study
|
Male
|
Female
|
P value
|
Peak strength (kg)
|
23.9 (17.8–29.1)
|
15.4 (11.8–18.5)
|
< 0.001
|
Cmax (relaxed, m/s)
|
3.0 (2.6–3.2)
|
3.0 (2.7–3.4)
|
0.141
|
Cmean (relaxed, m/s)
|
2.7 (2.3–2.8)
|
2.7 (2.4–2.9)
|
0.565
|
Cmin (relaxed, m/s)
|
2.3 (2.1–2.6)
|
2.4 (2.1–2.7)
|
0.339
|
Cmax (peak, m/s)
|
5.1 (4.4–5.6)
|
5.4 (4.7–5.9)
|
0.273
|
Cmean (peak, m/s)
|
4.3 (3.7–4.8)
|
4.6 (4.0-5.1)
|
0.244
|
Cmin (peak, m/s)
|
3.5 (3.0-4.2)
|
3.8 (3.3–4.2)
|
0.180
|
Cmax (peak)/ Peak strength (m/(s·kg))
|
0.204 (0.160–0.309)
|
0.365 (0.255–0.461)
|
< 0.001
|
Cmean (peak)/ Peak strength (m/(s·kg))
|
0.166 (0.134–0.273)
|
0.306 (0.203–0.398)
|
< 0.001
|
Cmin (peak)/ Peak strength (m/(s·kg))
|
0.139 (0.110–0.236)
|
0.245 (0.189–0.336)
|
< 0.001
|
Cmax, Cmin, and Cmean: maximum, min, and mean shear wave velocities |
The influence of age and BMI on SWV was limited in the recruited older adults. Only BMI was negatively correlated to Cmax (relaxed) (r=-0.381, P < 0.05), and the detail results are listed in Table S1. The correlations between SWV results and physical performance including SPPB and TUG results are shown in Fig. 2, and sex difference was observed in the correlation. Overall, the SPPB score was positively correlated to peak strength (r = 0.284, P < 0.01), and negatively correlated to Cmin (r=-0.235, P < 0.01) and the ratios of SWV (peak) to peak strength (r=-0.273, -0.264, and − 0.290 for Cmax, Cmean, and Cmin, respectively, all P < 0.01). The TUG time was negatively correlated to peak strength (r=-0.252, P < 0.05), and positively correlated to Cmin (r = 0.206, P < 0.05) and the ratios of SWV (peak) to peak strength (r = 0.323, 0.307, and 0.310 for Cmax, Cmean, and Cmin, respectively, all P < 0.01). No significant correlation was found between SWV (relaxed) and physical performance in men and women. For men, the SWV (peak) was negatively correlated to SPPB scores (r=-0.351, -0.355, and − 0.448 for Cmax, Cmean, and Cmin, respectively, all P < 0.01), and positively correlated to TUG time (r = 0.314 for Cmax, P < 0.05; r = 0.299 for Cmean, P < 0.05; and r = 0.369 for Cmin, P < 0.01, respectively). However, for women, the SWV (peak) was not correlated to SPPB scores or TUG time. The ratios of SWV (peak) to peak strength were significantly negatively correlated to SPPB scores (r=-0.511, -0.501, and − 0.532 for Cmax, Cmean, and Cmin, respectively, all P < 0.01), and positively correlated to TUG time (r = 0.462, 0.424, and 0.452 for Cmax, Cmean, and Cmin, respectively, all P < 0.01) in men. The ratios showed a similar trend in women but were only statistically significant in some correlations with the TUG time (r = 0.312 for Cmax and 0.310 for Cmean, both P < 0.05).
To further verify the clinical significance of the ratios, we divided these participants into different groups according the SPPB scores or TUG time, and the comparison in the ratios between groups are shown in Table S2 and Fig. 3. The difference between groups was consistent with the trend of correlation analysis. For men, the group with decreased physical performance had higher ratios of SWV (peak) to peak strength (all P < 0.01), which suggested the peak SWV of flexor digitorum superficialis reached higher in participants with decreased physical performance under the same output level of grip strength. And for women, the group with decreased physical performance also had significant higher ratios of SWV (peak) to peak strength (all P < 0.05).