Chapter 4 Relationship between the index of muscle cross-sectional area
muscles (biceps brachii and brachialis) and C of upper arm were determined by ultrasonography and a measuring tape, respectively. The F of elbow flexor muscles was calculated by dividing the TQ during the elbow joint flexion by the forearm length (the distance from the head of radius to the processus styloideus) of each subject. Using them, the relationships between MT×C determined at rest and during MVC and F were examined.
Subjects
Fifty-eight middle-aged and elderly men (n=22) and women (n=36) aged 51-77 yr volunteered as subjects. Their means (±SDs) in age, body height and body mass were 64.8 (±6.9) yr, 158.5 (±7.9) cm and 56.4 (±9.6) kg, respectively. Thirty-three of the subjects participated in an organized Taijiquan program for one and half hours at least once a week. The remainders were physically active to a moderate degree or sedentary. All of the subjects were functionally independent in daily living. Overall, the activity level was comparable over the ages. All measurements were performed for the subjects’ right arms. They had no orthopedic abnormality in their right arms. This study was approved by the Ethical Committee of the Faculty of Sport Sciences of Waseda University and was consistent with their requirement for human experimentation. Each subject was informed of the purpose and procedures of this study and possible risks of the measurements beforehand. Written informed consent was obtained from each subject.
Procedures
The MT, SAT and C were determined at the level of 60% of the upper arm length as described in the Chapter 3. In the measurements of the upper arm length and the forearm length, the elbow joint was kept in an extended position. After they were measured in 0.5 cm with a steel tape, the level of 60% of the upper arm length was marked with a pen. A B-mode ultrasonic
apparatus (SSD-1000, Aloka, Japan) was used for the MT and SAT of anterior upper arm measurements. An electronic linear array probe (UST-579T, 7.5 MHz wave frequency, Aloka, Japan) was prepared with water-soluble transmission gel and applied on the anterior skin surface.
The obtained ultrasonographic images were printed out by an echo copier (SSZ-309, Aloka, Japan). The MT was determined as the distance from the adipose tissue-muscle interface to the muscle-bone interface. The SAT was determined as the distance from the skin to the adipose tissue-muscle interface. Each of them was measured in 0.05 cm. The C was measured in 0.1 cm with a cloth tape.
The measurements of MT, SAT and C were performed while the subjects seated on a test chair and their right arms were secured to a torque meter (VTE-002R, VINE, Japan) by using an unelastic belt. The subjects kept 90° of shoulder joint flexion angle and elbow joint angle, and their wrists were fixed in a position halfway between supination and pronation. First, the measurements of MTr, SATr and Cr were performed. Second, MTm, SATm and Cm were determined, in which the subjects performed MVC of isometric elbow joint flexion for 3 seconds.
The TQ data measured during the elbow joint flexion was amplified by a strain amplifier (DPM-611B, Kyowa, Japan). Afterward, they were transmitted through an A/D converter (PowerLab/16SP, ADInstruments, Australia) into a personal computer (LaVie LL350/8, NEC, Japan) at 100 Hz sampling frequency and processed with a low-pass filter (cutoff frequency: 20 Hz). The TQ measurements were performed two times with at least a 5 min interval. If the difference between two values of TQ was more than 10% of the higher one, the TQ was measured one more time. In two or three TQ measurements, the highest value was adopted. The MT and SAT were measured on the first trial and the C was measured on the second one. In the case of the third trial, the MT and SAT or C was measured once again according to the following conditions. If the first measured torque was lower, the MT and SAT were measured on the third trial. If the second measured torque was lower, the C was measured on the third trial. The MT,
SAT and C were measured while torque output peaked and was stable. The reproducibility of MT and C were ensured in the Chapter 3.
Statistical Analyses
Descriptive data are presented as means ± SDs. A Student’s paired t-test was used to test the differences in MT, SAT, C and MT×C between at rest and during MVC. Pearson's product-moment correlation coefficients were calculated between MT×C both at rest and during MVC and F. According to a prior report (Cohen and Cohen 1983), the difference in these correlation coefficients were tested.
For the elbow flexor muscles, there is no significant difference in the CSA-strength relationship between the sexes (Ikai and Fukunaga 1968, Kanehisa et al. 1994a, Miller et al.
1993). In the present study, too, the slopes and the intercepts of the linear regression line for the relationships between MT×C both at rest and during MVC and F were not significantly different between men and women. Hence, the present results were analyzed without distinction of sex.
Statistical significance was set at P < 0.05.
4-3. Results
Descriptive data on MT, SAT, C and MT×C at rest and during MVC are shown in Table 4-1. Each of MT, C and MT×C during MVC was significantly higher than that at rest (P < 0.001).
The SATm was significantly lower than SATr (P < 0.001).
The F was significantly correlated with each of MTr×Cr (r = 0.778, P < 0.001) and MTm×Cm (r = 0.905, P < 0.001) (Figure 4-1). There was also a significant difference between these correlation coefficients (P < 0.001).
4-4. Discussion
In the MVC measurements, MT×C increased and SAT decreased from those at rest (Table 4-1). These results suggest an increase in the CSA of contractile component relative to the muscle CSA index at the measurement site and so it would be a reason that F is more closely related to MT×C during MVC than that at rest. Thus, MTm×Cm appears to be more appropriate to assess the relationship between muscle CSA index and strength and correspondingly the muscle strength per size for middle-aged and elderly individuals compared with MTr×Cr.
Moreover, the correlation coefficient between MTm×Cm and F was significantly higher than that between MTr×Cr and F (Figure 4-1). This differs from the finding in the Chapter 3 that examined in young adults, in which the corresponding difference was not statistically significant.
As described in the earlier part, the proportion of the noncontractile tissues within a muscle compartment for elderly individuals is greater than that for young adults (Kent-Braun et al. 2000, Klein et al. 2001, Rice et al. 1990) and the arm skin and subcutaneous tissue volume increases with aging (Rice et al. 1989, 1990). The MT and C include not only contractile component but also noncontractile component. Furthermore, C includes not only elbow flexor muscles but also such tissues as skin and subcutaneous adipose tissue. Therefore, it is suggested that the accuracy of MTr×Cr for middle-age and elderly individuals is lower than that for young adults, and correspondingly that the difference between the accuracy of MT×C during MVC and that at rest for middle-age and elderly individuals is greater compared with young adults.
To examine this possibility, the relationships between the product of thickness and circumference and the CSA for elbow flexor muscles both at rest and during 30%MVC in nine older men (57-74 yr) were tested in the same way as used in the Chapter 2 (Figure 2-1). Then, the relationships in older men were compared with those in younger men described in the Chapter 2. In older men, the correlation coefficient between the product of thickness and circumference and the CSA at rest was significantly lower than that during 30%MVC (P < 0.01)
(Figure 4-2). By contrast, the corresponding difference was not statistically significant in younger men. These results suggest that the accuracy of MT×C for middle-aged and elderly individuals is lower at rest than during MVC. In middle-aged and elderly individuals, therefore, the correlation coefficient between MTm×Cm and F would be significantly higher than that between MTr×Cr and F.
4-5. Summary
The correlation coefficient between MTm×Cm and F was significantly higher than that between MTr×Cr and F in middle-aged and elderly individuals. As described in the Chapter 3, the corresponding difference was not statistically significant in young adults. Therefore, the muscle CSA index determined by ultrasonography and/or a measuring tape during maximal isometric contraction appears to be more appropriate to examine the relationship between muscle CSA index and strength, especially in middle-aged and elderly individuals.
y = 2.47x - 61.2 r = 0.905 (P < 0.001) y = 2.76x - 31.5
r = 0.778 (P < 0.001)
0 200 400
0 100 200
MT×C (cm2)
F (N)
rest MVC
Figure 4-1 Relationships between MT×C at rest and during MVC and F (n=58). MT, muscle thickness; C, circumference; MVC, maximal voluntary contraction; F, muscle strength. The correlation coefficient during MVC was significantly higher than that at rest (P < 0.001).
y = 0.269x - 15.1 r = 0.843 (P < 0.01) y = 0.141x + 4.01
r = 0.636 (P = 0.066)
0 10 20 30
0 50 100 150
product of Thickness and Circumference (cm2) CSA (cm2 )
rest 30%MVC
Figure 4-2 Relationships between the product of thickness and circumference and the CSA for elbow flexor muscles at rest and during 30%MVC in older men (n = 9). CSA, cross-sectional area; MVC, maximal voluntary contraction.
Table 4-1 Descriptive data on MT, SAT, C and MT×C at rest and during MVC (n = 58).
***
***
***
***
rest MVC
MT cm 2.6 ± 0.4 3.3 ± 0.5 SAT cm 0.31 ± 0.12 0.26 ± 0.11
C cm 27.2 ± 2.5 27.8 ± 2.5 MT×C cm
271 ± 15 91 ± 20
Variables
Values are mean ± SD. MT, muscle thickness; SAT, subcutaneous adipose tissue thickness; C, circumference; MVC, maximal voluntary contraction. *** Significant difference between at rest and during MVC, P < 0.001.