Abstract
[Purpose] This study aimed to clarify the utility of maximum calf circumference by analyzing its relationship with body composition and whole-body endurance in healthy young Japanese males. [Participants and Methods] This cross-sectional exploratory study included 30 healthy young male participants, aged 19.1 ± 0.3 years. Maximum calf circumference was measured using a measuring tape, and body composition was measured using a bioimpedance device. Oxygen uptake and heart rate were measured during a multistage continuous treadmill test, and maximum oxygen uptake was estimated by calculating a linear regression equation based on the relationship between heart rate and oxygen uptake. Associations between maximum calf circumference and maximum oxygen uptake adjusted for body composition values were examined using Pearson’s product-moment correlation analysis. [Results] Maximum calf circumference showed moderately to highly significant positive correlations with all body composition parameters (body mass index, skeletal muscle mass, fat free mass, body fat mass, and phase angle). Maximum oxygen uptake per fat mass showed moderately significant negative correlations with maximum calf circumference. [Conclusion] These findings indicate that maximum calf circumference may serve as a useful potential index for checking normal-weight obesity in young males considered healthy based on body mass index.
Key words: Maximum calf circumference, Normal-weight obesity, Maximum oxygen uptake
INTRODUCTION
The maximum calf circumference (MCC) is simple, convenient, accessible, and easy to measure. The MCC is better than the body mass index (BMI) or waist circumference in reflecting muscle loss in the lower extremities with aging or decreased physical activity. In some studies, MCC has been reported as an important indicator of malnutrition, skeletal muscle mass, and sarcopenia, and has been widely studied, especially among older adults1,2,3,4,5). Although the importance of maintaining and improving MCC in older adults has been emphasized, it is necessary to examine whether the significance of MCC in healthy young people is the same as that in older adults.
Although MCC is a valuable health indicator, its relationship with oxygen uptake as an index related to whole-body endurance is unclear.
Maximum oxygen uptake is a widely recognized indicator used to assess endurance capacity. To account for individual differences in body size, maximum oxygen uptake is usually normalized by dividing it by body mass. Recent advancements in bioelectrical impedance analysis (BIA) have simplified body composition measurements, making this information more accessible. Consequently, there is a need to examine the relationship between MCC and maximum oxygen uptake, not only relative to body mass but also using values adjusted for fat-free, skeletal muscle, and fat mass. Oxygen uptake should be examined from a new perspective that accounts for body composition parameters.
This study aimed to clarify the utility of MCC by examining its relationship with body composition and whole-body endurance, adjusted for various body composition values in healthy young Japanese males. Analyzing muscle and fat mass in relation to whole-body endurance in healthy young individuals may provide insights into peripheral factors, such as muscle quality and metabolic involvement. In particular, the existence of normal-weight obesity (NWO) has been pointed out as a health risk6). Exploring this relationship using MCC is valuable, as it represents a simple and practical measure.
PARTICIPANTS AND METHODS
This cross-sectional exploratory study included 30 healthy young male participants with no history of systematic athletic training, aged 19.1 ± 0.3 years. The exclusion criteria were orthopedic prosthesis and any clinical condition or medication usage known to affect the maximum oxygen uptake.
All assessments were conducted at the Exercise Laboratories of the Faculty of Physical Therapy, International University of Health and Welfare, Odawara campus, between May and June 2025. The study protocol was approved by the Ethics Committee of the International University of Health and Welfare (Approval No. 24-TA-127), and conducted in accordance with the Declaration of Helsinki.
Calf circumferences were measured using a measuring tape and recorded to the nearest 0.1 cm. The greatest circumference of both lower legs was measured. Because the inter- and intra-examiner reliability of the MCC measurements were high7), the measurements were performed once in the supine position.
BIA was performed using the InBody 380 body composition analyzer (InBody Co., Ltd., Seoul, Korea). Measurements were performed at least 2 hours after food ingestion. The participants were assessed in the standing position following a period of rest. Body composition assessment included the phase angle (PhA), skeletal muscle mass, and body fat. Whole-body PhA was derived from resistance and reactance values obtained at a frequency of 50 kHz.
Oxygen uptake and heart rate (HR) were measured using a multi-stage continuous treadmill test. The protocol consisted of eight stages. Each lasting three minutes. Participants walked at a constant speed of 3.5 km/h with slopes of 0, 5, 10, and 15%. These conditions were repeated with additional weight: 1 kg distributed in four pockets on torso clothing, plus 1 kg on each wrist and 2 kg on each ankle (10 kg). Oxygen uptake was measured breath by breath using an exhaled gas analyzer (AEROMINITOR AE-310S, Minato Medical Sciences Co., Ltd., Tokyo, Japan), and HR was monitored using via electrocardiogram (WEP-1200, Nihon Kohden Co., Ltd., Tokyo, Japan). Data from the last minute of each stage was used for analysis. A linear regression equation was established to describe the relationship between HR and oxygen uptake. Maximum oxygen uptake was estimated by extrapolating the regression line to predict the maximum HR, calculated as 220-age. The regression model demonstrated strong validity for all participants, with correlation coefficients (r) ≥0.90 and coefficient of determination (R2) ≥0.81.
MCC and body composition were measured on the same day, oxygen uptake was measured on a different day, and the equipment was operated by a different physical therapist. Measurements were conducted for each participant between 9:30 and 11:30 with the order of assessments randomized. No results were shared among examiners until all data collection was complete.
BIA and oxygen uptake results are presented as means and standard deviations. Pearson’s product-moment correlation analysis was performed to examine the associations among MCC, body compositions, and estimated maximum oxygen uptake adjusted for various body composition values. All statistical analyses were performed using IBM SPSS for Windows version 25 (IBM Corp., Armonk, NY, USA), with the significance level set at 5%.
RESULTS
Data on MCC, body composition, and estimated maximum oxygen uptake adjusted for various body composition values are summarized in Table 1. The MCC was approximately 36 cm on both sides.
Table 1. Body composition characteristics and estimated VO2max expressed as mean ± standard deviation.
| Males (n=30) | |
| Age (years) | 19.1 ± 0.3 |
| Right calf circumference (cm) | 35.7 ± 1.9 |
| Left calf circumference (cm) | 35.9 ± 1.8 |
| Height (cm) | 172.6 ± 4.8 |
| Body mass (kg) | 63.3 ± 6.5 |
| Body mass index (kg/m2) | 21.3 ± 2.5 |
| %Body fat (%) | 15.6 ± 4.1 |
| Fat mass (kg) | 10.3 ± 3.2 |
| Fat free mass (kg) | 53.3 ± 4.8 |
| Skeletal muscle mass (kg) | 30.1 ± 3.0 |
| Phase angle (°) | 6.4 ± 0.5 |
| Estimated VO2max (mL/min) | 2,794 ± 511 |
| Estimated VO2max/Body mass (mL/min∙kg) | 44.3 ± 7.5 |
| Estimated VO2max/Skeletal muscle mass (mL/min∙kg) | 93.1 ± 15.0 |
| Estimated VO2max/Fat free mass (mL/min∙kg) | 52.5 ± 8.5 |
| Estimated VO2max/Fat mass (mL/min∙kg) | 310.1 ± 122.8 |
Simple correlations among MCC, body composition, and estimated maximum oxygen uptake, adjusted for various body composition values, are shown in Table 2. The MCC showed moderate to highly significant positive correlations with all body composition parameters. Furthermore, MCC showed a moderately significant negative correlation with estimated VO2max/fat mass.
Table 2. Correlations between calf circumference and measured variable (n=30).
| Right calf circumference | Left calf circumference | |
| Body mass index (kg/m2) | 0.867** | 0.908** |
| Skeletal muscle mass (kg) | 0.671** | 0.701** |
| Fat free mass (kg) | 0.674** | 0.701** |
| Body fat mass (kg) | 0.668** | 0.714** |
| Phase angle (°) | 0.491** | 0.541** |
| Estimated VO2max (mL/min) | 0.374* | 0.318 |
| Estimated VO2max/Body mass (mL/min∙kg) | −0.026 | −0.101 |
| Estimated VO2max/Skeletal muscle mass (mL/min∙kg) | −0.023 | −0.115 |
| Estimated VO2max/Fat free mass (mL/min∙kg) | 0.021 | −0.067 |
| Estimated VO2max/Fat mass(ml/min∙kg) | −0.412* | −0.459* |
*p<0.05, **p<0.01.
DISCUSSION
This study examined the relationship among MCC, body composition values, and oxygen uptake as an index of whole-body endurance adjusted for various body compositions in healthy young males. The BMI of the study participants was 21.3 ± 2.5 kg/m2, which was within the normal range. Nishida et al.8) examined body composition in healthy male students with an average age of 19.7 ± 1.1 years, BMI of 21.1 ± 2.6 kg/m2, and reported that the MCC was 36.9 ± 2.6 cm. In comparison with these findings, the measurements of the participants in this study were close and therefore can be interpreted as being within the normative range.
The MCC is an indicator that shows a strong correlation with body mass index (BMI) and body composition values not only in older adults1, 9) but also in healthy young males.
This study is the first to report a significant negative correlation between the MCC and maximal oxygen uptake per fat mass. BMI alone may not accurately identify all obesity cases, especially in people with NWO10). The index of maximal oxygen uptake per fat mass indicates that, if participants have a standard BMI and similar maximal oxygen uptake, the amount of fat reflects the overall endurance capacity of the body. In other words, high fat mass in the NWO state correlates with decreased whole-body endurance and increased MCC, suggesting physical fitness and behavioral health concerns. Therefore, measuring the MCC may be a valuable new index for checking NWO in young males who are considered healthy in terms of BMI. Although there is a tendency to believe that a larger MCC is desirable, given concerns about frailty and locomotive syndrome even among young people, a negative correlation in the opposite direction, which may be a sign of reduced whole-body endurance when adjusted for fat mass, can be interpreted as a notable new finding.
This study had several limitations. First, this was a cross-sectional, exploratory study, and further research is needed to examine the longitudinal changes in fat mass and MCC associated with sports training. Second, the participants were only male; hence, the results cannot be generalized to healthy young individuals. NWO in children and unbalanced eating habits and extreme dieting in young females are gaining focus11, 12), and further research with a wider range of participants is needed. However, because it is challenging to recruit children and young females who are assumed to present with NWO, we first conducted an exploratory analysis using healthy young male participants. Third, the study only analyzed body composition; biochemical findings should also be included as outcomes for further detailed analyses.
Conflict of interest
The authors declare no conflict of interest in this work.
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