BIA：評估您身體組成的方法
由於 BIA 有助於區分體脂肪、肌肉與體內水分在身體組織中的分佈方式，它被廣泛用於測定身體組成。 當脂肪相對於精瘦體重過多時，稱為「身體組成異常」。雖然許多人只關注體重，但身體組成異常已知會增加罹患多種疾病的風險，包括心血管疾病、第二型糖尿病及高血壓。 因此，BIA 可以是評估您健康狀況的重要工具。以下是您應了解的 BIA 方法、歷史、準確性及潛在偏差相關知識。
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什麼是生物電阻抗分析？
生物電阻抗分析（BIA），又稱生物阻抗，是測量生物組織對低電壓電流流動所產生阻抗的方法。
人體由不同類型的組織所組成，這些組織具有不同程度的導電性。在約 70 微安培（μA）的電壓下，電流主要會通過導電性較強的組織，例如水分或肌肉。
透過測量源極與接收電極之間的電壓降，BIA 可確定這些組織對電流通過所產生的阻抗程度。
這種「阻抗」即阻抗值（Z），等於與組織接觸的兩點之間所測得的電壓（V），與施加於該組織的電流強度（I）之比值。
阻抗計算公式為 Z=V/I。
A four-electrode configuration for BIA between the right arm and right leg.
生物電阻抗分析的起源為何？
Although the first electrical impedance tests date back to Georg Simon Ohm (1788-1854), its application to the human body and the measurement of biological tissues was theorized in the second half of the 20th century.
In 1962, in a paper entitled "Bioelectric properties of tissue. Impedance measurement in clinical medicine". Significance of curves obtained, the French physician Thomasset first introduced a method using two electrodes, comparing two current frequencies to allow any doctor to calculate lean body mass and obtain a satisfactory estimate of a patient’s nutritional status.
With time and a growing interest in body composition, other methods emerged. In 1994, the National Institutes of Health (NIH) agreed on a technology assessment, whose purpose was to "provide physicians with a responsible assessment of bioelectrical impedance analysis (BIA) technology for body composition measurement (source).
How does bioelectrical impedance analysis indicate body composition?
Bioelectrical impedance analysis is now widely used in the medical field to distinguish the amount of body water, body fat and skeletal muscle in a body.
The analysis first obtains total body water (TBW). This is the amount of fluid that can be found inside and outside your body cells. For an adult, total body water represents 45 to 60% of total body weight.
The other components—with more insulating properties such as body fat or skin—will be more “resistant,” meaning that they conduct electricity less effectively.
Using ratios of bioelectrical impedance measured at a separate frequency, complex equations then estimate the amount of fat-free mass within the body. The amount of body fat is finally deducted from the total weight.
Beyond body composition
Note: Bioelectrical impedance is also a method used in cardiology to assess pulse wave velocity, another biomarker that determines the stiffness of the arteries to infer cardiovascular health.
脂肪組織中測得的阻抗
In fatty tissue, the resistance (or impedance, or "Z") is high, and measured current flow (V) is low.
去脂組織中測得的阻抗
In muscles or water, there is less opposition to the current flow, so the measured current (V) is higher and impedance is low.
生物電阻抗分析的準確度如何？
The signal used in bioelectrical impedance analysis is totally safe and painless for both adults and children, but note that bioelectrical impedance is not recommended for people with pacemakers.
On one hand, many scientific publications attest to the reliability, precision and accuracy of the BIA method in providing valid estimates of total body water in individuals.
On the other hand, there is still a need for standardization and consensus on certain factors that may alter the test results. Some of these factors are described in a study published in The American Journal of Clinical Nutrition entitled “Clinical characteristics influencing bioelectrical impedance analysis measurements.”
探索更多指標：
可能影響 BIA 分析的因素包括：
環境
Changes in the skin temperature due to the environment where the measurement is taken are thought to impact skin surface impedance, as detailed in a science paper published in the Journal of Applied Physiology: "Controlled ambient and skin temperatures should be included in the standardization of BIA measurements."
水分補充
由於肌肉主要由水分組成，脫水會降低體液與電解質的含量，進而降低這些組織的導電性。因此，去脂體重更可能被低估。水分補充程度在一天中變化很大，這也說明了為何保持一致性是準確進行 BIA 估算的重要因素。
年齡
A 2017 study published in the Journal of Bodywork and Movement Therapies, "Body composition estimation in children and adolescents by bioelectrical impedance analysis: A systematic review", demonstrated a perfect correlation between BIA-based body composition estimation in children with reference methods. However, fat-free mass is still often underestimated in children.
重度肥胖
Because the equations that interpret the fat-free mass based on total body water results rely on reference population segments, the body composition estimate might be inaccurate for people considered to be overfat. A study entitled “Evaluation of visceral fat in massive obesity” indicated that an “underestimation of fat mass in obese subjects, and the error becomes greater with increasing BMI.”
金屬植入物
配戴金屬植入物的人可能會得到偏低的體脂肪數值。然而，這個數值會隨時間保持穩定，因此他們仍可成功追蹤自身身體組成的變化。
BIA 裝置有哪些不同類型？
多年來，為了以更高的精準度和便利性測量生物電阻抗，業界設計了許多不同的裝置。這些裝置使用相同的測量方法，主要差異在於電極數量，以及直接測量的身體部位與估算的身體部位。
除了裝置設計之外，演算法的性質與複雜程度也至關重要，這些演算法用於根據接收到的頻率估算全身水分與去脂體重。科學家在建立這些演算法時，會採用可能有所不同的體脂肪標準。
使用智慧型體重計測量身體組成，若能保持一致的測量狀態，有助於可靠且具成本效益地追蹤身體組成的變化。
BIA 體重計
這類體重計能將電流從一條腿向上傳導，再從另一條腿向下傳導。使用前，使用者須輸入年齡、身高與性別。
手持式 BIA 裝置
又稱手對手阻抗裝置，用於測量手臂及上軀幹的生物阻抗。
全身阻抗裝置
這類常見的 BIA 裝置由四個電極組成，每個電極分別放置於身體的左側或右側，將電流從手臂穿過身體傳導至腿部。
DSM-BIA
直接分段多頻率 BIA（DSM-BIA）是最先進、也是最昂貴的生物電阻抗分析裝置。此裝置將身體分為 5 個部分，並分別獨立測量每個部分的阻抗。
生物電阻抗分析（BIA）仍是一種快速且安全的成人身體組成估算方法。正因如此，這種具成本效益的替代方案被廣泛應用於臨床、運動醫學及其他健康相關領域。目前仍有許多研究尚未就統一標準達成共識，以協助修正使用 BIA 方法時殘存的解讀偏差問題。然而，保持測量的一致性有助於準確偵測數值變化，讓任何人都能輕鬆追蹤身體組成的變化。
探索我們的智慧型體重計：
Body Scan 黑色
HK$3,980.00 HKD
促銷價
HK$3,980.00 HKD
定價
終極健康檢查。更長壽的生活。
Body Comp 白色
HK$1,831.00 HKD
促銷價
HK$1,831.00 HKD
定價
為您的身體提供最先進的全面檢測。
Body Smart 黑色
HK$1,035.00 HKD
促銷價
HK$1,035.00 HKD
定價
達成目標的強效健康檢測。
Body Scan 白色
HK$3,980.00 HKD
促銷價
HK$3,980.00 HKD
定價
終極健康檢查。延長壽命。
Body Comp 黑色
HK$1,831.00 HKD
促銷價
HK$1,831.00 HKD
定價
為您的身體提供最先進的健康檢查。
Body Smart 白色
HK$1,035.00 HKD
促銷價
HK$1,035.00 HKD
定價
實現目標的強大健康檢測。