Athena Vale
Several studies have been conducted to determine whether there are ethnic differences in muscle mass and density between black and white people. One study found that black males had twice the width, thickness, and circumference of the psoas major muscle at the segmental levels from L1-L2 to L5-S1 when compared to white males. Other studies have found that black people have a greater bone mineral density and body protein content than white people, resulting in a greater fat-free body density. These findings suggest that there may be ethnic differences in muscle mass and density between black and white people, but more research is needed to confirm these results.
| Characteristics | Values |
|---|---|
| Density of lean body mass | Greater in Black people than in White people |
| Bone mineral content | 10-20% more in Black people than in White people of the same height |
| Bone mineral density | Greater in Black people |
| Body protein content | Greater in Black people |
| Subcutaneous fat distribution | Racial differences |
| Limb length relative to trunk | Racial differences |
| Psoas major muscle width, thickness, and circumference | Approximately twice as much in Black males than in White males |
| Psoas major muscle cross-sectional area | Four times greater in Black males than in White males |
| Psoas minor muscle presence | 9% of Black males, 87% of White males |
| Mechanical properties of iliopsoas tendon | Stiffer and more failure-resistant in African American males |
| Subjects | 12 Black male athletes and 13 White male athletes |
| Skeletal muscle | Negative association with age after 27 years for both men and women |
| Peak skeletal muscle | Higher in men than in women |
| Skeletal muscle negative association with age | Steeper in Hispanic males and African American females within each gender |
| Skeletal muscle | Higher values in African American males and females across the lifespan |
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What You'll Learn
Bone mineral density
Several studies have shown that bone mineral density is higher in Black people than in White people. Bone mineral density (BMD) is a reliable estimate of bone mass and is strongly correlated with bone strength. Low BMD is associated with an increased risk of fracture.
A 1997 study tested whether racial differences in bone density could be explained by differences in bone metabolism and lifestyle. The study involved 402 Black and White men and women, aged 25–36 years, from Northern California. Body composition (fat, lean, and bone mineral density) was measured using a Hologic-2000 dual-energy x-ray densitometer. The study found that bone density at all skeletal sites was statistically significantly greater in Black than in White subjects.
Another study compared 60 matched pairs of postmenopausal Black and White women. It found that bone mineral density was 1.2-7.3% higher for Black women than for White women. The study concluded that racial differences in bone mineral density are not accounted for by clinical or biochemical variables measured in early adulthood.
A further study, using data from the 2007–2008 National Health and Nutrition Examination Survey, investigated racial and ethnic differences in physical activity and bone density in a diverse sample of 2,819 adults aged 40 to 80. The study found that bone mineral density was higher in Black than in White participants.
Overall, these studies suggest that Black individuals have higher bone mineral density than White individuals, which may contribute to stronger bones and a lower risk of fractures.
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Skeletal muscle differences
While there is limited information available on the relationship between skeletal muscle and age in adults of different ethnicities, some studies have found that African Americans tend to have higher values of skeletal muscle mass across the lifespan.
One study found that the width, thickness, and circumference of the psoas major muscle at the segmental levels from L1-L2 to L5-S1 in black males were approximately twice those of white males. The psoas major muscle had a four times greater cross-sectional area in black males than in white males, and the psoas minor muscle was present in only 9% of black males compared to 87% of white males. These differences may have implications for hip flexor strength and the incidence of low back injuries between the two racial groups.
Another study found that African American males and females had higher values of skeletal muscle mass across the lifespan, while Asian females and Hispanic males had the smallest absolute skeletal muscle mass compared to other ethnic groups.
In terms of body composition, blacks have been found to have a greater bone mineral density and body protein content than whites, resulting in a greater fat-free body density. This means that formulas for calculating lean body mass from density in whites may overestimate the lean body mass and underestimate the fatness of blacks.
Overall, these findings suggest that there are ethnicity-related skeletal muscle differences, and that body composition should be interpreted according to both gender and ethnicity. Different standards for skeletal muscle may be applicable for multi-ethnic populations.
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Muscle EMG activity
During an EMG test, a small needle with an electrode is inserted into the muscle being tested. The needle typically stays in the muscle for one to two minutes, and the patient may be asked to relax or activate the muscle in specific ways, such as lifting or flexing a limb. The electrical activity of the muscle is measured and displayed on a machine, which helps healthcare providers analyse the readings and identify any abnormalities.
A healthy muscle exhibits no electrical activity during rest and only shows activity when it contracts. However, a damaged muscle or one that has lost nerve input may display abnormal electrical activity at rest, and its electrical activity during contraction may deviate from typical patterns.
EMG tests are useful for diagnosing various muscle and nerve disorders, including polymyositis, muscular dystrophy, and myasthenia gravis. It can also help determine the presence, location, and extent of injuries or diseases affecting the muscles and nerves.
It is important for patients to be aware of certain precautions before undergoing an EMG test. For example, creams and lotions should be avoided as they can affect the accuracy of the test. Additionally, patients taking blood-thinning medications should inform their healthcare providers, as these may increase the risk of bleeding after the test.
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Body composition
Research has shown that there are ethnic differences in body composition between Blacks and Whites. Specifically, Blacks have been found to have a greater bone mineral density, resulting in a higher density of lean body mass compared to Whites. This means that at the same height and weight, Blacks tend to have a denser body composition with more muscle and less fat than Whites.
For example, a study by Schutte et al. (1984) found that Black males had approximately twice the width, thickness, and circumference of certain muscle groups compared to White males. Additionally, Daniels et al. (1997) observed differences in mineral homeostasis, volumetric bone mass, and femoral neck axis length between Black and White South African women.
Ethnic differences in body composition can have important implications for health and fitness. For instance, the greater bone mineral density in Blacks may lead to an overestimation of lean body mass and an underestimation of fatness when using standard formulas derived from predominantly White samples. This can impact the definition and assessment of obesity in different ethnic groups.
Furthermore, ethnic variations in muscle morphology may influence athletic performance and injury risk. For example, the study by Hanson et al. (2017) suggested that differences in the psoas muscles between Blacks and Whites could affect hip flexor strength and the incidence of low back injuries in a race-specific manner.
In summary, body composition varies between individuals, and ethnicity is one factor that contributes to these differences. Blacks tend to have a greater bone mineral density and lean body mass than Whites, which can have implications for health assessments and athletic performance. Understanding these ethnic variations in body composition can help develop more accurate standards and guidelines for clinical practice and sports medicine.
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Muscle contractile properties
In the human body, muscle contraction is based on two variables: length and tension. While muscle shortening and contraction are distinct concepts, tension within a muscle can be adjusted without altering its length. For example, when holding a weight or a child, tension is created in the muscles without any change in length. Following muscle contraction, muscle relaxation occurs, where muscle fibres return to a low-tension state.
Cardiac muscle contraction, specifically, involves two types of cells: autorhythmic and contractile. Autorhythmic cells set the pace of contraction, while contractile cells, or cardiomyocytes, perform the actual contraction. The process of contraction is initiated by an action potential (AP) induced by pacemaker cells in the sinoatrial (SA) and atrioventricular (AV) nodes. This AP travels to the contractile cardiomyocytes through gap junctions, activating Ca channels in the T tubules and resulting in an influx of Ca ions.
The influx of Ca ions into the cardiomyocyte causes them to bind to cardiac troponin C, moving the troponin complex away from the actin-binding site. This movement frees actin, allowing it to bind to myosin and initiate contraction. Subsequently, intracellular Ca is removed by the sarcoplasmic reticulum (SR), reducing the concentration of intracellular Ca. This decrease in Ca concentration returns the troponin complex to its inhibiting position on the actin, ending contraction and relaxing the muscle.
The contractile process in skeletal muscles is influenced by calcium and calcium/calmodulin-dependent kinases. Additionally, muscle-specific transcription factors like myoD and myogenin may play a role in regulating genes related to fibre size and strength. However, their involvement in determining myosin heavy chain expression is less certain. Overall, the interaction between various signalling pathways and muscle responses to endurance exercise contributes to our understanding of muscle contractile properties.
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Frequently asked questions
Studies have shown that African Americans tend to have higher values of skeletal muscle mass across the lifespan.
A 2017 study found that the width, thickness, and circumference of the psoas major muscle at the segmental levels from L1-L2 to L5-S1 in black males were approximately twice those of white males.
Blacks have been found to have 10-20% more bone mineral content than whites of the same height.
Yes, factors such as age, gender, ethnicity, and body composition can also influence muscle size.
