Muscle for generating heat loss from the hands

Cambridge biological anthropologists have shown that muscle mass is able to predict the rate of heat loss from the hands during severe cold exposure, while body mass, stature and fat mass do not. According to Stephanie Payne, lead author Hands have a large surface area-to-volume ratio, which can be a challenge to maintaining thermal balance in cold conditions.

We wanted to study the influence of body size and body composition on heat loss and rewarming in the hands to determine whether they affect hand temperature and dexterity in cold conditions. These results are important for understanding thermoregulation (the body's ability to regulate its temperature).

Volunteers from around Cambridge, including University students and local residents, took part in the study. After having their vital statistics taken and body composition analysed to measure the amount of fat and muscle, each volunteer plunged their hands into ice cold water for three minutes. The rate at which volunteers' hands heated up again was measured and recorded using a thermal imaging camera.

Volunteers were of European origin and aged between 18 and 50. Many populations across the globe have developed vasoregulatory adaptations to deal with severe cold. Some populations lose blood flow to the hands very quickly to make sure they retain their body heat internally, whilst others, for example the Inuit, have periodic pulses of blood to the hands to combat frostbite.

Being aware of the effects of body composition on how cold your hands get is crucial. For example, women and children are less likely to have a high muscle mass so cold-weather gear, such as gloves, should be produced and marketed with that in mind.
          haleplushearty.blogspot.com

Fat distribution increases the risk of heart attack

It's not the amount of fat in the body but where it's stored that may increase the risk for heart attack, stroke and diabetes. People of the same weight or body mass index (BMI) may have different risk profiles, based on genetics, lifestyle and diet. In addition, body composition differs between men and women, with women having proportionately more fat and men having more muscle mass.

Fat distribution is an important determinant of cardiometabolic risk.  There are different body shapes, common descriptors of human body shapes, based on where fat tends to be stored in the body. In apple-shaped bodies, fat is distributed largely around the midsection, while in pear-shaped bodies, fat is distributed lower around the hips and thighs. The type of fat stored also plays a role in cardiometabolic risk. One type of fat-ectopic fat-is dangerous. It may be found in places such as the abdominal region, muscles, liver and other organs.

There are gender-based differences in body composition and ectopic fat depots and that these could be associated with gender-specific risk profiles for diseases like diabetes, heart disease and stroke, researchers examined overweight and obese men and women wit the same BMI who were otherwise healthy. After fasting overnight, the study participants underwent dual-energy x-ray absorptiometry (DXA) and CT scans to determine body composition, as well as magnetic resonance spectroscopy (MRS) for fat quantification and analysis.

The results showed that the women had a higher percentage of fat and more subcutaneous (below-the-skin) fat but lower lean mass, compared to men. However, men had more visceral adipose tissue (VAT), or ectopic fat depots located in the abdomen around the internal organs known as a "beer belly", and more ectopic fat in the muscles and liver. Obese men have relatively higher visceral fat, fat within muscle cells and liver fat, which are all risk factors for cardiometabolic disease, compared to women with the same BMI. However, men have higher muscle and lean mass, which are protective for cardiometabolic health.

Women have a higher relative amount of total body fat and higher superficial thigh fat, which is protective for cardiometabolic health. Compared to women, men had higher measures of cardiometabolic risk overall, but ectopic fat was not significantly associated with cardiometabolic risk in men. Ectopic fat in women, however, was strongly associated with cardiometabolic risk measures. The detrimental fat depots deep in the belly, muscles and liver are more damaging for cardiometabolic health in women compared to men.

The researchers looked at the relationship between sarcopenic obesity-or the loss of skeletal lean muscle mass in the presence of obesity and its relationship to cardiometabolic risk. Many factors can lead to sarcopenic obesity in young adults, particularly obesity and lack of exercise. Growth hormone helps to build muscle mass. Nutrition also plays an important role, and too little intake of protein can lead to muscle loss. The researchers studied  young, overweight and obese adults who were otherwise healthy.

Participants underwent DXA and CT scans and various metabolic tests. Results showed that having a lower lean muscle mass to BMI ratio was associated with cardiometabolic risk, and these effects were stronger in women than in men. Sarcopenic obesity may be an under-appreciated mechanism linking obesity to cardiometabolic disease.
          haleplushearty.blogspot.com