Dear Sarah,

Dear Susan,

The human body works best when it maintains a temperature of 37C and when exercise starts heating us up, the gland in our brain that controls our internal temperature (the hypothalamus) sends a message to nerve cells to contact the sweat glands. A sweat gland is a long, coiled, hollow tube that connects to our pores on the skin's outer surface. (Did you know our bodies have approximately 2.6 million sweat glands?) When these glands are stimulated, they secrete a fluid made of water, sodium, chloride and potassium. When this occurs your body has two options, depending on its environment.

Option One: If you are in a cool climate, the cells of your sweat glands reabsorb most of fluid, and very little sweat will reach the skin's surface. You may not break into a heavy sweat.

Option Two: If you are in a warm climate, the fluid reaches the skin's surface and runs off. The sweat evaporates cooling the body and leaving a salty residue on the skin's surface. If the air around you is hot and humid, your sweat will not evaporate and cool you off as quickly as it will if the air is hot and dry.

This residue left on your skin consists of sodium, chloride and potassium, which can cause dehydration, so it is important to drink plenty of fluids when you are sweating. Water with a bit of lemon juice will re-hydrate the body faster than water alone.

If you are not working up a good sweat on the treadmill, perhaps you are not working hard enough. To ensure that you are getting a good work, you want to be working in your cardio zone. To calculate your cardio zone, first find your maximum heart rate by subtracting your age from 220(e.g. 220- 35 = 185). Your cardio zone is between 60 - 86% of your maximum heart rate. Maximum heart rate 220 - 35 (age) = 185 beats per minute(b.p.m) Cardio zone: 185 (max heart rate) X 65% = 125 (b.p.m.

If working in this zone does not make you hot and sweaty, then consider the following:

• Am I dehydrated?
• Did I drink too many coffees today? (Coffee is very dehydrating.)
• Is the air around me cool? Is my sweat re-absorbed before reaching my skin's surface?
• Is the air around me very dry? Is my sweat evaporating so quickly so that I do not feel damp?

Sarah Brown is a very healthy woman. She is not only a fitness intructor at Goodlife where she teaches Body Pump, Body Flow and yoga but she is also a registered holistic nutritionist. If you have a question for Sarah, leave a comment below and she will try and help, but note that not all questions will be answered.