During the New Zealand winter the weather can often change quickly - so when you set off for your run or ride make sure you are dressed for success because ultimately it's your performance that will be the cost of poor clothing choices.
The mornings and evenings are generally cooler in most parts of the country, so individuals exercising should really have the majority of skin surfaces with at least one layer - but ultimately two or three is probably better especially for cyclists.
UNDERSTANDING HOW THE BODY REACTS TO COLD
"Within certain limits, the body is designed to adapt in cold temperatures. For example, muscles contract, which causes shivering, to distribute heat when you get cold. In very cold temperatures or prolonged exposure to cold, body temperature drops quickly and blood vessels at the surface of the skin on the face / head, arms, and legs begin contracting and pushing blood toward the trunk (or core) — a physiologic process that prevents additional heat loss through the skin and protects the vital organs from getting too cold. As soon as you warm up again, blood begins flowing back to your limbs."https://www.summitmedicalgroup.com/news/fitness/Exercising-Safely-in-Cold-Weather/
There are two things that your clothing has to do in the cold
- Take sweat away from the body
- Prevent too much body heat escaping from the body
So for the tough guys/gals that want to wear shorts and t-shirts running or leave the arm warmers or leg warmers off when they are on the bike then you really are setting yourself up for failure in your training sessions. If you want the body to function efficiently and perform then being at a warm temperature will have your muscles working at their best throughout the session.
And even though it's colder you still need to hydrate properly and filling up before you go doesn't really help due to cold diuresis (which is the need to pee all the time)
When you are cold your body reduces the circulation to the extremities and skin surface, a process called peripheral vasoconstriction (peripheral = at the edges, vaso = blood vessels) so concentrating a greater volume of blood in the body core. This increases the arterial blood pressure. The body's response is to try to reduce this pressure, the kidneys reduce the volume of circulating blood by removing water which is lost as urine. This process is known as "cold diuresis". On return to a warmer environment, circulation is restored to the periphery which reduces the overall volume which can trigger a thirst sensation, you drink, go outside in the cold again.. etc. etc. http://www.coolantarctica.com/Antarctica%20fact%20file/science/cold-weather-health.php#cold_diuresis
WHEN YOU ARE FINISHED
Make sure you have something warm to put on when you stop if you're not going to be able to get indoors. If you are stopping mid-ride or run then a light weight jacket or merino hat can be a great option to have in your back pocket (bike) or tied around your waist (running). Layers of gold!
COACHES QUICK SUMMARY
By keeping warm you are keeping blood circulating the body and all muscle groups. This will aid with performance as those key muscles have an easily available source of blood supply. This warm muscle with good blood flow will perform better for you and is less likely to be injured compared to cold muscles - due to the reduced blood flow around the muscles.