I made some notes from an article some time ago, (last winter I think). I can't remember where I got it from but it is a good explanation why muscles perform less well in the cold weather.
Here are the notes I took:-
At colder temperatures your muscles do not contract with the same intensity as they do in warmer temperatures. As the temperature gets colder your nervous system that transmits the impulses to move your muscles slows down. Since your muscle contractions are not as powerful as they are in warmer temperatures you slow down as a result. The cold can also reduce the blood flow to chilled areas of your body. Cold muscles can’t perform at the same level as a muscle that is warm.
The second reason for decreased pace is how your body uses energy at lower temperatures. As the temperature drops your body increases carbohydrate consumption as a source of fuel and reduces the reliance on fat consumption. As carbohydrates are an important source for energy for cycling you drain your reserves faster than you would at warmer temperatures. Your body also becomes less efficient in using oxygen as a fuel source resulting in more oxygen being used in cold conditions compared to the same effort in ideal conditions.
When cycling your body either operates in an aerobic or non aerobic state. In an aerobic state your body uses oxygen as a primary fuel source and it is very efficient in producing the energy needed for cycling.
When your pace is faster than your body can sustain aerobically your body taps the anaerobic system which does not use oxygen but instead breaks down carbohydrates to createlactic acid to fuel your cycling until a point is reached where the lactic acid build up slows your pace due to excess hydrogen byproducts.
As mentioned above your body consumes carbohydrates faster at lower temperatures which increases lactic acid production as a consequence. Since carbohydrates are burned faster at cold temperatures this increases the pace per mile that is sustainable at a given temperature. This is in addition to the disadvantage of having less efficient oxygen usage. In addition to your pace per mile being negatively impacted, there are other impacts to your performance when the temperature drops.
At lower temperatures your body has to work harder to maintain your core temperature. The result of this is more energy has to be expended simply for maintaining core temperature compared to ideal conditions or warm weather. This increased energy consumption comes at the expense of your cycling performance as less overall energy is available. Quite simply there are more demands for the same amount of available energy when it is cold.
When cycling in cold conditions it is important to keep your muscles warm and your core temperature maintained at all times. If you become chilled on a ride or allow yourself to cool down for any length of time your body is unable to get back to the prior temperature without returning to a warmer environment. As a result, your performance will suffer.
This is important when starting a ride. If you head into the cold and do not keep yourself warm and ready to go but allow yourself to cool down you will be at an even greater disadvantage that cannot be overcome. Allowing yourself to get to the point of shivering will quickly rob your body of energy as shivering is produced by your body engaging in the most inefficient muscle contractions it can to generate heat.
Hydration needs are impacted in colder conditions. When the temperature drops your blood pressure rises as your blood flow is constricted. To counter this your body removes excess water in the form of urine. In colder temperatures you do not sweat as much and your body does not trigger thirst the same way it does in warm conditions. As a result, it is very easy to become dehydrated.
Minimal intake of fluid can cause the feeling of needing to urinate, even if it is a small amount.The same rules apply for hydrating in cold weather as in warm weather:
I hope this will help in providing an explanation as to why your are slowing down in the cold weather.
