I am 5'5'' and 140 pounds. I usually wear medium, but based on previous reviews, I am wondering-- should I get a large?

My second questions is if this jacket is appropriate for winter aerobics. I am training for a marathon, and run a great deal outside in very cold conditions. Is this jacket breathable?

Thanks!

Tech Specs:

Material:

[Body] Synchilla polyester pile (78% recycled); [Lining] brushed polyester mesh; [Trim] Supplex nylon 

Fleece Weight:

Midweight 

Windproof:

Yes 

Pockets:

2 Hand 

Weight:

19.5oz (553g) 

Recommended Use:

Skiing, Nordic skiing, climbing, ice climbing, alpine climbing, camping, backpacking 

Manufacturer Warranty:

Lifetime 

Country of Origin:

Mexico