Its funny what you start thinking about whilst out walking the dog! I was being taken for a walk by a particularly strong willed dog recently and started to get an aching in my shoulder and arm. I immediately started thinking about what I could do to avoid the pain and ensure it didn't cause any problems afterwards.
My advice (apart from having a well behaved dog) would be to regularly swap hands so the load is spread equally on the left and right. Be conscious of pulling the shoulders back into a neutral, comfortable position. Try not to keep the arm bent constantly to avoid fatigue. When you're done, stretch out those pesky pectorals and biceps. Have a little look at the suggested stretches and let me know if you find them useful. Happy walking!
Click on this link for a lovely chest opening stretch. This taps into that funny stretching I do that some of you will be familiar with!
The pectoral muscles consist of pectoralis minor and pectoralis major. Now just to make it a bit more complicated, the pectoralis major can be divided into the upper, middle and lower fibres. Stay with me here! It therefore makes sense to stretch all of these fibres to get the maximum effect. This is a fab stretch that can be done in a doorway. Remember that no stretch should be painful, it means you've gone a little bit too far, pull back a bit and relax into the stretch. You can adapt this by straightening your arms, giving you a great bicep stretch at the same time!