I'm not 40 yet but approaching. I actually had a roof fall almost a year ago and it caused an injury on my right side.. from my leg up to my shoulder, elbow and hands. sprained my elbow badly, mild separation.
it has led me to lose workouts because the inflammation. now a stupid person would take an A-inflammatory and go in there and pound away. but those are the guys who end up with chronic injuries. you really have to listen to your body and back off. I haven't been able to lift heavy but i am gradually coming back.
so to answer your question shit happens in life that will effect your workouts. the best thing you can do is listen to your body and train SMART.