My appeal to authority: I am currently 51, and have been training year round (minus injury time, which was basically one year of Achilles rehab) since I was 4. I currently train in martial arts, run, and chase my toddlers around. :)
There aren't, really, other than knowing that the older you get the harder it is to put on muscle (Since you are fighting against the age related losses), and that inflammation and other stresses build up a little quicker. Most of the articles touting the dangers are aimed at the person that arrived at 40 out of shape and never really having worked out in their life (or tried it and failed.)
This is a great article on the 40+ approach (he calls it a scam), and some of the realities. I will quote some of the specifics, but it is a long article (These are titles with a informational blurb after each one):
Train more frequently but with shorter workouts.
Avoid grinding reps, especially with heavy barbell work.
Use variations of the patient lifter’s method (i.e., 8 sets of 3 crisp reps with your 5RM).
Manage volume correctly.
Always bookend very intense or high volume phases with a deloading phase.
If you like gadgets and data, investigate HRV.
Steady state cardio is an awesome recovery tool.
Also in the same article under lifestyle:
Get more sleep.
Manage overwhelm. Find a way, some way.
Talk to someone.
Read more books and less blogs
So instead of training "off and on", make it more of a priority. Pay attention to sleep and nutrition, and you'll be happy and healthy when you hit 60+ My personal list looks as follows:
- Get sleep. Aim for 7+ hours a day, preferably all in one go.
- Hydrate. When I feel my worst, I usually find I have not been drinking enough liquids.
- Nutrition. Eat at least 80% healthy, and take a multivitamin to cover your bases.
- Take a day off. Listen to your body, and know the difference between "I just don't wanna" and "I really need a day". Knowing yourself is the biggest key to avoiding injury/overtraining. This also means that if you start a workout and it's just flat with no hope of getting better, bag it. Go see a movie. Or feed ducks in the park. Whatever.