This is not an answer to your question, but I have something useful to say for your situation, and it is too long for a comment.
Because of joint issues I've had to stop hard weight training
As you probably know, resistance training is your Nr. 1 ally against age-related sarcopenia. I suggest you don't give up in weight training, which of course you haven't done yet (hence the adjective strong in your sentence). But for other readers in your situation, I would like to suggest the following tips:
Work out twice a week at most
Forget about working out on a M,X,F or similar schedule. Over the age of 50 you can build muscle but the optimum frequency is TWICE A WEEK (Stadler, Stubbs, and Vukovich 1997; Westcott and Guy 1996; Westcott et al. 2009)
Ignore all bodybuilding routines you read about
They are meant for much younger people, and most times they are designed with the aim of exhausting them and make them feel the need to buy supplements. When applied to older people they are a sure recipe for injuries. This does not mean that you cannot build muscle any more: every day a lot of people in their 70s and beyond recover from broken bones and torn tendon surgeries. In those cases, their bodies have the ability of putting on some bone and muscle mass. It is obvious that our bodies retain a certain ability to get stronger at advanced ages, but the workout patterns must change in some way.
Go easy on your joints by reducing weight but lower the execution speed so that you still target your soft tissues
Aged cartilage in your joints can be damaged by using too much weight. By lowering the weights you reduce that risk. But then you must focus on slow execution speed in order to trigger the growth signal within your muscles.
Do smart substitutions for shoulder exercises
Shoulders are a common concern above mid-age. The small and delicate rotator cuff muscles (responsible for placing the humerus head in the right position for each movement) usually have worn off or are weaken, which means that the humerus head will not be placed correctly in certain positions (specially overhead movements) and this will lead to soft tissue impingement. The coracromial ligament is often hypertrophied due to age wearing, reducing the subacromial space. This makes again certain overhead positions dangerous for the supraspinatus tendon and for the shoulder in general.
Therefore, you should avoid overhead presses and work out your shoulders by avoiding lifting your humerus above horizontal: do pushups and lateral raises instead. But be careful with lateral raises: do them with thumbs pointing up in order to avoid reducing the subacromial space, and do not move your arms strictly in the same plane, but advance your hands slightly to the front, the so-called "scapular plane elevations" by physical therapists. You can be sure they give a good workout to the lateral deltoid (Reinold et al. 2007) and not only to your supraspinatus.
Avoid overhead exercises in general
Not only for shoulder exercises as mentioned above, but also targeting other body parts. For instance, if for any reason you insist in doing triceps isolation exercises, choose Cable Pushdown instead of
Triceps Extension
Pay special attention to your Rotator Cuff
Slow external and internal rotations if done slowly, with light resistance and with emphasis on the eccentric movement will help your worn out rotator cuff tendons gaining health. Be very careful to include these exercises only at the end of your workouts (you don't want to exhaust those tiny but important muscles before doing the other exercises, because it is important that they assist the big exercises by positioning the humerus head correctly) and NEVER use a high resistance, because it is very easy to damage these muscles inadvertently.
Avoid bench pressing, do pushups instead
Avoid bench presses, where your scapulae and rear shoulder muscles are pressed against the bench, and do pushups instead. Not only they work out the same muscles, but they will contribute to your shoulder health by strengthening your shoulder girdle, serratus muscles and also by giving your core a gentle, isometric workout. If they are too easy for you, do them with a weighted vest. If they are too heavy for you, do them with your hands on a Smith machine bar whose elevation you can change in order to increase/decrease leverage.
Take care of your wrists by using push up handles and pull wrist straps for pull exercises (rows and similar)
Do not neglect those two accessories. Once you injure your wrists they take a very long time to heal.
Do NEVER work to failure. Choose a very slow linear progression instead
Start any exercise with a volume you can handle easily. Resist the urge to push through. In the next workout add no more than one rep per set. Do not change weight or leverage until you have achieved at least 15 repetition sets. This will ensure a very slow and safe progression. You may feel you are wasting time at the beginning but, as elementary logic dictates, you will sooner or later reach a training intensity that demands adaptation to your tissues, and you will have reached it slowly and safely.
Take special care on your knees
Unless you have been a life-long runner, choose swimming instead of running for cardio. A stationary bike is supposed to be OK too, but the ergonomics must be perfect and the progress should be carefully slow.
Take your time to warm up thoroughly
Do tons of shoulder circles and (empty hand) reverse flies before working out your upper body. Use the stationary bike for 8 to 10 minutes before squatting.
Do not push through exercises that give you joint discomfort. Choose surrogate exercises for them, or decrease range of motion
It is natural for instance that you feel joint pain at the most outstretched position of a chest fly. But by setting up the machine as to limit your range of motion, you can still work out.
Avoid isolation exercises if the muscles concerned are already at work within compound movements
For instance, by doing triceps isolation exercises you put your elbow joints under unnecessary stress. If you do pushups, your triceps are getting more than enough load to stimulate muscle growth and slow down or (partially) revert sarcopenia.
Stay away from too many crunches and abdominal work
Unless you have been doing them for years and your core is hard as iron, stay away from hard abdominal work, or you will be risking a hernia. During pushups your abs gets enough workout.
Do not hold your breath at all during resistance training
This may lead to dangerous blood pressure increase.
STOP IMMEDIATELY IF YOU FEEL DIZZY
And pay a visit to a cardiologist before engaging in sports at advanced age.
