For my aged/damaged body itís my lower back that canít handle Deadlifting and Squatting back-to-back if I do anything in the way of reps.
As far as the number of reps you do if you havenít already I would check out Prilepinís Table:
This gives a history of how it was developed and one method of applying it:
This attempts to expand it for use by bodybuilders rather than strength athletes: http://www.t-nation.com/readArticle.do?id=4677737
Use this calculator to estimate your 1 rep maxes if you donít want to take the time or risk actually testing them.http://www.exrx.net/Calculators/OneRepMax.html
The advantage to following the total rep guidelines of the table is that it ensures you get enough reps to have a positive training effect without doing more reps than necessary thus needlessly tiring yourself.
By following these rep guidelines and other training principles Iíve found Iíve been able to jumpstart my Squats and Deadlifts which were stagnant for some time at around 265 lbs. and 315 lbs. respectively until last March, and are now both at 390 lbs. and still climbing.
Something else Iím religious about is that I never do Deadlifts for reps as IMO that is one of the best possible ways you can screw up your back. No rep after the first one, and often not even the first one (about 70% of realistic 1RM attempt failures are due to technique, 20% a sticking point and 10% mental), is going to be perfect. Instead I set a number of reps as a target based on prilepinís table and do a series of singles.
Iím a stoneís throw away from 52 so believe me Iíve researched all the best ways I can find achieve the optimal balance between muscle and or strength gains and fatigue management. Myo-reps is another very effective method but geared more toward bodybuilding.