Despite this pleasant surprise, I've decided to change my routine as I've been following it for a while. I'm hoping that in doing so, I may be able to make more progress in areas where I've been struggling for months.
On the advice of a friend who has caught the gym bug and has made some fantastic progress, I've decided to try Erin Stern's Elite 4 week plan from bodybuilding.com.  Today was my first session with the new routine and I very much enjoyed it. Day one is shoulders and arms  and it contained a number of exercises which I'd never performed before:
Though I'm used to doing seated shoulder presses with dumbbells, I'd never used my legs to augment the exercise. I managed to do the first five reps at 35kg but found that on the second set, my lower back couldn't handle the same weight again. I therefore dropped it down to 30kg.
Cable Rear Delts Flyes
These were great fun and I managed to complete four sets at 5kg. I'll definitely go higher next week.
Front Cable Raises
I'm used to doing dumbbell raises but there was something about the cable variation which made them more difficult. I have a long standing right shoulder injury which may have inhibited the exercise further. Though I have managed 12.5kg front raises in the past, I only managed 2.5kg on the cables.
The drag curl appears to place more stress on the forearms than the regular curl so I found this quite difficult. I started off at 20kg but dropped it to 15kg when I was struggled to complete the full 10 reps.
Plank to pull up and diamond push ups
I'd never performed either of these exercises and I struggled to complete even one rep of each so I decided to replace them with a cable row and close grip bench press. My cable row is also rather poor and given the lower back weakness I experienced in the Push Jerk, it's definitely something I need to try and address.
This was another exercise that I couldn't complete, again it appears because my back is too weak.
I'm looking forward to trying new exercises tomorrow. Wish me luck; it's leg day!