So often when I have slower runners attend my Thursday sessions they're surprised when I explain at the start that their session will be tougher than for the guys at the front of the group.
They've seen the pre-session blurb (72 minutes alternating 6 minutes at MP, 6 minutes at MP + 30 seconds) and wonder why they're not doing that. The reason is that they would find this pace too easy and finish the session feeling like they hadn't really done a proper session.
This is a great example of the slower runners paradox - that slower runners generally run faster than fast runners.
The Slower Runners Paradox
Where you plot up the average training and long run pace against race pace (I found a great graph of this once but am really struggling to find it - please shout if you see it in the comments!) as a precentage of race pace slower runners run considerably faster than elite runners.
When I take my guys who are planning to run in the 2:45 region and put them through the "simulator" workout (16 miles at race pace (no faster) in full kit and shoes they will wear on race day and using their nutrition strategy ) they find it a difficult session despite them being able in 2 weeks time post taper to do the race at that pace. By contrast if you take a 10 minute mile marathoner and put them through the same session it'll probably be slower than their weekly long run!
There's a couple of reasons for this but the main ones are:-
+Faster runners generally tend to be doing a higher weekly mileage and are often training in a semi-fatigued state.
+Whilst faster and slower runners are covering the same distance on the day in terms of how your body deals with the intensity is very different if you're competing in a 5 hour race to a 2 hour race.
For this reason slower (but not novice) runners would probably get more out of following a elite ultra runners schedule where they are training for a 5 hour race than an elite marathoners schedule which is more like a half marathon training plan for them.
Adapting Time Based Sessions
So where slower runners train at MP + 30s for them that is probably closer to their 6 or 7 hour race pace and will feel like a dawdle. By contrast the 2:45 guys at MP +30 are running at probably closer to a 4 hour notional race pace
Slower runners thereby need to adapt training sessions and schedules to ensure they're training at the appropriate intensity. Far too many slower or novice schedules back off and reduce the intensity compared to the faster schedules when in reality slower runners can cope significantly better and for longer durations at 5k/10k/HM and Marathon pace (which is probably more like the steady pace for faster runners).
As an example if I prescribed 4 x 10 minutes at 10k pace off a minute recovery they would probably revolt en masse half way through the third rep. Runners with a 60 minute 10k PB by contrast would find this a relatively easier/standard session.
Distance Based Sessions
This applies for distance based sessions as well but with a slight tweak - here it may be necessary to reduce the distance you are running. If you have a group doing 800s which varies from people finishing them in 2:30 to 5 minutes then you have people training at very different intensities.
Those running them in 2:30 (with say a notional 5k PB of 16 minutes) will be training at fairly close to their VO2 max pace (say 95%), By contrast those finishing them in 5 minutes will be training significantly slower than their VO2 max pace and will not experience the same benefits.
These runners will need to instead run a shorter duration rep (say 400) and considerably faster - at more like their notional 3km or even 2km race pace and take the same recovery length.
By the end of the session they will have clocked the same duration of running at the same intensity as the faster runner and see the same benefits rather than have run considerably further (increasing injury risk) at an intensity which doesn't really match the purpose of the session.