Transition from marathon to sub 20min 5k

I've recently done a marathon and want to start training for a sub 20min parkrun 5k (with occasional 10k race).

My marathon didn't go to plan (4h 07min at Brathay Windermere) but in the weeks before it I ran pbs of 1h 34min 34sec for a half and 20min 19sec for a 5k.

I'm trying to devise a 5k training plan but am confused by many sources. I'd welcome some feedback - I'm most confused about exactly what my hard sessions should be (interval lengths, pace, recovery time etc.) My current plan looks like:

Mon: Rest

Tue: Session or Easy (4-6 miles)

Wed: Easy (4-6)

Thu: Session or Easy (4-6)

Fri: Easy (4-6)

Sat: Race 5k/10k or Easy (4-6)

Sun: Race 5k/10k or Long (6-10)

with one or two sessions/race per week depending on how my legs feel. I also plan to swim 2-3 times a week and start cycling but am aware that won't impact my 5k much.

My main questions are: Does this look sensible and what sessions (interval lengths / pace / recovery) would you recommend?

Thanks a lot for any help.

I would try and get in one good interval session a week. Start off with a decent warm up, at least a 10 minute jog and some light stretching and strides to loosen out. Usually we base the main set on a fixed time or distance like 90 seconds or 400m a little quicker than your 5k pace, then jog for 90 seconds for recovery. Start with say 6 sets and build up to 10 over a few weeks. I would do a 10 minute jog to cool down as well though i'm not sure how important this really is.. also make sure to allow an easy day, such as a light swim, after a tough interval session.

This is one of my favourite sets, you can build up the number of reps over time:

2x5mins at 80% effort (roughly 5k pace) then 3x2mins at 90% effort (out of breath). 90 seconds between all of the reps.

You obviously have a good level of fitness behind you so speed work is probably the main focus.

Thanks for the advice - I'll try out the sessions you suggested!

Since there's a parkrun near me I can do a 5k race any Saturday I choose. Would it make sense to do intervals on Tuesday then 5k race on Saturday or should I just do one of the two each week?

I'd do both sessions every week and don't add any more hard sessions. I TRY not to go to a parkrun looking to race it every week. Easier said than done The interval session should probably be your main session most weeks. Maybe pick a parkrun 3 weeks in advance and decide to race that one and take the interval session a little easier that week.

I think Tuesday and Saturday is well spread out. Just train according to how you feel. I would never do an interval session unless i'm feeling 100%. I'd go for a cycle or swim instead. And I would say that cycling does have a positive effect on running in regards to strength and leg speed so don't feel like you're wasting time.

Thanks for that. So, to summarise, my week could look something like the following?

Mon: Rest

Tue: 6-10 x 90 sec slightly faster than 5k pace with 90 sec recoveries. (4-6 miles)

Wed, Thu, Fri: Easy (4-6).

Sat: 2 x 5 min 5k pace and 3 x 2 min slightly faster with 90 sec recoveries (4-6) most weeks. 5k race occasionally.

Sun: Long run (6-10).

I would probably swim Mon/Wed/Fri depending on motivation.

Sounds good but 2 hard interval sessions in a week will be tough. Make sure not to overdo it. Maybe do the parkrun every week and take it easy enough. If the intervals are going well you could step up to twice a week but once is probably enough. Just to be clear, when i said I'd do both sessions, I meant one interval on tuesdays and the parkrun on saturdays, but don't feel the need to go flat out in the parkruns every week. Good luck. I'm sure you'll be well under 20 in no time.

Thanks for the help I'll follow your advice - hopefully I will consistently break 20 mins before the summer ends

here are my thoughts which assume a good endurance base (which youhave) http://the5krunner.com/2011/08/22/5k-sub-20-minute-5k-running-and-training-plan/

your plan seems too easy if you want to improve quickly. x training is good

i would go as far as saying don't waste your time with ANY easy runs (zone 1 HR)