Increasing LT threshold - how long does it take?

I've a 5K at the end of April and a HM mid May - looking for any advice on the best way to increase my pace reasonably.

38, 5"11", 83Kg/13st1 (from 14st11 early last year), running for 3 years (2-3 months of each year only) and started again properly in Feb) completed 4 HM, 1 FM races

Training currently only 3-4 times/week with no other excercise, ~25-30 miles (just recently ramped up to this and plan to go slowly higher), LSR up at 9-12 miles at 9:15-9:30 conversational pace. Hilly HM race last week with PB of 1:45, last month 10K PB of 47:48 and I just had my LT measured (as a byproduct of taking part in a sports science trial at work) and it started rising between 12 km/h and 13 km/h (only did 1 km/h increases for 3 min each from 9-15 km/h) I imagine around 7:45 pace.  Main aim Berlin Marathon at the end of Sept.

I have real trouble running any faster than 7:45 pace, and anything under 8:00 drifts up unless I really focus.

Assuming I try to train optimally to increase my LT, how long does this take?  2 months or 6 months to see a decent improvement?  I was thinking of P&D up to 55 miles plan starting after the May HM, with some variation on the RW Band 2 (1:25-1:50) HM plan leading up to the HM.

I'd hope to see a sub 1:40 HM by May and a sub 3:50 marathon as a realistic goal (is it? )

I've also got my eye the April 5K as I've not really raced one before (24:08 PB in training) and find that distance/speed unpleasant - I imagine upping my LT would help a lot here?

Any idea what is realistic in the short to medium term? Cheers.

Anyone any advice, I realise I'm probably a lot slower than most on here?  Any speculation on what I should aim for in the 5K in 5 weeks,  pace wise?

Hi Daeve

The impact of a new training stimulus depends on how well trained the targeted system already is. If you haven't been doing any stuff at LT then you could notice improvements within a couple of weeks.

As a real-life example, I've just come out of an 8-week training block designed to work LT and it's probably improved by about 15-20 seconds/mile (using heart rate as a guide). In the past I've found that continuing to focus training on a particular system beyond a couple of months sees diminishing returns (maintenance sessions are still required of course).

Focusing on LT will definitely help your 5k time. Of course, there is more specific training you can do for a 5k (Vo2 max), but the effects will be less than optimal - and probably even negative in the longer term - unless your base mileage is sufficient and your LT has been attended to.

And be wary of increasing mileage and adding quality at the same time.

i'm going to make a few assumptions about your current fitness based on the info you provided, but i reckon that improving your aerobic endurance by increasing your training volume, instead of focusing on speed work or tempo runs, would yield the best results at the moment.

View it as a long term commitment, rather than just getting you in shape for your next race. Gradually add in a few more miles per week, around 10% is a ballpark to avoid overuse injuries. The first thing that will improve is your cardiovascular fitness, then your muscles, then your connective tissue strength, which you'll need to avoid injury. One reason a lot of people get running injuries is that they become "fit enough" to run more than their legs can handle. Be patient and your body will become strong enough to take the extra miles. There is a good thread on here called "HADD training", search for it, and those guys wil give you some good tips. Don't expect overnight results, but if you can train consistently you'll get faster, I guarantee it.

I'm not sure how muscular you are, but at 5'11'' you could probably do with continuing the weight loss a bit too. Sounds like you've made great progress over the last year, but just shifting any excess fat will nudge up the pace too. Don't focus on this as a goal though, if you gradually increase the mileage and eat well, it'll be a welcome side-effect to your training.

Cheers - input gratefully received.  Your assumptions are probably correct, I was up at 50+ miles a week back in August and Sept last year for the marathon but let it slide until Feb this year after completion.  I'm fairly lucky/robust and dont get injured really, so I went from nothing and my first week was 36 miles this year with no issues (couple of 12 milers in there) but all easy miles.