Possible explanations as to why a runner would get slower rather than faster over time while training?

Sleep is what I can think of. When I even lose a few hours of sleep in a week I start performing terrible workouts and feeling worn out all the time.

What do you do the rest of the days? A long run at MP is hard. What are your workouts?

If you feel worse it is IMO tired muscles. If you have not trained too long like that, you should get fresh in a couple of days if you go very easy (just 20-30min very easy, maybe 2-3 strides). Do you do recovery runs? What is the milage?

My guess is you are pounding your easy days harder than you should. Weekly long run at current marathon pace is also bonkers. Hopefully you mean a small section of it or some broken segments.

Post a week of training with paces and you might get better feedback.

You're probably running too fast. Cutting out the workouts is a good idea, but you might also leave your watch at home on a few runs per week.

Mad Maxx wrote:

I'm in my early 30s and set a goal for 2021 to run my first marathon in the fall.

. Anyway, I've been training, and rather than getting faster over the last month, it seems I keep getting slower and feel worse on my runs.

If you've only been training for a month... or only training at these higher levels for a month... you're simply not fit enough yet to handle these workouts and you're not recovering enough to do the next workout so you are gradually tearing yourself down.

You could try training by HRM, especially to stay below the top of your recovery zone on your easy days. Or you could just back off your current paces for a while. You need to be thinking Base and building mileage now. The marathon pace long runs can come later.

You ran in HS and college so you probably think you know a lot about running, but the marathon is a different animal.

Don't wing it. Find a coach, or just follow Pfitzingers book so you'll have some guidance.

Long run at MP is too hard if you are also doing two speed sessions during the week. Run a solid pace for your long run, but if you are going to do MP during a long run, skip one of the two workouts during the week.

Usual culprits for runner fatigue are thyroid issues and iron deficiency. If you do not see any improvement by managing pace on long runs better, you may need to get some blood work done.

Overwork, either excessive volume or intensity

I call this swatting flies w/ a sledgehammer

Training not addressing the needs of the athlete

Where is the limitation? Speed side or strength side?

Intensity x volume dynamic can add muscle mass to certain athletes

FT often hypertrophy after initial adaptation period

ST will not always benefit from additional work or certain types of quality.

High inflammation diet

Insufficient calories to support the work

Insufficient sleep to get the growth hormone spike

Well you are not 20 anymore.

You have not done anything for 10 years, so it will take a little bit to build up again. My guess is that you think you are a lot fitter than you actually are. Maybe reduce your training a bit and do a 10k and a HM race and see where you are at.

Just because you think you can run a 2:40 Marathon does not mean you have the potential right now to run a 2:40 Marathon.

Be patient and enjoy the process.

Very easy to overtrain in the marathon. All of the advice given above is accurate. I recommend sticking to a 2Q approach in your training as, IMHO, 2 workouts and a long run in marathon training is a bit much. Better to alternate the following workouts/long runs on the weekends:

Weekend 1 - Long run with 10-12 miles at MP with perhaps a single mile at T pace.

Weekend 2 - Long run with a tempo in the beginning, easy miles in the middle, and a tempo at the end where the objective is to run at the same pace as the first tempo. Great for teaching you to run strong on tired legs.

Weekend 3 - Steady long run. Nothing fast. Just time on feet.

For the midweek workouts:

Midweek 1 - long warmup followed by 5x1000i

Midweek 2 - 4x2T or some variation

Midweek 3 - Shorter version of an MP effort or a progression run

Every third or fourth week should be a cutback week when your weekly mileage is concerned.

Take a look at the 2Q plans in Daniels Running Formula. His plans roughly follow what I wrote above. Pfitz is also a good resource as another commenter mentioned.

You gotta run your easy days EASY. Find some friends to make those runs talk/joke sessions to ensure conversational pace. Sleep is also key. Don't forget your nutrition and hydration. Marathon training is brutal, and you body needs the fuel and recovery to succeed.

I’d recommend blood work to check things like ferritin, CBC with differential, B12, Vit D, and minerals. I remember when I first started training for the marathon and increased the volume I plateaued for a while. It turned out my ferritin was low-normal. You break down red blood cells through footstrike hemolysis.

If you’re running in the early morning your Vit D may be low too- something a lot of runners may not realize. Most runners likely need extra iron, electrolytes, and minerals, esp with temps warming up. A good sports drink and protein post runs can help with the recovery.

Also echo what others said about overtraining. You don’t need a long run every week or for it to be hard. Work with how you feel in the present- don’t force yourself to do workouts or long runs if you’re not feeling well rested.