Is VO2 the fastest way to get "fit" in short term?

I'll come clean. I was recently challenged to a 5k by someone I know. The 5k is in 4 weeks. I'm already in okay shape, but want to throw in one workout per week to help me get into 5k fitness fastest. Thinking about throwing in 3x5:00 or 5x3:00 at 5k pace once a week.

You seem to be speculating that there is a quicker way to improve your 5K than to “‘correctly’ train” and for some reason think that “correctly” is not actually correct and therefore relegated to quotes.

There is absolutely faster ways to improve fitness, they just aren't as sustainable than training correctly. Like if I did something stupid long term I'd end up injured. How do you not understand the question I am posing?

I think a month is too little time to make any noticeable improvements with regards to vo2 max or aerobic capacity. you might detect some improvements in a laboratory test, but the adaptations would be very minimal within that time frame.

i think by far the easiest and best way to get faster within a month is to lose weight.

Now this is the outside the box thinking I'm looking for. Perfect. Time to lay off Taco Bell for a few weeks.

If you have a solid background in running, you can bounce back to decent fitness pretty quickly, especially if you've been running easy a few times per week and a casual workout here and there.

If I had to get someone as fast as possible in a month, staying within 25 mpw, I would have them do 3 workouts per week: 2 threshold/cruise interval workouts paired with 8-10x200m at mile pace with the last 2 at 95% max effort and 1 VO2max track workout (1k intervals or mile intervals w/ 1:1 work:rest).

After 2.5 weeks, I would also have them do a 1600m time trial all-out, jog around for 10 mins, and then do a 400 all-out.

2 days before the 5k, I would have them do 1x1600 at 3200m race pace, rest for 5 mins, and then do 1x800 at 1600m race pace.

Holy moly this sounds hard. Can't I just do VO2 every day?

The workout that will raise your aerobic capacity the quickest is HARD 200m reps.

^Just try it. Blast a 200m rep, then walk/stumble/jog around the track back to the start-point. Perform 12 reps.

^Over the following couple of days afterward, you will notice an improvement in aerobic capacity during your normal activities (e.g. while walking, climbing a flight of stairs, etc.)

But is this just for 5k and under? Not for 1/2 to full...

6x800m at 5000 goal pace or faster. Recovery: as little time as needed to be able to complete the workout at goal pace. Adjust on the fly

10x400 faster, again variable recovery

Running fast doesn't depend on just vo2max. You need to do it regularly so it gets easier by being a habit.

This was prescribed specifically for the conditions and desires defined by the OP. I think it will result in a short-term improvement in aerobic capacity, evidenced by a bit easier breathing (getting an extra air gulp) in normal activities over the following couple of days, more-so than a ‘VO2max workout’ like 4x4min w/3min recovery.

I like this. If you are a 25-mile a week easy run guy, I'll bet that your mental/physical feeling of "discomfort" trying to run really fast for 5k makes you slow down before your body might really need to. If a pace "feels" hard, you're more likely to drop off even if you might be able to handle it physically. Running at goal race pace gets you used to the feeling. Or how about 4 x 3:00 at 5k pace plus 2 x 1:00 at 3k pace and wind up with 1 x 1 min at mile pace for 15 minutes of work? It might make 5K pace feel less scary and more "endurable" for a longer period of time.

I would not run every day, i would include one rest day.

Skip the long run (now) and do 2 Q sessions/week as a race specific training.

Q, E, E, Q, E, E ,Rest

Just to be clear, you think the fastest way to get ready for a 5k in a month is by taking a day off each week?

The main answer on your question is,. intervals , both VO2max and threshold pace.

Read his post, Jan. Learn to read.

It's amazing how many people want to give advice to strangers so bad that they don't even read the posts they comment on

I like that. I've even done 4 x 1000 at 3k pace with equal time jog recovery. It's not ideal long term but you can get pretty fit quickly.

If no significant background in running, I'd say a 5k time trial once a week--hear me out: if you look at newbies at parkruns, they pb by 15s a week, every week, for like a month or two straight--maybe because they're getting fitter, but mostly because they're learning how to pace and how to mentally suffer through that 4th km.

Otherwise yeah 6-8 x 800 @ 5k will get you back in shape.

Then one other session of 5 x 1k at threshold and a few 200s. This should be an easy second session, focus on the time trial/VO2 intervals.

Whatever mileage you can handle to fill in the rest