Time in the saddle with a heart rate between 70% - 80% of your maximum HR is what experienced cyclist advise newbie’s like me. However, keeping a high cadence 90-100 at the same time is very tiresome and painful what prevents me to do long rides.

Considering that I started (road) cycling 2 weeks ago (28 years 151 pounds), would long low cadence rides or short high cadence rides benefit me at this point?

Rule #1: Do not trust advice from "experienced athletes"... Get smart yourself: Get a good book on training I would say. Joe Friel's Cyclist Training Bible is a good one: It is written for newbie's just as well as for pro's.

70-80% of HR max could be too intense for you to begin with. Besides that: Well trained people reach their AT (Anaerobic Threshold) at a higher HR, so 80% could be a "ride in the red zone" for one rider, while it is perfectly manageable for another.

I would try to increase cadence at lower intensity in long, slow endurance rides first. Once you build up a good endurance base and the muscle memory to spin at high cadences efficiently, you will find that you can hold that cadence at a higher intensity too.

It does not make much sense to try to learn tired muscles to spin efficiently: Your pedaling will get sloppy and this gets you nowhere. Just concentrate on high cadence at an intensity that keeps your legs fresh. They will learn much faster and you will be able to hold that cadence at a higher intensity sooner.

JK's words are spot on IMO...

Books I would recommend are:
The Cyclist's Training Bible (Cycling) - Joe Friel
The Heart Rate Monitor Book for Cyclists - Sally Edwards, Sally Reed
Serious Cycling - Edmund R. Burke

JK's point I most agree with and would highlight is
"I would try to increase cadence at lower intensity in long, slow endurance rides first. Once you build up a good endurance base and the muscle memory to spin at high cadences efficiently, you will find that you can hold that cadence at a higher intensity too."

building a base fitness is common advice within books written by well respected cycling coaches.

_________________
"Ride it like you've just stolen it!"

So it boils down to this: Maintain a high cadence, but bring down the intesity.

By the way, I have the "The Lance Armstrong Performance Program: Seven Weeks to the Perfect Ride" book. What do you think if this book?

First, cadence of 90-100 is not high cadence it is normal cadence, Second, get a book.

My advice to newbies is to spend a fixed amount of time in the saddle 6 days a week, I like 45 minutes. Your improvement will correllate most strongly to your consistency and yes do in general keep your cadence up at around 90-95 rpm.

If you have started cycling 2 weeks ago, any type of riding will benefit you. You will experience a day to day improvement over some months, then you will reach a plateau, in my opinion, you should start serious training when you reach this plateau, till then just enjoy the rides, ride at the cadence that you like most. Once you are fit, it's the time to experiment with low/high cadences etc.

I didn't like this book.

ok and 6/10 would be my feedback.

I prefered other books my the likes of Ed Burke.

_________________
"Ride it like you've just stolen it!"

There are far better books out there, Friel, Burke are both good.

I pretty much agree with everyone, except also concentrate on the motion of the pedaling. Make it smooth, push and pull, making a circle. This will help with efficiency and allows you to get to a higher cadence and keep it there. this smoothness will also come with time.

Enjoy, welcome to cycling.

I am using PC Coach by Edmund Burke and 50% of the workouts it has me doing are in the 110 to 130 rpm range and zone 2 heart rate. This is for a recreational rider who wants to get faster. The program as several levels and I recommend you don't over state your abilities. Some of the workouts can get really hard.

if you have only been cycling two weeks take it steady and enjoy it the fitness will come then you can start with more serious training like cadence and hours in the saddle