What’s the best gradient for hill sprints?

What gradient should you use when running hill sprints? It’s a question that crops up a lot. And I don’t think there’s a clear answer to what (in theory) is quite a straight forward question.

While, I’ve covered many of the different types of hill training in other articles; one area that I’ve paid less attention to is the hill gradient.

Now, I’ve always recommended using a moderate to moderately/steep gradient for most hill repeats (typically in the region of 4-8%) and slightly steeper for hill sprints. But recently it got me thinking…is this really the best gradient range for hill running? And…does the optimum gradient change for different types of hill workouts?

This led me to take a closer look at some of my own hill running data. 

Specifically, I wanted to see how the hill gradient affected factors such as: 

  • Running Cadence – the number of steps per minute when running.
  • Running Power – the power generated when running, which gives a measure of work rate.
  • Ground contact time – essentially the length of time your foot is in contact with the ground. A shorter GCT is often linked to improved efficiency.
  • Leg spring stiffness (LSS) – a measure of the stiffness in your muscles and tendons. Greater LSS (to a point) can indicate improved running economy.

To take a closer look I used data from the Stryd footpod. And, I decided to take a look at 2 different types of hills:

In each case I compared flat terrain running with 3 different hill gradients. And with the 60 second hills I also included downhill running.

Finding the best hill gradients for strength and power

However, it soon became clear that whilst these running metrics were useful, they weren’t giving me the full picture that I was after. And they weren’t providing any new insights into the effectiveness of different hill gradients. In particular, I wanted to find which hill running gradients were best for developing strength and also power.

So, I decided to also take a look at two additional metrics:

  • Power per footstep
  • Power per second of ground contact time

Why I chose power per footstep

Firstly, I wanted a way to assess workrate, in a way that would give an indication of the strength training benefit of different hill gradients. 

Now, the Stryd footpod allows you to measure power, which provides a very good measure of workrate. 

The problem here, was that I wanted to be able to assess the power per footstep rather than just a blanket measure of power. 

So, why look at the power per footstep?…(well), this gives an insight into the workrate per foot strike, rather than the power produced over a given time (seconds, minutes etc). 

In doing this, it takes account of cadence and you can then see whether the power per foot strike changes as gradient changes. 

Put simply, this gives an indication of which hill gradient is best for developing strength. 

I view this as being a bit like knowing what weight your lifting with each rep in the gym. Except we’re looking at how much work you’re doing with each stride.

Think of it this way: 

Greater power per footstep = greater strength training benefit.

What about assessing hill gradients for power development…

Why I chose power per second of ground contact

Now, while force per step gives you insights into the strength benefits of different hills, it doesn’t tell you as much about whether a particular hill gradient is beneficial for power development. 

Why is that? Surely, power is power…right? 

Well, the thing is power relates to how quickly force is applied. And power per step doesn’t tell us how quickly power is applied – just how much. 

The solution here is to factor in ground contact time – a measure (in milliseconds) of how long your foot is in contact with the ground. 

By doing this you can then workout the power per second of ground contact.

To do this, you simply divide power per footstep by the GCT in seconds. For example: 

  • Power per step = 100w
  • GCT = 200ms = 0.2seconds
  • Power per step ÷ GCT = 100 ÷ 0.2 = 500w power per second of ground contact.

Ok, so that’s the technical side out the way, now let’s take a look at what I found.

We’ll start with hill sprints…

The effect of Gradient on hill sprints

So, for the hill sprints I compared four different gradients: 

  • 0%
  • 4%
  • 8-10%
  • ~15%

In each case these were run at my maximal intensity, with each lasting approximately 23-25secs duration. All the data was averaged over the final 15seconds of each rep for consistency. And for each gradient I completed 6-8 reps, with each gradient completed on separate days, and then I averaged the data for each gradient.

While, hill sprints are often run over slightly shorter durations (10-12seconds), the data would have just been too inconsistent to be beneficial, so these were extended to improve the accuracy.

Here’s my hill sprints data…

Gradients and Hill Sprints

So, what does this tell us about the best gradients for hill sprints?…

Firstly, there was a gradual decline in cadence as gradient increases. This might seem surprising, as you may have heard that cadence increases when you run up a gradient. 

Well, it does…but only when compared with running at the same speed on flat terrain – not when you run at the same intensity. There’s also wide individual variation in how cadence changes, both in relation to gradients and running speed/intensity.

Secondly, ground contact times increased with increasing gradient. This is not surprising since GCT is strongly linked to cadence: 

  • Faster cadence = faster GCT
  • Slower cadence = slower GCT

Thirdly, despite the fact that these were all run at maximum intensity – I was able to generate more power at the steeper inclines than at the flat or moderate gradients. So, for each gradient I was working at maximum intensity, but I was generating more power as the gradient increased.

Fourthly, leg spring stiffness increased as gradient increased.

And finally, both the power per step and the power per second of ground contact increased quite significantly with increasing gradient.

So, what can you take from this?

The first point to note is: “for me”, steeper gradients (8-10% and 15%) were far more effective for strength and power development. They were also better for developing leg spring stiffness.

Both the 8-10% incline and the 15% gradient provided similar benefits for power development, but the 15% incline seemed to provide additional benefits for strength development (greater force per step). 

On the other hand, the 8-10% hill sprints allowed a greater cadence than the 15% hills.

In summary:

  • Steeper hill sprints (8-10%) and (15-20%) were more effective for strength and power development than moderate gradients.
  • The 15% hills were better for strength and LSS, but offered no real advantage (in terms of power) over the 8-10% hills.
  • The 8-10% hill sprints served as a good compromise between strength, power, cadence and GCT.

One point to note: different gradients will work better for different runners, depending on individual factors such as cadence and GCT. 

Ok, so what about 60 second hills…

The effect of Gradient on 60 second hill repeats

So, for the 60 second hill repeats I compared four different gradients:

  • -5%,
  • 0%
  • 4-5%
  • 8-10%.  

In each case these were run at the highest intensity I could sustain for ~60secs duration.

Here’s my data…

So, what does this tell us about gradients for hill repeats?…

Firstly, everything was lower (except cadence) during downhill running. No surprise there.

As with the hill sprints, there was a gradual decline in cadence as gradient increased. 

There was also a gradual increase in GCT, Power and power per step as gradient increased. And as with the hill sprints, I was able to generate more power during the uphill running than on the equivalent effort on flat terrain.

LSS was also higher at the steeper (8-10% gradient) but there wasn’t much difference between the flat and moderate (4-5%) gradient.

Interestingly, unlike with hill sprints, the power per second of ground contact did not increase at either the moderate or steeper gradient, when compared with running on flat terrain.

So, what can you take from this?

While the power per step increased with increasing gradient, the power per second of ground contact showed no increase compared with running on flat terrain. 

This indicates that while the moderate and steeper gradients were beneficial (for me) for strength development, there didn’t appear to be any significant benefit in terms of power development

In other words: 

The 60 second hill repeats provided no real benefit, in terms of power development, over flat terrain running intervals.

The reason for this was likely due to the slower ground contact times when running the hill repeats, which meant that the power per second of ground contact didn’t increase. 

This shouldn’t be surprising, since power is best developed through short ‘maximal’ efforts. And as these hill repeats were 60seconds duration, they’re far less beneficial for power development than hill sprints.

In summary:

  • Short 60 second hills were beneficial for strength but less beneficial for power. 
  • Steeper hills were more effective, than moderate hills, for strength and LSS, but this was at the expense of cadence and a slower GCT.

Again, the benefits from different gradients will vary between different runners, depending on individual factors such as cadence and GCT.

Ok, so that’s my take on gradients for hill sprints and 60 second repeats. It’s not perfect and I’m making no claims to it’s transferability to every runner – after all we’re all different – but it does give a real world example of how gradient can affect hill running training.

And from this it’s allowed me to approach hill training differently. 

So, here’s my final take on this and how I use this with my training…

Hill sprints gradient summary:

  • Hill sprints are effective for both strength and power development, although the gradient appears to affect just how effective these are.
  • Ideally use a moderately/steep gradient for hill sprints (~8-10%) which should increase both the strength and power component.
  • To prioritise both strength and power opt for a slightly steeper gradient (>10%) – useful during key phases of training.
  • An 8-10% gradient serves as a good compromise for strength, power and cadence.

Hill repeats gradient summary:

  • Hill repeats lasting around 60 seconds are effective for strength development, but far less effective for power (compared with hill sprints).
  • Again, steeper gradients (8-10%) appeared to be more effective for strength development than moderate gradients. Although, the steeper gradients reduce cadence and increase ground contact time.

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