The first heart rate monitor was invented in 1977  by Seppo Säynäjäkangas, and the world was in awe. But Seppo’s invention only measured heart rate and nothing more. Fast-forward to 2015, and Garmin’s HRM-Run strap, together with a running or multisport watch, records your heart rate, plus 6 other variables. Not long ago you would have been wired up like a lab rat to get all these data measurements. Now all you do is press the stop button on your Garmin watch and the data is instantly available.

The HRM-Run strap measures cadence, stride length, vertical ratio, vertical oscillation, ground contact time balance and ground contact time. Each one tells a story about your running style and can help you become a better runner. When you finished reading this article, you will know what these measurements mean, how to interpret them and the value they can add to your running.

Cadence
Running cadence is measured in terms of how many times your feet hit the ground per minute (bpm). One question that gets asked a lot is what the perfect cadence is. Of course a “perfect cadence” does not exist. A benchmark of 180 bpm does exist, but cadence is determined by variables such as height, weight and your unique biomechanics. Your level of fitness also plays a part. If you strive to maintain a cadence that is unsuited or too demanding on your level of fitness, it can lead to fatigue or more seriously, an injury. Bolt, Gatlin and the pint-sized Shelly-Ann Fraser Price, all 100m sprinters, have respective cadences of 221, 231 and 286. Of course, they are extreme athletes and we should not compare ourselves with them, but it reflects height as a variable.

How can we, as everyday runners, use cadence measurement for the good? We all have a cadence that feels comfortable, but when fatigue and loss of form sets in, it becomes easier to sustain injuries. Reverting to a slow cadence, or a “plod” when fatigue sets in is not the answer. In terms of averages, research has shown that good runners stay between 180 and 200. That means your body will stay on top of your hips and you will not over-stride, meaning you will not force your body to play catch-up all the time. Weekend warriors fluctuate between 160-180, but anything lower than that is not ideal. Over-striding and straining other muscles to pull your body over your hips is bad running form and lead to injury.

Keeping your cadence the same, whether you are fresh or fatigued, is vital to sensible running. Rather shorten your stride length to keep your cadence up. The familiar “Comrades shuffle” that ultra-distance runners use, is an example of maintaining a good cadence.

Stride length
Stride length is the second most important factor that your HRM-RUN heart rate strap will measure. After all is said and done, speed = cadence frequency X stride length. The length of your stride is determined by your height and your body’s unique biomechanics.

That is why it is not easy to answer that frequently asked question: “What is optimal stride length?” Stride length is less of a fixed variable than what cadence is. Tall runners generally have longer stride lengths than shorter runners, but cadence frequency ultimately determines speed.

If your foot is under your hips when it touches the ground, you have a healthy stride length. Running disciplines also determine stride length. Sprinters have the longest stride, becoming shorter as distance increases. Terrain also determines stride length. Stride length in trail running is shorter in general due to all the climbing and stepping to negotiate technical tracks. If you want to get an idea of your average stride length, make sure you are well rested and run a 10Km road run in zone 3 with your Garmin run heart rate strap. That should give you a fair idea of your optimal stride length.

Vertical Ratio
Next up is the vertical ratio, and it is measured as a percentage. If your vertical ratio percentage is 8.2%, it means that of all your movements, 8.2% is “straight up” as opposed to forward. Of course running requires you to lift off the ground, but if your bounce, or vertical ratio, is excessively high, you use your energy to go in the wrong direction. In simple terms it means that you should not run like a gazelle.

Another fixed variable is that vertical ratio drops as speed increases, a longer stride length offsets the vertical ratio to a lower percentage. To answer the “What is a good average” question: your vertical ratio should be under 10% if you want to run with optimal efficiency.

Vertical Oscillation
Vertical oscillation is literally the height of you bounce when you run and it is measured in centimetres. Ideally, you would want to lower your bounce and add those few centimetres to your forward movement. But once again, of all the variables that determine that, your natural running style plays the biggest part.

In essence, the shorter the stride, the lower the bounce, but even that can come under scrutiny. High jumpers run up to the bar with relative short strides, but enormous bounce. What is a good average for an average runner? Lower than 12 centimetres will save you from looking like a gazelle in most cases.

Ground Contact Time
Ground contact time (GCT) is how long your feet stay connected to the ground when you run. The better and faster you run, the shorter your GCT is. If you want to look at it from another perspective, GCT is that split second when you actually do not move, when your leg contracts like a spring to push you into your next stride.

Good runners dip below 200 milliseconds, average runners between 220 and 300. More than 300 means your running style, fitness level, weight and other factors are making running a very laborious exercise for you and guidance might be necessary. In terms of running style, over-striding causes long CGT’s. Weight and unfitness should be addressed on their own terms, otherwise injury is sure to follow.

Ground Contact Time Balance 
Ground contact time balance is the last parameter and it is of great value. It is reflected as a percentage. Since our bodies are not symmetrical, one side works slightly differently from the other. For example, the left and right leg would be reflected as 51,1% and 48,9%. Take note, this does not mean the left leg does 51,1% of the work.

It actually indicates that the left leg is less efficient. Good runners have shorter CGT’s. In this case it means that the right leg is more efficient and pushes off the ground faster. That is why its CGT is shorter. Your weak leg stays longer in contact with the ground. Your objective then should be to improve the strength of the leg with the highest GCT percentage.

This, in short, is what the HRM-Run strap tells you. If you want to scrutinise your running data to become a better athlete, get yourself an HRM-Run strap and use the technology to your advantage. The better you run, the more you will enjoy it. Go for it! – (c) 2017 NavWorld

About The Author

Frank Smuts is a triathlete and writer at www.everfit.co.za.

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