Last time we started a post-series talking about running-watch running dynamics and what part cadence plays as a metric for triathletes. Today we’ll be covering two other metrics that new running-watches are capable of tracking and discuss why you should be paying attention to them.
Ground Contact Time
In all honesty, the remaining metrics are really only derivatives to that of run cadence. However, these are still great data values to track and are very representative of where you are in your running form.
Ground contact time (GCT) is literally the amount of time your foot is in contact with the ground upon each step. This metric is measured in milliseconds. Naturally, as speed increases your ground contact time decreases. As you might have guessed, elite runners and elite triathletes have the lowest GCT.
Interestingly, a novice triathlete is not able to sustain as low of a GCT as that of an elite runner even if they’re running at the same speed. This is because your GCT is determined by your leg stiffness, force production, and, of course, foot position.
Leg stiffness refers to your legs’ ability to transfer energy to the ground. A stiffer, stronger leg will respond quicker to the “free” energy of the ground. Think pogo stick vs. a slinky.
Force production is your power. This is similar to stiffness, but relates more to your pushing off strength rather than your ability to absorb quickly and transition.
Lastly, foot position is what we already covered in the cadence discussion from Part I. When your foot is under your center of gravity, it’s that much easier to continue forward momentum. Remember: 12:00 o’ clock vs. 10:00 o’clock.
As you might have guessed, elite runners and triathletes excel in all of these, which is why their GCT is lower. Increasing your cadence will help to decrease your ground contact time.
Additional extra curricular activities to help with this include post-run strides. Try to do 4-8 sprints accelerating gradually from moderate to top speed over 50-100 meters post-run at least once a week. This is a great, simple exercise, which gradually encourages quicker foot speed and will help improve the GCT metric.
Lastly, the vertical oscillation (VO) metric is the amount of bounce, or vertical up and down movement, your body goes through on each stride cycle. This is measured in centimeters from a fixed point in the stride. Whether we’re looking at an elite runner or a novice triathlete, the majority of runners are going to oscillate somewhere between 6 and 13cm.
So yes we all run differently, but for the most part less bounce is beneficial. The higher you push yourself up through the air means the more energy you’re wasting. We want to go forward. Not up. Also, a higher bounce means more impact when coming back down. The acceleration of gravity isn’t going to change any time soon. Therefore, higher oscillators have an increased likelihood for injuries as their impact with the ground is that much more stressful.
Obviously, all running requires some level of VO. It’s the only way we can go airborne and, thus, move forward. The question is, what is excessive? There are probably too many variables at play to say that something like 8.6cm is the ideal oscillation for you. Similar to cadence, it’s not necessarily important to try to equate yourself with what an elite triathlete is doing. Rather, focus only on making small improvements for yourself.
What I find most beneficial about this running metric is the ability to analyze your VO at the start of a long run versus your VO at the end. This is a wonderful graphical representation of how much your form is deteriorating over the course of the run. Most likely you’ll see your VO increase as the run transpires. This may seem incoherent because you would assume that as you get tired you’d have less energy to jump higher. However, lower VO actually takes more energy and is dependent on proper form.
Therefore, you can use this metric to track just how much your form decays and, on average, how long it takes you to deteriorate that much even if pace is upheld, which is probably much more difficult to uphold at the end of your run than it was at the beginning. Improving your body’s strength, which directly affects its ability to maintain form when cardiovascular fatigue sets in, can always be helped by heavy weightlifting and plyometrics.
Squats and jumping drills are excellent exercises that directly target the muscles responsible for technique fatigue – specifically the glutes, hamstrings, and core. If possible introduce strength work into your triathlon routine and track your VO improvements week after week.
While tracking the metrics of GCT and VO are not a necessity for triathletes or runners, they do offer secondary insights (in the context of run cadence) to your overall running technique and performance.
TALK WITH TRIDOT:
Have you ever paid attention to GCT or VO? How did these metrics inform you in your training?
JARED MILAM is a professional triathlete, TriDot coach, and member of the Tri4Him Pro Team. He has 16 years of competitive running experience and 11 years of competitive triathlon experience with a half Iron PR of 3:59 and a full Iron PR of 8:30. Coaching under the TriDot system since 2011, Jared loves working with aspiring triathletes of all ages and performance levels.