Garmin 500

Dave Barr

Wondering what people have the bike setting for data recording of POwer set to.  The options are Zero avg and non-zero avg.  Mine is currently set to zero avg.

Thanks

Dave

trisumai

always add zeros otherwise your NP (I think) will be messed up.

Steve West

x2 on the always include zeros for power.

John Withrow

x3 on "zero avg". It better captures the real physiological cost of your ride. And forces you to not be lazy in coasting downhills...

William Jenks

The only old excuse for NZAP was that NAZP is reasonably close to NP if you ride relatively steadily. Old Garmins couldn't do NP. It still wasn't a great practice, but some of us did it, including me for a while. However, the 500 will pick up your NP, so there's no excuse at all. :-)

Joe Hallatschek

Taking a chance in posting on this old thread, but I have a question on the Garmin 500 screens.

Right now, if I want to know my lap IF, I have to manually divide my lap NP by my FTP when I download and analyze my workout. All I can find for screen options on my garmin is just IF, which measures my entire workout. Is there some option for lap IF under some other name?

Gaudir8

Joe I have an 810 and there is no option for IF by lap. Crazy isn't it. The only thing you can do is use Lap NP or Lap power and know your range. But you still would have to calculate the lap ftp

Paul Hough

Hmm, now I am going to have to check my 500 to see if I am averaging zeros or not!

Joe Hallatschek

@Ray - thanks.

Averaging zeros - although it might make sense outdoors, I don't see it making a difference on a trainer. I certainly don't coast to a red light or go downhill and so I don't think it matters, right? Am I missing something?

Gaudir8

I agree Joe I guess the only thing would be if you forgot to change it back when you hit the  road.

Joe Hallatschek

Issue - I have uploaded my garmin data and I am looking at my splits. My average power is higher than my normalized power. In RnP's power webinar, I thought the VI was NP/AVP and the discusion was that a goal was a VI of 1.0 or 100%. Also that a VI or 1.02 was a flat course and 1.17 was hilly.

So, my VIs range less than .967 to 1.0 for my intervals and only go over 1.0 for my warm-up and rest between intervals.

Bottom Line Question: do I have my math mixed up? If not, what does my VI mean, am I doing something not quite right?

Thanks!

Gaudir8

Joe I had the same thing on my splits. What is happening for me is I am getting on it early spiking my power and then loosing it at the end. While my average power is higher the NP is spreading that out over the distance where my initial spike of getting on it is much more smoothed out. The other issue is the short 2 minute duration of the repeat.I hope this makes sense? Below is from Training Peaks

Andrew R. Coggan, Ph.D.

One of the first things that catches the attention of any beginning power meter user is how variable, or "jumpy", their power output tends to be. This is largely due to the constantly changing resistances (e.g., small changes in elevation, gusts of wind) that must be overcome when cycling outdoors. Because of this variability, training with a power meter is not directly comparable to training using a heart rate monitor. In particular, it is very difficult (as well as counterproductive) to try to keep power constantly within a certain range, or zone, at all times during a training session. Just as importantly, this variability means that the overall average power for a ride or part of a ride is often a poor indicator of the actual intensity of the effort. This is especially true for races, since power can vary dramatically from one moment to the next as, e.g., a rider first tries to conserve energy and then attacks.

To account for this variability, TrainingPeaks uses a special algorithm to calculate an adjusted or normalized power for each ride or segment of a ride (longer than 30 seconds) that you analyze. This algorithm is somewhat complicated, but importantly it incorporates two key pieces of information: 1) the physiological responses to rapid changes in exercise intensity are not instantaneous, but follow a predictable time course, and 2) many critical physiological responses (e.g., glycogen utilization, lactate production, stress hormone levels) are curvilinearly, rather than linearly, related to exercise intensity, By taking these factors into account, normalized power provides a better measure of the true physiological demands of a given training session - in essence, it is an estimate of the power that you could have maintained for the same physiological "cost" if your power output had been perfectly constant (e.g., as on a stationary cycle ergometer), rather than variable. Keeping track of normalized power is therefore a more accurate way of quantifying the actual intensity of training sessions, or even races. For example, it is common for average power to be lower during criteriums than during equally-difficult road races, simply because of the time spent soft-pedaling or coasting through sharp turns during a criterium. Assuming that they are about the same duration, however, the normalized power for both types of events will generally be very similar, reflecting their equivalent intensity. In fact, normalized power during a hard ~1 hour long criterium or road race will often be similar to what a rider can average when pedaling continuously during flat 40k time trial - the normalized power from mass start races can therefore often be used to provide an initial estimate of a rider's threshold power (see below).

Although normalized power is a better measure of training intensity than average power, it does not take into account differences in fitness within or between individuals. TrainingPeaks therefore also calculates an intensity factor (IF) for every workout or time range analyzed. IF is simply the ratio of the normalized power as described above to your threshold power (entered under "Athlete Settings" at your "Athlete Home"). For example, if your normalized power for a long training ride done early in the year is 210 W and your threshold power at the time is 280 W, then the IF for that workout would be 0.75. However, if you did that same exact ride later in the year after your threshold power had risen to 300 W, then the IF would be lower, i.e., 0.70. IF therefore provides a valid and convenient way of comparing the relative intensity of a training session or race either within or between riders, taking into account changes or differences in threshold power. Typical IF values for various training sessions or races are as follows:

Joe Hallatschek

@Ray - this is a keeper. So, my IF calculations are correct. I am doing exatly what you described in the 2' intervals: building up, spiking, and then bringing down to my target.

Rich Strauss in the power webinar gives this example: "if you ride 30' at 125 watts and then 30' at 275 watts, your av power is 200watts. But your NP is 234 because it is the real cost in watts of the ride". So, not understanding the math, what I get out of that is NP should be higher than av power. The goal of course is to get it to 1.0.

So, I guess I will continue to use NP and just "believe" and drink the koolaid. But if I can break the code, I'd be able to figure out how to take Rich's concept and apply it. It would seem that the only way to do it would be to be at my target watts at the start of the interval and keep it steady for 2'. Then, the interval would really start before the 2'.

I think the big idea is to just get to the target as quick as possible and hold it. So, with that, I'm good. Thanks for the good discussion!

John Withrow

Joe, keep drinking the power Koolaid, but don't get too caught up in the minutia. What you discovered with NP greater than NP is something I struggled with in some of my FTP tests last yr. If I can dig up the thread, I'll post it here later. I think the answer is actually a technical one regarding how the calculations are actually done. In almost all 'real world' cases, NP 'must' be the same or higher than AP because the math requires this. However for short intervals of big efforts proceeded by a low rest level, the math gets screwy. I've even seen it for a 20 min interval if it's very high and steady and proceeded by a lower power level. This is especially seen on VO2 sets because the big discrepancy between ON and OFF power levels. To simplify what happens with the math (I think...), AP simply uses the data set that starts when the interval starts and ends when it ends. However, NP is much more complicated and actually uses a rolling average to calculate it over a certain period of time (like 15 or 30 seconds or so). So for the first 15 or 30 seconds of your interval, it actually uses some of the data points before the interval actually starts. Since these earlier data points are from your rest interval, the NP can actually calculate a lower number. This is the same reason when you start your initial ride at t=0:00 and show AP and NP as readouts on your device, the AP will show immediately, but the NP will be blank for many seconds until there is actually enough data to calculate NP. So for me, for FTP tests or VO2 intervals, I assume the higher number (AP or NP) is the right one and I don't get to worried about IF for these.

Peter Greagg

JW you are indeed a WSM.
Most head units that give NP use a rolling 30 second average to calculate it — meaning that if you were on, say zero watts for 30 secs before starting the interval, even if you sat on exactly, say 200 watts, then your AP would be steady at 200 watts for the whole interval, whereas the NP would continue to rise over the whole interval — and in the example I gave, NP would always be lower than AP.
Another manifestation of the 30 sec rolling average is if you stop during a ride, your AP wouldn't change while you are stopped whereas your NP will fall for 30 secs — also, when you start again, it takes 30 secs for the rolling average 'buffer' to refill, so NP 'appears' artificially low during that period.

Joe Hallatschek

@John and Peter - the "rolling average" for NP vs. the discrete interval measurement for ave power provides me the exact math I needed. So, for these short intervals, the right answer is the higher number.

I actually backed into that answer today when I tried to get to my target watts as soon as possible for the 10' and 15' intervals. My NP and AP were almost exact since the interval was longer and the 15'/30' before my interval started was higher.

Thanks guys for the explanation! More koolaid please!