Friday, March 07, 2008

Bicyclist's Best Buddy

A spare inner tube?

Perhaps a pump?

Food and drink?

A chain tool?

All of those in it's time or place, but my really best bicycling buddy is a Heart Rate (HR) Monitor.

One of the things I did the first spring after I dusted off the bike again was to buy a HR Monitor: just a basic creature which showed me my current heart rate and kept track of the amount of time spent above, in or below a target zone which I could program into it; the time data could be retrieved at the end of a ride (just 3 numbers, nothing fancy). It didn't keep track of the maximum rate I drove the poor thing up to though, which turned out to be something I think now I should have had; it would at the time have required going one model up-market, for about another $30.

Initially I bought it because I was arriving home from rides in a pretty stressed state, physically. (I live on top of what was then a very significant hill which I used to charge up, about 50m high as near as I could tell from a map, although later when I had an altimeter I found out it was only 30m high; and prior to returning to the bike I had a fairly sedentary lifestyle, at least as far as aerobic activity was concerned). (the hill is still as significant, it just doesn't kill me to ride up it anymore: I have learned how to defeat it). With the HR monitor I found out that when I came up that thing I was exceeding the theoretical maximum HR for my age by about 15%! So I stopped attacking the hill so hard and probably the HR monitor saved my life; I guess that was worth the hundred bucks (some might argue that, but you'll have to feed me wine to get me into that conversation).

Well, maybe it was just me, and the rest of you are more sedate in your approach to the last hill of the day: but my brain was stuck at 18, while my body certainly wasn't. Nor could I now push the gears uphill that my old racing bike of the early '70's came with-- that was before the days of mountain biking and mountain bike gears. I should also admit that I got the HR monitor because it was a current tool of the racer training, and if they had been available in my teen years I would have wanted one; I just have to have all the gadgets I can manage -- this will be a recurring theme here... So with the HR monitor, initially a bit of any eye opener.
I still consider the HR monitor, whether a basic or a more complex model, to be the cyclist's most important tool, maybe even ahead of a pump, wrench, screwdriver, and odometer.

Two years ago I decided that I wanted to know about hill heights and wanted to look at HR data after a ride, so I got a HR unit with a heap of features (overkill, really, if one is allowed to use that expression in a discussion of heart rates!!): an onboard memory which could be downloaded to my PC after a ride. (also a power meter add-on of some sort). It's a gadget, so of course... Anyways... It did provide me with the graphic data that I use in these articles.

Youngsters will probably laugh themselves silly at the low power and HR numbers seen on the graphs, but hey, it's the best I can do just now.

With the more sophistocated HR monitor came some literature and website info that got into the whole "HR as a training tool" issue, and from that I did some more reading and researching. Now, most of what I came across is not particularily relevant to the average Recreational Cyclist, but some of it turns out to be very much relevant, in my opinion. That's what I'm going to discuss here.

First a bit of physiology, as I understand it, and condensed by me.

Aerobic vs Anaerobic effort: Aerobic effort is when the physical activity is taking place at a rate which allows sufficient oxygen to get to the muscles for them to "burn fuel" cleanly, that is without producing toxic waste products. Aerobic cycling is a Good thing. Anaerobic effort is when the blood stream cannot supply sufficient oxygen to the muscles for clean burning, and so a different chemical process results and toxic byproducts such as the dreaded lactic acid build up in the muscles. And this is a Bad thing. Logically, one would expect the body to scream foul when one drives it hard enough to go anaerobic, but it doesn't really scream loudly enough until one has either been mildly anaerobic for an extended period or is quite heavily anaerobic for a short period. In terms of Heart Rate, the changeover between aerobic and anaerobic occurs somewhere around 90% of a person's maximum HR. A person putting out an effort slightly above the Anaerobic Threshold can only maintain it for 30-45minutes, after which pain and fatigue force reduction to aerobic levels of effort. (Trained athletes can work at their maximum HR for only 2 minutes or less.)

(The literature sort-of treats the Aerobic/ Anaerobic threshold like a switch, ie either one or the other, but that doesn't quite compute to me and I personally think of it as both processes going on together during a changeover zone. In practice this might mean that some muscles are being overworked and under-oxygenated earlier than others, for whatever reason)

Once a body has worked anaerobically and then returns to aerobic rate of effort, the byproducts of the anaerobic period are cleaned up by the body; how long that takes depends on the concentration of byproducts in the blood and muscles, and the level of effort that the body has dropped to. That is: if you keep cycling along at a HR just under the point where you become anaerobic there is little slack in the body engine for cleanup, whereas if you are proceeding at a much more sedate "Recovery Rate", cleanup is more rapid. In a fairly fit individual, one minute of maximum effort (ie close to his/her maximum HR) requires at least 10 minutes at a Recovery rate for complete recovery.

Recovery HR is at or below about 55% of the HR at which anaerobic activity starts (called the Anaerobic Threshold, or Lactate Threshold). More usefully, it's at about 60% of maximum HR. In terms of power output, it is much less than half of the power output at the Anaerobic Threshold. So one really does need to go sedately when recovering from a big hill.

While I'm on that, physically the worst place to stop cycling is at the top of a hill. Easy pedalling for several minutes after an exertion helps blood circulation in the leg muscles, whereas stopping abruptly somewhat reduces the blood to the muscles and thus the recovery. Unfortunately, the best views tend to be from hilltops. So for the recreational rider, a tradeoff can be to ease off on the pedalling shortly before cresting a hill (racers would cringe at the thought of this, they tend to try the opposite if they can). Or better still go up the hill at an aerobic pace if possible; this means slower pedalling in a lower gear. It is interesting to note that a 5% slope can be climbed at a walking pace with only 40watts of power output in windless conditions, and that's still fast enough to control the bike and not fall over; the same climb at 10kph takes about 100watts. 40watts is probably in or below the Recovery HR range for most of us in the CCC and not much above it for the rest. Flat terrain at 20kph takes about 60watts on a windless day (at 25kph, about 120w; at 40kph about 400w). That's not just a string of numbers, but rather hints for riding strategies.

Another little aside:
Recovery: There are about 4 main stages of recovery, as I see it. First is what we might call HR recovery, which happens when you back off from an effort and after awhile your HR starts to drop until it reaches the rate appropriate for your activity level. If you are at a work rate higher than that at which you can go to the next stage of recovery, any little increase in effort will result in an immediate increase in HR-- you are basically riding a tight-rope there and your blood components are in a steady-state. That next level of recovery is sort of a System recovery (my term for it, you probably won't read this elsewhere in the same words)during which you are working at a rate at which your body can burn off the toxic effects of anaerobic activity; the lower your work rate, the faster the cleanup. Third is Resting recovery, essentially an overnight activity, during which repair to muscle fibre etc which has been strained during the ride is possible. Fourth is sort of Enforced Rest which is necessary if you really overstrain your cardio-vascular system, a state which used to be called burnout (which was treated by coaches yelling at you louder and giving you extra work as punishment for "bad attitude") but which is now known as Overtraining Syndrome (treated by, you guessed it, enforced rest)

Is there more to this anaerobic activity than just tiring the muscles faster and requiring a longer recovery? Well, yes: in the worst case your muscles will actually weaken from the exercise rather than strengthening. The by-products of anaerobic activity are toxic, and at high work rates the body engine can choose to use muscle protein for fuel in preference over more usual forms of fuel like carbohydrate derivatives and (at relatively low levels of effort) fat. So unless there is a trophy or a goodly prize purse at the end of the ride, why would you want to do this to your body, knowing what you do now?

The converse of this is that muscles are better strengthened when worked at aerobic rates so there is a double bonus to keeping the heart rate down. The trick to strengthening the leg muscles on the bike is to work them as hard as possible without becoming anaerobic. This is tricky to do without a HR monitor; I find that I either go too hard or else feel like I am working at just the right pace when in fact I am quite a bit more relaxed than necessary or optimal.

Within the aerobic range you will (hopefully) find a work rate which you can maintain for quite awhile without getting weaker: a slight increase over that, while still aerobic, will result in slowly losing power over time without the heart rate falling off.
Does it matter to the recreational cyclist if their legs get stronger over time, or if their strength gradually reduces during a long ride? Well, apart from the obvious get-there-faster or -earlier thing which may not matter on any given day, it turns out that the more sustainable power you can put into your legs the less weight there is on your bike saddle! Yes, it's true; your feet support part of your body weight when you pedal, and the more force on the pedals the less on the sit bones. That can matter a lot...

Riding at a sedate pace does have an interesting side-effect hinted several paragraphs ago: it turns out that the fuel of choice of the aerobic engine at the lower range of aerobic activity (65-80% of one's maximum HR) is fat, not carbohydrates. Some fat will still be burned at higher heart rates, but it is a secondary fuel then.

A couple of other miscellaneous points on this subject... research has found that at the start of exercising it takes about 10 or more minutes to kick-start the aerobic engine and get it burning efficiently. During that first short period the body operates essentially in anaerobic mode. Ah-ha! the mythical "second wind" is no myth at all, it is a real physiological event.

This probably goes a long way towards explaining why those first few kilometers after our extended lunch breaks always feel like death is imminent (well, it does to me!). For me, improvement in power output vs heart rate continues for about a half hour or so before my engine is really ticking over optimally. The graph shows me at the start of a ride session; notice how after an initial peak HR drops off while power continues to increase.

Second, by alternating short periods of anaerobic affort with longer periods of aerobic effort just below the anaerobic threshold, the body can be trained to become more efficient at flushing anaerobic byproducts. Important to racers, but this is type of training is hard on the body and for the recreational cyclist it is probably better to try to avoid that anaerobic bit, or if unavoidable take a nice long slow recovery period afterwards. Finally for what it's worth, like all body functions, a person's Anaerobic Threshold drifts a bit from day to day and even from hour to hour, depending on how rested the body is.

Also of note, the consensus seems to be that no amount or type of training can change an individual's maximum HR or HR at Anaerobic Threshold significantly (at least not in a positive direction!). That is, at least as concerns the adult body; I haven't come across anything on whether or not they can be affected in childhood. The objective of the cyclist seeking to improve, whether professional or casual, is to increase power output at any given HR, i.e. stronger legs for more fun. On which, for those who say that as recreational cyclists they do not train, I'm of the opinion that every time you ride a bike you are training for your next bike ride just by making the pedals go...

Is there a way to tell when you are crossing into anaerobic effort, from the "feel" of your body? Unfortunately, at least in my own case, not until things are fairly well along: that is, significant lactic acid buildup has already occured. Possible tell-tale signs:
- heavy breathing? Not really, my breathing seems equally laboured (or unlaboured) once I reach a rhythm, whether 20 beats per minute (bpm) below my Anaerobic Threshold or 10 bpm above it. However, when I am gasping for air uncontrollably then I know that I am near or at my maximum HR and need to ease off considerably to recover from the effort, but by then the damage to my endurance is done.
- "burning" feeling in the leg muscles? Definitely, yes: the burning sensation is caused at least in part by lactic acid buildup, but again one doesn't really feel it until there is more than a bit of it. It's possible too to get a minor burn for a short period after starting an increased effort even if the effort is not anaerobic once you settle into it.
- legs feeling "heavy" or engorged? Yes, could be an indication of a lower level of lactic build-up before getting to the burn stage. But could also be an indication that you need to take in some fuel or even water.
- if the slope of the road hasn't changed or the wind increased and you have felt like you have been riding at the same effort but your speed is decreasing "significantly", that could indicate increasing lactic acid levels, or might mean you need fuel or water. But this is Nova Scotia where the road never holds a consistant slope and the wind is always shifting direction and speed, so I think that's a non-starter as an indicator!
- a Heart Rate monitor does give a very good and reliable indicator of when you are working at an anaerobic rate. I'll explain how to make use of one a bit further on.

By accident I have bumped into a description of some readily discernable physiological effects generally experienced at some of the effort rates:
- a thing called the "gossip threshold": at a "minimal" activity rate, up to 80% of maximum HR, it's possible to carry on a chat without getting out of breath. But approaching this 80% probably can't sing Mozart opera; maybe a bit of Gilbert & Sullivan "patter" song, soto voce.
- at a "light" activity rate, 80-90%, conversation isn't possible but control of breathing technique is possible despite having to breathe deeply. At the upper end of this range, one is flirting with anaerobic effects. Fit folks should be able to maintain this activity rate for over 30 minutes.
- above 90% is the anaerobic zone; one cannot control one's breathing; rather, the need to breath controls the rider. (on a personal note, though, I find I can yell at charging dogs [or rude/ inattentive motorists] regardless of my HR zone-- but I guess that's an adrenalin thing!)

Some, if not most!, people are probably more in tune with their body responses than I am, and may be able to tell the onset of anaerobic effort more readily than I can. But I think they can only do that if they have a milestone to learn from. Which means riding with a HR monitor for awhile and paying attention to it.
Of course some of you have been riding long enough that you can perhaps set a pace which you can maintain all day without problem. I used to "know" that I could, until I ran into more information and started paying attention to it this fall. Yes, I could spend the whole day riding and still get up the hill to home (not just the final 30m rise but the whole 200m above Windsor), but with hindsight I know now that going through the Rawdon Hills early in the day put me into oxygen debt which I never really got out of, and every subsequent hill reversed some of the recovery that I had somehow managed.

Using the HR Monitor

So how might a recreational cyclist make use of a HR monitor?

First off, you really don't need to know exactly what your Anaerobic Threshold is; racers like to so they can maximize their power output for the race, whether that means going above it for a few periods or not; but recreational riders should probably avoid getting that close to the edge.

So, when you buy a basic HR monitor it should come with a booklet including charts of reasonable exercise zones for varying levels of fitness and age and sex. These will have been approved by the manufacturer's legal department, so tend to be on the conservative side. But for non-competitive activity conservative is great. (The booklet that came with my first, basic, HR monitor recommended 50-70% of HR max for Beginner users, and 70-80% for Advanced users (also 80-100% for Competitive users)).

Start off by calculating your theoretical maximum HR. A popular formula for this is a medical standard, so the industry uses it with impunity. It is nicely straightforward, 220 minus your age in years. There are some slightly different formulas out there though; the one that came with my first HR monitor (Sigma Sport) is 210 minus half of age with a small adjustment for weight (minus 0.11 x weight) and a slight fudge factor for men (it seems the ladies have better hearts but we mostly knew that already anyways, right guys?). For me, the latter formula gives a higher number over the simpler formula, by about 6 at this point in my life.

Next, there are a couple of numbers to determine, based on a percentage of your theoretical maximum HR.
- exercise Target Zone. This will be easily aerobic, and for average non-competitive folk will be about 65-80%, or the 50-70% mentioned earlier if you prefer. Well, cycling at a HR lower than the bottom of the range is still useful aerobics too. I think there is a bottom end to the target zone so that folks sweating in a gym will feel they are getting their money's worth out of it. So let's just say under 80%.

- approximate Anaerobic Threshold: use 85% of maximum initially (90% if you are fairly fit-- not to imply that your threshold will be higher if you are fit, just that you will be better able to deal with the stress of going to or over it); if this turns out to be too high or too low you can adjust it downward. This is a HR to avoid reaching whenever possible. But keep in mind that your HR response will lag your physical effort by 30 seconds to a minute so you really need to start easing up on your pedals and/or gear down some time before that number pops up on your HR monitor! Experience will teach you how much time depending on how hard you're working. From the perspective of endurance, better to slow down early and sneak up on the maximum rate you've set yourself rather than going past it by accident and having to drop back and recover from it.

- your Recovery zone, to follow up those occasions when you can't avoid going a bit anaerobic. Use 60% of maximum as the upper limit. Or even less if you want (not too much less or you'll need to have a hammock with you).

This graph shows how the effort required to maintain a work rate increases dramatically as HR increases. Remember the old "10 percent rule" in which 90 percent of the effort goes into the last 10 percent of quality of the final output? Well, there it is again. Of passing interest, at zero heartrate one just ain't making an effort...
For the curious including George, the numbers 1-5 on the curve itself refer to the lower limits of an example of HR Zones for use in training or riding: Zone 1: Maximum intensity, Zone 2: Hard intensity, Zone 3: Moderate intensity, Zone 4: Light intensity, Zone 5: Very light intensity. Different coaching/training philosophies use different Zone heirarchies but the effort v percent of HR curve remains the same.

The bottom line in all this is that a large exertion to get up a hill a few minutes faster could very likely end up costing you more time (and energy) over the duration of a long ride than what you gain on that hill. The first few minutes of over-exertion will produce an increased power and speed, but before too long your power output will be at best only slightly greater than if you had kept a more reasonable speed, but your heart will still be pounding away like heck and your exertion level will be still be high. Here are two charts showing this effect.
These compare my outputs on two rides over the same simulated terrain on the I-magic trainer (the pale green shading shows the terrain; looks pretty severe but the maximum elevation equivalent is not really all that high, only about 50m if I recall correctly). The first graph shows the entire route, the second one zooms in on a small segment. The rides were about 3 months apart so aren't really directly comparable but the trends are shown clearly enough. The solid lines are from the most recent ride, in which I tried to keep my HR around 135 at all times (for reference, at 130 I am able to recover slowly or maintain a steady power output for over an hour, at 137 I have poor recovery and lose power during an hour). The dotted lines are data of the first run, during which I tried for HR 130 on the flats and 155 on the "climbs". Note how power output (the green line) is about the same on all the flats in the solid run, but is lower and lower in the flats after each hill set in the dotted run. Note the extra effort of the dotted run results in a shorter overall time by only 1 minute over a total time just under 70 minutes. In fact, both riders start the first hill set at the same time, the dotted rider comes back on the flats a few hundred metres ahead of the solid one, but by the foot of the second set of hills has almost been completely caught except for about 20m (you can't see this on the graph, but you can see the differences in the blue lines, speed, between the two).

(For inquiring minds: Bike racers are subject to the same problem, except that being more fit and properly trained (in theory) they recover faster, and it is worth their while to turn themselves inside-out to keep up with the rest of the race because at their speeds (even up mountains) there is a great advantage to riding in someone else's slipstream. Plus they don't get to stop for lunch at interesting places.)

There's nothing wrong with recreational cyclists pushing their body into anaerobic efforts if you know that you're doing it, limit the duration, recover reasonably, and have some kind of a plan or objective. But I'd suggest that for most the best time to do it is not the first hill of the day but rather towards the end of a group ride or shortly before the lunch stop (the sprint for the table with a view). Remembering of course to take time and distance to cool down gradually before actually stopping.

Now, if you still don't think a HR monitor can help you ride more enjoyably and with less strain, I didn't do a very good job of explaining myself... (no news there, some might say). Finally, I will now come clean and tell you that I do not work for, or in any way benefit from sales of, any brand of HR monitor!

Labels: , ,


Post a Comment

Links to this post:

Create a Link

<< Home