Quantifying training

Why Use a Model? Training models try to capture quantitatively several training principles what we all know from experience: Any training I do today will make me swim faster in the long run (perhaps a few weeks or months from now) but will actually make me swim slower tomorrow. That's why we pile on the training in the months before a focus event, and taper for a few weeks ahead of time. Working hard is more valuable than being lazy. So if we already know this, what's the point of using a mathematical model to tell us the same thing? Mainly so that we can optimize our training. When, exactly, should I start my build phase: 5 weeks out? 8 weeks out? How long should it last? Am I better off swimming 1500 yards of intervals today, or 3000 yards of straight swimming? How long should I taper? Et cetera. Having a mathematical model allows us to answer questions about which of two training approaches might result in more optimal preparation. Plus, it's a great excuse for some of us to get our geek on. Impulse-Response Models The basic concept behind all of these models is that you keep track of fitness and fatigue separately. Every workout will increase both fitness and fatigue. At first, fatigue increases by much more than fitness in response to any training. For example, suppose I swim a workout today that increases my fitness by 100 "points" (more on this below). That same workout will increase my fatigue by 200 points. Because of this larger increase in fatigue, I would swim slower in a race tomorrow than if I hadn't trained today. But the effects of training (the "response" to this training "impulse") don't last forever. Both fitness and fatigue decay over time as we become untrained. Luckily, fatigue decays a lot faster than fitness does. Roughly speaking, you can think of fatigue as having a half-life of 10 days or so, while fitness lasts longer, with a half-life of about 30 days. The next thing to recognize is that all of this is cumulative. My fitness, today, consists of that 100 points from the workout I did this morning, plus half of the the points from the workout I did 30 days ago (because its effect has decayed), plus some smaller fraction of what I did 3 months ago, etc. Fitness is the sum of all of these past "training impulses", each of which began to fade as soon as it was finished. Likewise for fatigue, which starts larger but fades faster. The last piece of the puzzle is to define a performance score as the difference between fitness and fatigue. Think of fatigue as merely masking the fitness you have built up. It's in there, you just can't tap it because of the accumulated fatigue. That's why a 1-2 week taper is typical -- it lets the fatigue fade away without waiting so long that fitness decays too much. This difference between fitness and fatigue is what you try to optimize on race day. The math involved is actually relatively simple (although I'll save the details for another post). You don't actually have to keep track of every workout you have ever done. You just track a cumulative fitness and fatigue score. Just like counting yards, but you're counting "points" instead. Then every day those scores fade a little bit, and you may add onto them if you do some training that day. Quantifying Intensity So how do you determine how many "points" a workout is worth? That's where things become trickier. There are a lot of different approaches. The key is that these point systems need to recognize that swimming hard is worth more than swimming slowly. Heart Rate The first of these impulse-response models was Banister's TRIMP (training impulse) model. In that model, your heart rate is used to calculate points, where points rise exponentially with heart rate. For example, I can earn 6 points per minute if I'm exercising at close to my max HR, but I only earn 1 point per minute if I'm floating along at 120 beats per minute. The big advantage of using heart rate to calculate points is that it can be used across many sports. A TRIMP earned in the pool is the same as a TRIMP earned running, or cycling. This makes it particularly valuable for multisport athletes, like triathletes, or for those who want to include cross-training in their training. It's also a physiologically meaningful indicator of training intensity, and there is lots of data correlating heart rate to other physiological variables like lactate levels, etc. There are two big disadvantages for swimmers, however. First, it's tricky to track heart rate while swimming. Heart-rate monitors are difficult to wear in the pool (for men, anyway) and are too much hassle for most swimmers in any case. Counting your pulse after a set is inaccurate at best, and only tells you your heart rate after you've stopped swimming. Secondly, heart rate rises fairly slowly in response to exercise. That's no problem for a 1-hour run, but can be a real problem for a 30-second swim. Zones Because of the various practical problems with using heart rate, a simpler approach is to use a collection of intensity zones. There can be as many or as few zones as you like. For example, one approach awards 1 point per minute for easy pace efforts, 2 points per minute for sub-threshold efforts, and 3 points per minute for efforts above threshold. Alternatively you can use an RPE scale (rate of perceived exertion) from 1-10 or 1-20 and assign different point values for each level. These zone-based point systems have the disadvantage of being subjective. They are also inconvenient because the calculation can't be automated via a heart rate monitor or power meter. For swimmers, it may be inconvenient to assign effort levels and durations to different parts of a workout that consisted of many sets & reps on different intervals. Rick Sharp's Stress Score One example of a zone-based method is Rick Sharp's training stress score. With this approach, each minute of training gets 0 points if it was part of warmup or recovery 2 points if it was part of an aerobic endurance set (long distance pace, short rest) 6 points if it was part of an anaerobic power set (80-90% max HR, 100-500 yard reps, moderate rest) 8 points if it was part of a lactate threshold set (50-200 yard reps, hard effort, lots of rest) 4 points if it was part of a sprint set ('t require HR or other data collection, but can still be somewhat subjective if your set doesn't fit cleanly into one of the predefined categories. This stress score is built into the Hy-Tek's Personal Swim Manager software. It also has the advantage of being transferable relatively easily to other sports, since it is based only on duration and effort levels that translate well into other sports Power The most common method of assigning points to different exercise intensities is to use power measurements. For cycling, in particular, power meters have become common training tools that can log the power output at frequent intervals duirng a workout. These power logs can then be used to calculate a point score for a workout. As with heart rtae, points are a very nonlinear function of power in an attempt to reward higher intensity appropriately. In Coggan's very popular TSS (training stress score) point system, 100 points corresponds to a 1-hour time trial done at 100% effort, although you can earn those same 100 points by doing intervals at higher power or longer rides at sub-threshold power. Power-based point systems have a number of advantages. As a measure of intensity, power is completely non-subjective, and can be correlated with physiological variables such as lactate ion concentration. The availability of power meters for bicycles means that data collection is automated and fairly simple. There are a number of different software programs and websites that can perform not only the point calculations, but also the impulse-response modeling of the training plan, and even the construction of a training plan. In principle, power is fairly transferable to different sports. Generating 200 W while swimming would earn you the same number of points as generating 200 W while cycling. Unfortunately, it is difficult to measure power output directly while swimming, and there are no commercial devices that swimmers can use to collect power data. Speed There is no equivalent of a power meter for swimming (or running), but it is easy to measure swimming speeds or swimming times. Because there is a known relationship between velocity and power, times can be used to estimate power, which can then be converted to points of some sort. Skiba's SwimScore is one such method, that performs a weighted average power over a workout using swimming velocities. It is a complex calculation (with several ad hoc assumptions), but there is software commercially available to perform the calculations. In this system, 100 points corresponds to a 3000 m time trial swum at 100% effort. There is a marginal attempt to keep these points comparable to those from Coggan's system (although this is flawed for anyone who swims 3000 m considerably faster or slower than 1 h.) On this forum, qbrain has posted another point system that uses velocity as a proxy for power. The intensity used to calculate his "energy points" is merely velocity cubed, which is propotional to power. This calculation is fairly simple: each rep earns a certain number of points based on the interval time, with no weighted averages required. For example, you'd earn 100 points for every swimming 100 SCY in 1:27, while swimming 100 SCY in 1:02 would earn you 200 points. These points are not easily transferable other sports, however.

Why Use a Model? Training models try to capture quantitatively several training principles what we all know from experience: Any training I do today will make me swim faster in the long run (perhaps a few weeks or months from now) but will actually make me swim slower tomorrow. That's why we pile on the training in the months before a focus event, and taper for a few weeks ahead of time. Working hard is more valuable than being lazy. So if we already know this, what's the point of using a mathematical model to tell us the same thing? Mainly so that we can optimize our training. When, exactly, should I start my build phase: 5 weeks out? 8 weeks out? How long should it last? Am I better off swimming 1500 yards of intervals today, or 3000 yards of straight swimming? How long should I taper? Et cetera. Having a mathematical model allows us to answer questions about which of two training approaches might result in more optimal preparation. Plus, it's a great excuse for some of us to get our geek on. Impulse-Response Models The basic concept behind all of these models is that you keep track of fitness and fatigue separately. Every workout will increase both fitness and fatigue. At first, fatigue increases by much more than fitness in response to any training. For example, suppose I swim a workout today that increases my fitness by 100 "points" (more on this below). That same workout will increase my fatigue by 200 points. Because of this larger increase in fatigue, I would swim slower in a race tomorrow than if I hadn't trained today. But the effects of training (the "response" to this training "impulse") don't last forever. Both fitness and fatigue decay over time as we become untrained. Luckily, fatigue decays a lot faster than fitness does. Roughly speaking, you can think of fatigue as having a half-life of 10 days or so, while fitness lasts longer, with a half-life of about 30 days. The next thing to recognize is that all of this is cumulative. My fitness, today, consists of that 100 points from the workout I did this morning, plus half of the the points from the workout I did 30 days ago (because its effect has decayed), plus some smaller fraction of what I did 3 months ago, etc. Fitness is the sum of all of these past "training impulses", each of which began to fade as soon as it was finished. Likewise for fatigue, which starts larger but fades faster. The last piece of the puzzle is to define a performance score as the difference between fitness and fatigue. Think of fatigue as merely masking the fitness you have built up. It's in there, you just can't tap it because of the accumulated fatigue. That's why a 1-2 week taper is typical -- it lets the fatigue fade away without waiting so long that fitness decays too much. This difference between fitness and fatigue is what you try to optimize on race day. The math involved is actually relatively simple (although I'll save the details for another post). You don't actually have to keep track of every workout you have ever done. You just track a cumulative fitness and fatigue score. Just like counting yards, but you're counting "points" instead. Then every day those scores fade a little bit, and you may add onto them if you do some training that day. Quantifying Intensity So how do you determine how many "points" a workout is worth? That's where things become trickier. There are a lot of different approaches. The key is that these point systems need to recognize that swimming hard is worth more than swimming slowly. Heart Rate The first of these impulse-response models was Banister's TRIMP (training impulse) model. In that model, your heart rate is used to calculate points, where points rise exponentially with heart rate. For example, I can earn 6 points per minute if I'm exercising at close to my max HR, but I only earn 1 point per minute if I'm floating along at 120 beats per minute. The big advantage of using heart rate to calculate points is that it can be used across many sports. A TRIMP earned in the pool is the same as a TRIMP earned running, or cycling. This makes it particularly valuable for multisport athletes, like triathletes, or for those who want to include cross-training in their training. It's also a physiologically meaningful indicator of training intensity, and there is lots of data correlating heart rate to other physiological variables like lactate levels, etc. There are two big disadvantages for swimmers, however. First, it's tricky to track heart rate while swimming. Heart-rate monitors are difficult to wear in the pool (for men, anyway) and are too much hassle for most swimmers in any case. Counting your pulse after a set is inaccurate at best, and only tells you your heart rate after you've stopped swimming. Secondly, heart rate rises fairly slowly in response to exercise. That's no problem for a 1-hour run, but can be a real problem for a 30-second swim. Zones Because of the various practical problems with using heart rate, a simpler approach is to use a collection of intensity zones. There can be as many or as few zones as you like. For example, one approach awards 1 point per minute for easy pace efforts, 2 points per minute for sub-threshold efforts, and 3 points per minute for efforts above threshold. Alternatively you can use an RPE scale (rate of perceived exertion) from 1-10 or 1-20 and assign different point values for each level. These zone-based point systems have the disadvantage of being subjective. They are also inconvenient because the calculation can't be automated via a heart rate monitor or power meter. For swimmers, it may be inconvenient to assign effort levels and durations to different parts of a workout that consisted of many sets & reps on different intervals. Rick Sharp's Stress Score One example of a zone-based method is Rick Sharp's training stress score. With this approach, each minute of training gets 0 points if it was part of warmup or recovery 2 points if it was part of an aerobic endurance set (long distance pace, short rest) 6 points if it was part of an anaerobic power set (80-90% max HR, 100-500 yard reps, moderate rest) 8 points if it was part of a lactate threshold set (50-200 yard reps, hard effort, lots of rest) 4 points if it was part of a sprint set ('t require HR or other data collection, but can still be somewhat subjective if your set doesn't fit cleanly into one of the predefined categories. This stress score is built into the Hy-Tek's Personal Swim Manager software. It also has the advantage of being transferable relatively easily to other sports, since it is based only on duration and effort levels that translate well into other sports Power The most common method of assigning points to different exercise intensities is to use power measurements. For cycling, in particular, power meters have become common training tools that can log the power output at frequent intervals duirng a workout. These power logs can then be used to calculate a point score for a workout. As with heart rtae, points are a very nonlinear function of power in an attempt to reward higher intensity appropriately. In Coggan's very popular TSS (training stress score) point system, 100 points corresponds to a 1-hour time trial done at 100% effort, although you can earn those same 100 points by doing intervals at higher power or longer rides at sub-threshold power. Power-based point systems have a number of advantages. As a measure of intensity, power is completely non-subjective, and can be correlated with physiological variables such as lactate ion concentration. The availability of power meters for bicycles means that data collection is automated and fairly simple. There are a number of different software programs and websites that can perform not only the point calculations, but also the impulse-response modeling of the training plan, and even the construction of a training plan. In principle, power is fairly transferable to different sports. Generating 200 W while swimming would earn you the same number of points as generating 200 W while cycling. Unfortunately, it is difficult to measure power output directly while swimming, and there are no commercial devices that swimmers can use to collect power data. Speed There is no equivalent of a power meter for swimming (or running), but it is easy to measure swimming speeds or swimming times. Because there is a known relationship between velocity and power, times can be used to estimate power, which can then be converted to points of some sort. Skiba's SwimScore is one such method, that performs a weighted average power over a workout using swimming velocities. It is a complex calculation (with several ad hoc assumptions), but there is software commercially available to perform the calculations. In this system, 100 points corresponds to a 3000 m time trial swum at 100% effort. There is a marginal attempt to keep these points comparable to those from Coggan's system (although this is flawed for anyone who swims 3000 m considerably faster or slower than 1 h.) On this forum, qbrain has posted another point system that uses velocity as a proxy for power. The intensity used to calculate his "energy points" is merely velocity cubed, which is propotional to power. This calculation is fairly simple: each rep earns a certain number of points based on the interval time, with no weighted averages required. For example, you'd earn 100 points for every swimming 100 SCY in 1:27, while swimming 100 SCY in 1:02 would earn you 200 points. These points are not easily transferable other sports, however.