Although you have an individual current mileage limit, this limit changes over time. The mileage that contributed to your shin splints 5 years ago will not necessarily cause problems for you again. You need to be a good detective and figure out the causes of your past injuries. Many runners say, “I tried high mileage once years ago, and I just got tired and hurt,” and they permanently return to what they consider to be their safe mileage range. They don’t consider that in the ensuing years their bodies may well have gained the ability – and their minds the wisdom – to handle higher mileage and to reap the concomitant benefits.
An important determinant of marathon performance is running economy at marathon race pace. Although some evidence shows that economy improves with training, no one fully understands the secrets of improving running economy. Various studies have found running economy to improve with weightlifting, biofeedback, relaxation training, hill training, exhaustive distance running, speed work, and long intervals. Jack Daniels (2005) recommends running fast intervals to reduce wasted motion and to train the body to recruit the most effective combination of muscle fibers. A variety of biomechanical factors, such as a narrow pelvis, small feet, and “faster rotation of shoulders in the transverse plane,” have been suggested as contributors to running economy.
Throughout this book, we’ll prescribe specific intensities for various types of workouts to help you prepare most effectively for the marathon. Heart rate monitors are a useful tool you can use to check the intensity of your training. Training intensity can also be described in terms of speed, but unless you train daily on a track or measured stretch of road or run with a GPS, you don’t really know how fast you’re training most of the time. Monitoring the intensity of your training in terms of heart rate, however, is simple.
The intensity of your runs can be stated relative to your maximal heart rate or as a percentage of your heart rate reserve. Your maximal heart rate is, quite simply, the fastest that your heart will beat during maximal-effort running. The most accurate formula for estimating maximal heart rate is 207 minus.7 times your age. Using this formula, a 43-year-old would have a predicted maximal heart rate of 177 [207 – (.7 × 43)]. Because of the variability between individuals, however, your actual maximal heart rate may be more than 10 beats per minute higher or lower than your predicted maximal heart rate. Using an estimated maximal heart rate, therefore, can lead you to train too hard or not hard enough, so it’s better to do a performance test to determine your actual maximal heart rate.
You can find your maximal heart rate quite accurately during a very hard interval session. An effective workout is to warm up thoroughly and then run three high-intensity 600-meter repeats up a moderate hill, jogging back down right away after each one. If you run these 600s all out, your heart rate should be within two or three beats of maximum by the end of the third repeat.
Heart rate reserve is an even more accurate way of prescribing training intensities because it takes into account both your maximal heart rate and your resting heart rate. Your heart rate reserve is simply your maximal heart rate minus your resting heart rate, and it reflects how much your heart rate can increase to provide more oxygen to your muscles. By resting heart rate we mean your heart rate when you first wake up in the morning. As an example of calculating heart rate reserve, Scott’s current maximal heart rate is 188 and his resting heart rate is 38. His heart rate reserve, therefore, is 188 minus 38, which equals 150 beats per minute.
To calculate the proper heart rates for a workout using heart rate reserve, multiply your heart rate reserve by the appropriate percentage, and then add your resting heart rate. For example, as a highly experienced runner, if Scott wanted to do a lactate-threshold workout at 82 to 88 percent of his heart rate reserve, he would stay in the range of 161 [(heart rate reserve of 150 ×.82) + resting heart rate of 38] to 170 [(150 ×.88) + 38] beats per minute. This compares closely to using 86 to 91 percent of his maximal heart rate, which would put him in the range of 162 to 171 beats per minute.
The prescribed training intensities used in this chapter and chapters 3 and 7 are summarized in table 1.2. These intensity ranges are appropriate for most experienced marathon runners. Less-experienced runners should generally train at the lower end of the recommended ranges, while elite runners will generally be at the high end of the ranges.
During a lactate-threshold session or long run, your heart rate will tend to increase several beats per minute even if you hold an even pace. On a warm day, your heart rate increases even more because of dehydration and as your body sends more blood to your skin to aid in cooling. This phenomenon is discussed in greater detail in chapter 2. The implication for your lactate-threshold sessions and long runs is that you should start these sessions at the low end of the specified intensity zone and allow your heart rate to increase to the high end of the zone during the workout.
On a low-humidity day with temperatures in the 70s (low 20s), increase your zones by two to four beats per minute to gain the same benefits as on a cooler day. On a high-humidity day in the 70s (low 20s) or a low-humidity day in the 80s (high 20s to low 30s), increase your zones by five to eight beats per minute. On a high-humidity day in the 80s (high 20s to low 30s), just take it easy (Lambert 1998).
According to Don Morgan, PhD, who has conducted a large number of studies on running economy, the most important factor for improving economy may be the number of years (and accumulated miles) that you have been running rather than the specific types of workouts that you do. The mechanism for improvement may be that with training your fast-twitch muscle fibers gain more of the characteristics of the more economical slow-twitch fibers. Morgan speculates, however, that different types of training may improve economy depending on the specific strengths and weaknesses of the individual athlete. This individuality in response may explain why no clear consensus exists on how to improve running economy.
As with most aspects of running, there are no guarantees, but the following guidelines will help you increase your mileage without getting injured or overtrained:
• Bite off small chunks. Over a few years,you can double or triple your mileage, but increasing mileage too much at once is almost certain to lead to injury or overtiredness. Unfortunately, there’s no scientific evidence indicating how great an increase over a given period is safe. A commonly used, but unvalidated, rule of thumb is to increase mileage by a maximum of 10 percent per week. Jack Daniels (2005) recommends increasing mileage by no more than 1 mile (1.6 km) for each training session that you run per week. For example, if you run six times per week, you would increase your mileage by up to 6 miles (10 km) per week.
• Increase in steps. When charting new territory, don’t increase your mileage week after week. That approach is very likely to lead to injury. Instead, increase your mileage 1 week, then stay at that level for 2 or 3 weeks before increasing again.