Running itself is the cardinal component of the distance runners program, though a large volume of running at race pace is definitely not desirable: it creates substantial stress, generating a catabolic state and a high risk of injury. The optimal program incorporates a high volume at low intensity and a small volume of high intensity training. If your goal is to achieve longevity as a successful distance runner, it is essential to have a strategy that allows a high volume of training without accumulating too much damage to the body, especially to the leg muscles and joints. Some runners can achieve the required high volume of low intensity training purely with low intensity running. For many, the optimum strategy includes a substantial amount of low-impact aerobic cross training.
The principle virtue of low impact cross training is that it avoids the potentially damaging eccentric contraction at foot-fall. This allows large volume with minimal risk of injury. The limitation is that it fails to develop the powerful eccentric contractions that are essential for getting airborne, a cardinal feature of running. In contrast, plyometric cross-training is designed specifically to generate eccentric contractions and is even more effective than running itself for developing the type 2 a fibres that play a major role during eccentric contraction, but it carries even greater risk of injury.
Forms of aerobic cross training
Aerobic cross training can take many forms. One important distinction is the distinction between weight-bearing exercise, such as elliptical cross training, stair-stepping or various devices designed to closely mimic the action of running, such as the Zero Runner and Bionic Runner; or non-weight bearing exercise such as cycling, aqua-jogging and swimming. Another distinction is based on intensity: ranging from the low aerobic zone via the upper aerobic to the anaerobic zone. I will focus on weight-bearing aerobic cross training, with the main emphasis on training in the low aerobic zone, but I will include some comments on moderate and high intensity cross training.
The specific goals of low intensity aerobic cross training are:
- Enhancing fat metabolism, through development of the enzymes that perform beta-oxidation of fat.
- Enhancing the shuttling of lactate between type 2 muscle fibres and type 1 fibres which have a large capacity to utilise lactate as fuel. Note that even in the low aerobic zone, lactate is produced in type 2 fibres, but because it is taken up into type 1 fibres it does not spill over into the blood stream.
- Developing capillary supply to muscle.
- Developing cardiac endurance.
- Strengthening connective tissues and bones providing protection against injury.
- Development of postural muscle endurance.
Although weight-bearing offers beneficial musculo-skeletal strengthening that helps protect against injury this can be a disadvantage during recover from injury, and in such instances either cycling, aqua jogging or swimming might be preferable. I will discuss these forms of cross-training in a subsequent post.
Elliptical Cross trainer
The elliptical cross-trainer is designed such that the two feet follow an elliptical trajectory while pressing on two moving platforms to drive a flywheel, and the legs move in manner that is somewhat similar to the action of running. The main driving power is generated by extension of hips and knees, as in running. However the degree of flexion of hips and legs is less than when running at moderate or fast paces. There is little or no plantar flexion of the ankle or rotation of the hips. Nonetheless the elliptical does help develop the hip and knee extensors that are the powerful drivers of running. There is potential for development of capillaries, fat metabolism and the shuttling of lactate between type 2 and type 1 fibres in these muscles, with minimal risk of damage.
Although it is possible to use the arms to assist in driving the flywheel via two handles, I prefer to avoid using the handles, except when aiming for very high power output. I aim to swing the arms in the same manner as when running, thereby using the upper body to help generate the force exerted through the legs, in the same manner as when running. This promotes development of the core muscles required to maintain a good running posture.
As with all forms of low impact cross training, the elliptical has the potential to develop cardiac output and cardiac endurance.
One potential disadvantage of a stationary elliptical is boredom, though in fact I find that low intensity elliptical sessions create a positive meditative state and foster a helpful awareness of the relationship between breathing and the rhythmic action of the legs.
I use the elliptical regularly as an adjunct to my training. During base-building, typically 30% of my training is on the elliptical. On one occasion, over a decade ago, when I had done only a very small amount of training in the preceding 6 months, I did 6 weeks of training exclusively on the elliptical. I did 6 half-hour sessions per week, including a mixture of low aerobic and mid-aerobic sessions. Before the start of the 6 week elliptical block I had done a timed 6 Km run at lactate threshold pace. I repeated this running session after the block of elliptical training and was pleased to note that my pace was 12% faster and average heart rate slightly lower than before the elliptical training. It appears that at least under some circumstances exclusive elliptical training can result in a substantial improvement in running speed at lactate threshold. However at that time, I was quite unfit and I would have anticipated an appreciable improvement in running performance from virtually any systematic program of aerobic training.
I also employ the elliptical for high intensity interval training. Even when starting from a fit baseline, I have experienced substantial gains in aerobic capacity when elliptical HIT sessions have been my only form of high intensity training. In fact since injuring my knee in an accident a year ago I have been forced to restrict the amount of high intensity running I do, and have found the elliptical invaluable for high intensity training.
There are noteworthy examples of elite athletes employing elliptical training during recovery from injury. In the months prior to the Beijing Olympics Paula Radcliffe was unable to run on account of a stress fracture of her femur, and used the elliptical on account of its low impact. In the Olympic marathon she maintained a place in the leading group until 30 Km, demonstrating that her aerobic fitness was good, but beyond that point her legs gave way, causing her to drop back to a disappointing 23rd place, confirming that elliptical cross-training does not condition the legs adequately to sustain a high level of performance for the entire duration of the marathon.
More recently, 10,000m runner Emily Infeld experienced a stress fracture of her left hip three months before the US trials for the Rio Olympics. She employed a seven week program of cross training that included elliptical training and swimming, before resuming regular running. In the trials, she was second to Molly Huddle , in 31:46.1. Six weeks later, in Rio, Molly was 6th and Emily 11th in 31:26.9.
The Elliptigo is an elliptical cross trainer on wheels. It provides very similar fitness benefits to those proved by the elliptical, with the added advantage of being outdoors on the open road. Its main disadvantage compared with the elliptical is the cost.
Elites including Dean Karnazes and Meb Keflezighi have used it to augment their training. Both have been sponsored by the manufacturer of Elliptigo. Following his victory in the 2014 Boston Marathon, Meb reported that the Elliptigo was a useful way to maintain fat burning capacity, with minimal stress on his legs. In the 2016 US Olympic marathon trials, Meb finished second in 2:12:20 behind Galen Rupp, and made it to his 4th Olympics at age 40. In Rio, he finished in 33rd place, in 2:16:24. This can be compared with his silver medal performance of 2:11:29 in Athens, 12 years earlier. He considers that Elliptigo cross-training has contributed to his remarkable longevity at elite level.
The Zero runner is a stationary machine, somewhat like the elliptical, but with several extra hinges, including hinges at knee height in the rods from which the foot platforms are suspended. The hinge allows a much greater flexion of the knee than the elliptical, and thus provides an action that more closely resembles the movements of running. Dean Karnazes reports that the motion is smooth and natural and feels just like running, but without the impact. As with the Elliptigo, the disadvantage is cost.
The Bionic Runner employs an action designed to mimic the action of running, but without impact, perhaps even more closely than the Zero-runner. It has the added advantage that it is not stationary and is intended for outdoor use. It has two wheels like a bicycle but is ridden standing up. The cranks are constructed in manner that achieves a foot trajectory very similar to the trajectory when running. In particular, the ratio of swing to stance duration mimics the shorter stance phase typical of moderate or fast paced running. The recruited muscles are similar to those recruited when running, though it appears to me that the balance of work done by the extensors of the knee relative to the extensors of the hip is somewhat greater for the Bionic Runner than for running. It also places a substantial demand on the postural muscles of the torso. It lends itself naturally to moderately intense aerobic training. (I am grateful to Ewen for drawing my attention to the Bionic Runner)
The kick-bike scooter is a two-wheeled device propelled by pushing against the ground with a single leg, with an action that engages many of the muscles employed in running. The range of motion at the hip is potentially large, thereby providing a good work-out for the hip extensors, especially gluteus maximus. It also provides far greater exercise for the calf than the elliptical. Because it engages a large number of muscles, it tends to encourage a more vigorous workout than many other forms of low impact aerobic cross-training.
A stair stepper offers the advantages of hill training with minimal impact. It provides a vigorous workout for the glutes, quadriceps, hamstrings and calf muscles, and also for the heart. Kelly Holmes made great use of a stair stepper in preparing for her double victory in the 800m and 1500m in the Athens Olympics.
All forms of weight-bearing, low impact cross training offer the possibility of enhancing cardiac and leg muscle function in a manner that minimises risk of musculo-skeletal damage. Some forms, such as the Bionic Runner, kick-bike scooter and stair stepper are more readily adaptable to enhance muscle power and cardiac output, while others such as the elliptical, Elliptigo and Zero-runner lend themselves to developing endurance, though these differences are only a matter of degree. In practice, the optimum choice of type of aerobic cross training is likely to depend on issues of preference and convenience, such as the choice between indoor and outdoor, and on practical issues such as the cost or availability of the equipment.
In general, weight-bearing forms of cross training provide a good opportunity to develop endurance of the core muscle essential for good running posture. The elliptical, the stair-stepper and perhaps the Zero runner allow an upper body action that closely resembles the upper body action when running, but in all forms of weight bearing cross training, it is important to focus on good posture for maximum benefit.