Cross-Training for Runners

Originally Published in: Techniques Magazine

Provided by: USTFCCCA

Running has long been one of the most popular, simplistic and enjoyable ways to exercise for all age groups. Running is a sport that can be practiced for a lifetime and provides benefits ranging from improved blood pressure, weight loss, mental health, muscle strength, heart and lung function, and of course, improved running performances. But despite these benefits, some evidence suggests that up to 79 percent of runners report injuries or pain in a one year period (van Gent et al., 2007). Overuse injuries make up the majority of these injuries and have been linked to the high impact nature of running (Hreljac et al., 2000 & Hreljac, 2004; Davis et al., 2016).

For runners with a few years of training under their belt, missing a few weeks of training or having to skip some key workouts due to injury can greatly limit their success. Indeed, as little as two weeks of training cessation can have deleterious effects to a runner's aerobic fitness (Mujika, 2000; Doherty et al., 2003). At the elite level, since financial security comes with high levels of performance, missing important training periods due to injury can be quite costly. For this reason, many injured runners will continue training using cross-training modalities that do not exacerbate the symptoms or worsen the injury in order to prevent or attenuate the losses in fitness while unable to run.

CROSS-TRAINING

Various types of low-impact cross-training modalities can help maintain aerobic fitness during periods of injury. Cross-training can also be used to supplement running training to increase training volume without the increased associated impacts of running. It may also be used to aid in the recovery process following heavy training periods or following strenuous training sessions, again, by avoiding large impact forces during running. Proponents of the "Go Big or Go Home" training philosophy have viewed the incorporation of cross-training in a training program as a less than optimal approach.

However, scientific research has provided substantive evidence that cross-training can prevent or reduce the losses in fitness as a result of running training cessation. To use a recent anecdotal example, American long distance runner Emily Infeld qualified for the Olympic Games in two events (5,000m and 10,000m) after being diagnosed with a femoral stress fracture early in the year and having to take a substantial step back from her regular running training. Infeld spent many hours per week cross-training to maintain her fitness until she was able to resume her running-specific training in preparation for the U.S. Olympic Trials. Evidently, for some, cross-training has highly impactful training benefits. With numerous low-impact cross-training modalities available, runners and coaches often want to know what is the best form of cross-training for runners?

We broke down the different modes of cross-training in two categories: 1) non-running-specific cross-training (i.e. movements are vastly different than running) and 2) running-specific cross-training (i.e. movements more closely replicate those of running).

NON-RUNNING-SPECIFIC CROSS-TRAINING

The most popular forms of non-running-specific cross-training modalities include cycling, swimming and rowing. Cycling is a type of exercise most runners know how to do or have done in the past and, is easily accessible for most (i.e. most fitness gyms have stationary bicycles and many runners own bikes). Cycling-only training has been found to maintain aerobic fitness in recreational runners (Moroz et al., 1987), and when combined with running, cycling can improve running performance (Mutton et al., 1993; Flynn et al., 1998).

However, the motion of cycling differs greatly from running as it places the knee and hip joints in much more flexed positions compared to running. These greater joint flexion positions during cycling change the contraction lengths of muscles involved. These different joint positions and muscle lengths, during cycling appear to subsequently alter stride mechanics and, torso, pelvis and hip motions immediately following cycling (Cala et al., 2009, Rendos et al., 2013). Further, prior cycling bouts reduces the 10 km running performance in triathletes (Tew, 2005) although, anecdotally, many triathletes have seemingly posted much better running times within a triathlon event compared to individual running races - we will leave that curious phenomenon alone for now. Although we observe changes in running biomechanics immediately following cycling, the long-term effects of cycling on running mechanics are unknown. Until we know more on these long-term effects, if runners choose to cycle as a mode of cross-training, it may be smarter to complete their run first (if they are uninjured) before cycling.

SWIMMING HAS BEEN A GO-TO CROSS-TRAINING METHOD FOR MANY YEARS.

Swimming offers a non-impact exercise that rarely aggravates a runner's injuries. Nonetheless, from a biomechanical perspective, the specificity of swimming is the most unlike running. Swimming is performed in a horizontal position in a nearly weightless environment due to water's buoyancy forces. This greatly changes muscle recruitment patterns compared to running and underloads musculoskeletal tissue. This under-loading can, over time, reduce bone density which can increase the risk of skeletal stress fractures as a result of chronic tissue loading. For this reason, if runners are unable to run without pain, it may be more optimal to include weight-bearing cross-modality exercise such as cycling or elliptical training in addition to swimming. Scientific evidence on the impact of swimming training to improve running performance is limited. Some research shows that, due to increased stresses on the respiratory system, swimming training can improve running economy (i.e., "fuel economy") in non-runners (Lavin et al., 2015). In essence, the respiratory system becomes more efficient from swimming training and in turn, improves "fuel economy" during running. But frankly, if your runners are not the best swimmers, it may be more effective to have them cross-train using a different modality (for safety and frustration reasons).

Rowing ergometry (i.e., indoor trainer) is another cross-training alternative that is accessible for most. Rowing, unlike swimming, is performed under weight-bearing conditions and requires use of the upper and lower body muscles (Hosea & Hannafin, 2012). However, during rowing, as in cycling, the athlete is seated which does not stimulate the weight-bearing conditions on the legs as while running. The upper body pulling motion in combination with the lower body pushing motion engages back and upper and lower limb muscles. These different motions compared to running may provide some aerobic benefits due to use of certain muscle groups that are minimally used in running.

Although cycling, swimming and rowing do not simulate specific running motions, they all provide aerobic benefits and strengthening of muscles that are generally under-utilized during running. This introduces some variability in training which can certainly have positive outcomes with regards to injury prevention in runners. One potentially harmful aspect of running is its repetitive nature which cyclically loads the same tissues at the same locations under large impact forces. Think about hitting a piece of wood with an ax continuously in the same location compared to changing the location of the strike. When you strike the piece wood in the same location, you will break it much more quickly than if you change your strike location. The same concept can be applied to running with regards to cyclical tissue loading. By incorporating cross-training that yield different movements compared to running may not necessarily be detrimental, at least from an injury risk perspective.

RUNNING-SPECIFIC CROSS-TRAINING

The "Law of Specificity" states that an athlete will benefit from training that is specific to their sport. Time and energy spent training with non-specific cross-training for trained runners will have some positive effects (after all, some training is better than no training) but may not be as beneficial for a runner compared to more running-specific cross-training. Three "running-specific" modes of cross-training for runners include the stationary elliptical, elliptical bicycling and water running.

STATIONARY ELLIPTICAL TRAINER

The stationary elliptical trainer was introduced in the early 1990s, and this exercise machine is found in almost all fitness centers and rehab facilities across the United States. It consists of two ellipse-moving pedals and although it is a weight-bearing exercise, it produces no impacts (i.e., no collision between the feet and pedal surfaces).

Research on stationary elliptical trainers in untrained college students shows similar metabolic cost (i.e., oxygen used during exercise) between treadmill running and elliptical exercise (Brown et al., 2010). This research suggests treadmill running and elliptical exercise have the same impact on running "fuel economy" in untrained non-running young adults. More recent research, however, shows lower "fuel economy" during elliptical exercise compared to treadmill running in men and women who ran at least 20 miles per week (Chester et al., 2016). This finding suggests that in (at least recreationally trained) runners, elliptical exercise may not provide as high aerobic stimulus as running, albeit, on a treadmill. In fact, four weeks of elliptical training only in high school runners resulted in lower 3,000m time trial performance compared to running training only (Honea, 2012). When elliptical training was used as supplemental training (i.e., easy run days replaced by elliptical training) in high school cross-country runners over a four-week period, changes in "fuel economy" and 3,000m performance following training were not different between supplemental elliptical training and running only (Paquette et al., 2016). These findings suggest that stationary elliptical training could be used instead of "easy" running miles in high school runners, if necessary (e.g., runners with history of injuries) but may not be an effective cross-training modality to maintain fitness without any running training. There is currently no available research on the effects of elliptical training in injured runners but runners with injury symptoms that are exacerbated by the ground impacts of running may obtain training benefits from elliptical exercise if they sustain a moderate to (mostly) high intensity during training.

Further, elliptical exercise yields lower limb biomechanics (movement) that are different than running. Specifically, elliptical exercise produces much larger quadriceps (Prosser et al., 2011; Rogatzki et al., 2012) and back extensor (Rogatzki et al., 2012) muscle activation along with continuous knee extension or straightening of the knee while weight-bearing as opposed to flexion or bending observed in running (Rogatzki et al., 2012; Chester et al., 2016). The straightening of the knee while weight-bearing is accomplished via concentric quadriceps muscle action, or shortening of muscle under tension. In contrast, the knee flexion during the weight-bearing portion of running is accomplished via eccentric quadriceps muscle action, or lengthening of muscle under tension. Although you may not be familiar with the term "eccentric quadriceps muscle action", you may be quite familiar with its effects on your quadriceps during a long run or marathon and more specifically, in the days following these runs. Eccentric muscle actions are much more damaging to muscle fibers compared to concentric muscle actions. As a result, eccentric muscle actions play a large role in the development of delayed onset muscle soreness, or DOMS. Since the muscle action is different, a return to running following extended periods of "elliptical training-only" may at first be quite "shocking" to lower extremity muscles such as the quadriceps. Coaches and runners should consider these bio-mechanical differences with regards to how quickly they can increase running volume when coming back from periods of cross-training. Although the stationary elliptical has training and potential rehabilitation benefits, many runners find it unbearably boring to spend hours cross-training on an indoor elliptical machine while injured.

ELLIPTIGO

One of the latest cross-training options is the ElliptiGO, a combination of a bicycle and an elliptical machine that allows users to train outdoors just as they would on a bicycle. Similar to a bicycle, the ElliptiGO has handlebars, gears and brakes and a step length of 25 inches. Although this is over 10 inches shorter than a typical step length during slower running (Peterson et al., 2015), it is 7 to 9 inches longer than most stationary elliptical trainers. In addition to a longer step length compared to stationary elliptical trainers, the ElliptiGO motion allows the foot to recover through the stepping motion in a downward angled position, similar to running.

U.S. Olympian Meb Keflezighi, who since beginning to incorporate the ElliptiGO into his training has remained injury free and recently competed in his fourth Olympic Games. The efficacy of ElliptiGO training is also beginning to be supported by scientific research. Earlier this year, a research study conducted at Ohio University showed no physiological or 5,000m time trial performance changes between ElliptiGO-only and running-only training over a four-week period (Klein et al., 2016). Training was matched for total training time, frequency, intensity and terrain. The study also showed that a subjective rating of enjoyment was not different between ElliptiGO and run training but, subjective ratings of lower body muscle soreness were lower during ElliptiGO training. The studys conclusions were that ElliptiGO training yields similar fitness and performance benefits as running training but with lower associated ratings of muscle soreness during training. Although the study was done on trained collegiate runners, results are promising for all types of runners. For example, during periods of planned rest from running (e.g., following a competitive season), athletes and coaches could take advantage of such cross-training benefits to maintain fitness without the high impacts and muscle damage caused by eccentric muscle actions during running. However, it is important to remember that many athletes need time off not only to allow physical but also, mental recovery following long competitive seasons. Taking a full break without any planned training is often necessary.

New research aimed to answer the question of which cross-training modality was most optimal for "fuel economy," time trial performance and, mobility, in high school cross-country runners (Paquette et al., 2016). This study was novel in that it included four weeks of cycling, stationary elliptical trainer and ElliptiGO cross-training to replace two easy runs per week instead of completely replacing running training. The study, for which the results were presented at the annual meeting of the American College of Sports Medicine, showed improvements in 3,000m time trial performance for all cross-training groups that were similar to running-only training. This finding suggests that replacing two easy runs per week with cross-training does not affect running performance. Coaches can take advantage of this result with athletes who are more injury prone than others. The most interesting findings from this study, however, were that only the ElliptiGO group of runners improved their "fuel economy" and lower limb joint mobility after the four-week training period. These benefits of ElliptiGO usage to replace easy runs may be related to the stability requirements of the ElliptiGO. When riding the device, users must use certain muscles to stabilize their core (i.e., shoulders, torso, hips) to balance their whole body while pedaling. This stability requirement may have a training effect on muscles that are under-utilized during running, cycling and, stationary elliptical training. Future work on muscle activation requirements between modalities will shed more light on the mechanisms responsible for training benefits. Since stationary elliptical trainers and the ElliptiGO are forms of non-impact cross-training they both may be helpful to runners whose injury symptoms are intensified by the impact associated with running. For runners whose injury symptoms are unbearable while weight-bearing (e.g. elliptical), the impact-less reduced gravity (i.e., body weight) environment provided by water running is often the only option.

WATER RUNNING

Water running has been a popular mode of cross-training among runners for many decades since it allows runners to very closely replicate the running motion without the high impacts and weight-bearing aspects of running. Water running can be performed in shallow water where a runner can still use the ground to propel themselves forward against the water's resistance. Deepwater running - sometimes while wearing a flotation belt - is performed in water depths that do not allow ground contact while runners attempt to move their arms and legs in motions similar to land running to stay afloat and moving forward. Just like swimming, deep water running does not provide the normal tissue loading conditions of weight-bearing exercise and coaches should incorporate supplementary weight-bearing exercises to avoid overuse injuries when they return to running.

There has been extensive research conducted on the effects of water running on running fitness and biomechanics. Research suggests that water running is an effective mode of cross-training to maintain aerobic fitness after up to six weeks of training in trained endurance athletes (e.g., competitive and cross-country runners) (Wilber et al., 1996; Bushman et al., 1997; DeMaere and Ruby, 1997). Similar to elliptical training, water running does not produce the same maximal physiological demands observed during running (Dowzer et al., 1999) suggesting limited maximal aerobic stimuli from these cross-training modalities. From a biomechanical perspective, different muscle activations and lower limb joint motions have been observed between deepwater and over-ground running (Killgore et al., 2006; Kilding et al., 2007; Masumoto et al., 2013). These biomechanical differences have the same implications as elliptical training with regards to returning to running training following extended periods of cross-training (i.e., different primary muscle actions). Similar to stationary elliptical trainers, water running can be quite mind-numbing in the confines of a 25 or 50m pool. That being said, many runners enjoy water running and the enjoyment aspect of cross-training on an individual basis should not be overlooked.

CONCLUSION:

Whether you can't run or are seeking ways to enhance your training regimen with some cross-training, remember not all forms of cross-training are created equal. Assess your needs and choose what works best. Adding cross-training to a runner's training has clear benefits and research suggest that modalities that produce running-specific movements may be more optimal. That being said, incorporating cross-training that produce nonrunning-specific movements can increase the variability of the training regimen and could have injury prevention implications. Some modalities may produce greater training benefits, or more "bang for your buck," than others and coaches should without a doubt consider scientific evidence to support their choices. Finally, although the physical training benefits of cross-training should not be ignored, we urge coaches to not forget about the mental or psychological aspect of cross-training for your athletes. If you notice that certain types of modalities provide a much greater enjoyment during training which allows athletes to "regroup" or "recharge" from the constant hard work that comes with running training, then by all means, take advantage of that.

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Ian Klein is an anatomy and physiology lecturer in the Department of Biological Sciences at Ohio University and a researcher in the Clinical Translational Research Unit (CTRU). He is also an exercise physiologist/volunteer coach for the Ohio University men's and women's cross country teams and women's field hockey team.

Max Paquette is an assistant professor at the School of Health Studies at The University of Memphis and the director of the Sport And Health Consulting Center (SPAHCC). He has published over 30 scientific research articles focused on lower limb biomechanics of human movement. He also coaches competitive and elite high school and post-collegiate middle-distance runners and former Canadian Olympic Trials finalist in the 3,000m steeplechase.