A Comparison of Negative Joint Work and Vertical Ground Reaction Force Loading Rates in Chi Runners and Rearfoot-Striking (RFS) Runners.
Goss and Gross, 2013.
Journal of orthopaedic & sports physical therapy | Volume 43 | Number 10 | October 2013 | 685
This is a timely study with a lot of focus on bare foot and minimalist style running shoes in the media of late. The study attempted to compare “chi runners” – a style of running focused on a non-rear foot strike pattern, high cadence and shorter stride length (see table) – with a rear-foot strike (RFS) pattern of running. The rear foot strike pattern is one that is commonly seen in runners and has been hypothesised as being a major cause of running related injuries due to the increased vertical ground reaction force loading rates and increased knee loads. It has been proposed that “chi-running” reduced knee joint loading and ground reaction force loading rates.
TABLE 1 Visual Criteria Used to Determine Chi Running Style*
|1. Postural alignment in mid-stance: shoulders, hips, and ankles aligned|
|2. Hips slightly ahead of feet in mid-stance|
|3. Knees bent on impact: no heel striking or dorsiflexion|
|4. No contraction of calves in terminal stance: no toe-off|
|5. Lifting ankles, not knees: knees are bent but not lifted|
|6. Pelvic rotation more prevalent than upper-body rotation|
|7. Arm swing rearward|
|8. Elbows bent 90°: not pumping|
|9. Not bending at the waist in mid-stance|
*Chi runners were required to demonstrate the first 5 criteria.
Commentary of Results
Result of the study concluded that RFS runners have significantly:
- Higher amounts of work at the ankle dorsi-flexors (muscles pulling the ankle upwards)
- Higher amounts of work at the quadriceps (muscle at the front of the thigh) compared to “chi runners”.
- Greater amounts of knee movement during the time the foot was on the ground i.e. knee moving inwards.
- Less steps per minute with higher “braking” forces than the “Chi runners”.
Real world Implications
This means that the muscles at the front of the shin and the muscles at the knee are working harder in the RFS group than the “chi running” group. This may lead to more compression at the knee (tibio-femoral) joint and the knee cap (patella femoral) joint. Other studies have demonstrated less compressive joint force at the patella joint in “Chi runners”. This could result in less pressure on your cartilage and knee joints that may reduce the risk of injury to these areas whilst running.
It has also been observed in other studies that higher braking forces are associated with medial tibial stress (shin splints) and tibial (shin) stress fractures. Therefore if this is an injury you have suffered it could well be worth learning to run with a forefoot strike to reduce these loads.
A step frequency of >/= 180 steps per minute is often seen in elite standard runners or at least runners of considerable experience. This number of steps is seen as desirable due to it reducing the contact time that ones foot is on the ground. The less time you are on the ground the less time there is for your hips, knees and ankles to go into positions that are less than favorable. From personal experience working with clients I have seen significant improvements in pelvic drop angles and knee rotation just by increasing their cadence (steps per minute).
Other results concluded that “Chi runners” have:
- No ankle dorsiflexion negative work
- Increased ankle plantar flexion (calf muscle) work
- Reduced average vertical loading rates
Real world Implications
The muscles at the front of the shin of “chi runners” don’t work to slow the foot down – this may lead to reduced load on the shin bone and reduce the incidence of shin splints (MTSS). The increased work for the calf muscle means that caution needs to be applied when starting this style of running as it will mean more load on the Achilles tendon and calf muscle. The risk of developing Achilles tendon pain or a muscle strain is higher and thus you need to start with low mileage and build steadily week after week. Likewise, if you have ever had fractures in your foot bones at the front of the foot then you need to exercise caution with learning to run with a “chi” style. The reduced average vertical loading rates seen in “Chi running” may have implications with people who have suffered from shin fractures, plantar fasciitis and patellofemoral pain syndrome (pain at front of knee). If you have suffered from these conditions/injuries then learning to run with a forefoot strike may prove to be beneficial.
More information required
From what we are seeing with research into different running styles is that there is still a significant amount of work required to determine what all of this data means. There is no definitive data saying that if you run forefoot or “chi” style that you will not get injured. As highlighted, the forefoot running can increase load onto other areas that may also be at risk of injury. From my own experience, forefoot running has been a revelation and immensely helped my knees. My advice would be if you are struggling with running injuries then get your running style analyzed by a physiotherapist and the go about correcting the issues discovered.
The study consisted of a fairly evenly matched selection in terms of body characteristics of experienced runners in their own technique, with at least 6 months experience and a minimum running distance of 19.2 km/ per week. The groups consisted of 22 RFS runners and 12 “chi runners”. The chi runners were selected by the creator of Chi Running – Danny Deyer – who actually excluded 11 runners from the Chi running group because they did not match the criteria specified above. He was blinded to this choice 17 months later and still managed to choose the same 12 chi runners, this added some reliability to the “chi running” criteria. The runners were all allowed to self select their running speed on the treadmill and also wear the shoe of their choice when being tested. Interestingly, all 22 RFS runners and 5 “chi runners” chose to wear traditional running shoes i.e. defined as motion –control stability or cushioning with a drop of 10mm or greater from heel height to toe, while 5 chi runners wore “minimalist” shoes i.e. very flexible, minimal support and a heel-to-toe drop of 4mm or less. The collection of data was standardized for all runners using an instrumented treadmill with a force plate sampling at a very high rate to ensure adequate data capture. They also utilized a high spec 3-dimensional motion analysis system called Vicon Nexus.
The use of a treadmill is the first obvious weakness of this study yet unfortunately one that is difficult to avoid in order obtaining the necessary information. People who normally run outdoors can change their running style when placed on a treadmill. The stride frequency (number of steps taken per minute) was seen to be quite high in both groups (RFS = 173-180 vs Chi = 175-195). This cadence is quite normal in “chi running” yet not always seen in RFS running where typical cadence has been reported to be typically at 150-160 steps per minute. There was also half the number of “chi runners” studied than the RFS group.
These are just my thoughts and views.
Scott Tindal MSc (SEM, London) MCSP