Ok, I know, I know...I work diligently to keep this blog rooted in research and outside of the realm of speculation. That being said, I think it is clinical expertise and observation that continue to drive in-depth research topics. I was having one of these moments recently on a run, when I do most of my introspection. The question I pose: is there a window of opportunity when a new runner is most likely to begin experiencing injury?
I've been putting some thought into this, trying to connect what I know about the science and what I commonly see in the clinic. I'm hoping this post will help newbies steer clear of injury, and start some good conversations in the clinics. The framework I'm working within is that of the typical, fair-weather runner, who makes the choice to take their running to the next level and go after a 10k, marathon or half marathon: a distance that's new and challenging. Some of the runners who fit this description are likely to not make it to the starting line, or at least without some injury along the way.
what we know about running injuries
Research tells us that many of the overuse injuries sustained in the process of preparing for a race are not sustained in the first month, nor on race day exclusively. They tend to occur somewhere later in the typical 14 week time frame, especially as those long runs begin to increase in distance. For the sake of this post, I'm speaking almost exclusively of 'overuse injuries' rather than acute onset injuries related to sprains, strains, and falls.
The old-school typical attitude toward this follows an archaic understanding of the research literature which directly correlates higher mileage weeks and longer race distances with higher injury rates. Much like the physician I encountered for some knee pain in 2005, many docs will still respond by saying 'don't run so much,' 'running is bad for your knees,' or 'humans were never meant to run that far.' I totally don't buy this argument and see it largely as a clinical cop out. Research has overwhelmingly praised the benefits of distance running, and ended these myths. Fixing runners is difficult and typically not the area of expertise for most family physicians.
consider the training in stages
I have some thoughts on what may be some common contributing factors. First, cardiac adaptation. Those first 4-6 weeks of training, especially for someone who is new to running or prolonged cardio activity, the biggest limiting factor in runner is the cardiovascular system. This includes everything from the blood volume/content to electrical conductivity of the heart. Interestingly, this system responds relatively quickly to these demands, especially when starting from sctatch. More red blood cells are made and total blood volume increases, which allows the heart to supply blood to the entire body more easily. Until these adaptations are long underway, the rest of the body has to sit tight.
Weeks 4-8, should begin to feel very different to the novice runner. The cardiovascular system has started to make breathing a bit easier and effort feels more easy too. The neuromuscular system has made lots of adaptation now as well, which means that motor patterns are fired off more efficiently. Running begins to feel familiar, less awkward, and requires less brain power. If I had to guess, most novice runners in this period begin to experience rapid changes in the pliability of the soft tissue.
At this point in the training cycle, total weekly mileage is beginning to far exceed typical daily wear and tear on the body, and as Wolff's law suggest, collagen fibers in tendons and ligaments begin to respond to these stresses, demonstrating increased strength and elasticity. Likely, this would be the time that increases in bone density are beginning to peak as well. I would argue that many runners toward the end of week 8 are begging to feel invincible, strong, and very fit.
In weeks 8-11, I pay extra close attention to my runners: I may call this the 'danger zone' if I'm being dramatic. This is the period in which many novice runners will run their longest miles and clock some their highest weekly totals. I have some thoughts on why this period can be so provocative and injurious.
Theory #1: up until this point, running performance has been largely limited by cardiovascular fitness and subsequently by the neuromuscular system. At the 8 week mark, both of these systems are in fine-tuning stages, which means the body can function at a higher performance. I believe two things happen here.
First, the musculoskeletal system is now the greatest limiting factor. The highest stresses are being thrown onto the muscles and tendons: faster paces and longer distances. The unfortunate reality is that muscle development at this level adapts more slowly than the previous two systems. In spite of this, training load does not plateau, but instead continues to add stress to the system. Novice runners with focal or generalized weakness may begin to show early signs of injury here. If your nutrition isn't right, it will start to take its toll here as well.
Is this the best phase to begin to address strength deficits with novice runners and can it be protective against injury?
Theory #2: many novice runners will continue to transition to longer runs in this phase. As cardio fitness increases and runs get longer, runners are less likely to engage in quality speed workouts (depending on the training plan), and even if they are, the absence of heart-rate training means they may not reap the most benefits.
The continuance of quality, heart-rate-based speed work in the mid to late phases of training can be a powerful catalyst in the continued development of leg strength, triggering excretion of endogenous growth hormone from the brain. These two things are crucial for keeping the body strong and healthy during weeks of high mileage.
Growth hormone (GH) excretion rises exponentially with effort, peaking at around 90-95% of max HR. GH is critical in the development of bone density, tendon growth, and development of red blood cells. It is also a crucial factor in helping the body utilize fat as a fuel source, a necessity for long distance endurance events. Novice runners not privy to the best ways to approach speed work will either not benefit from these injury protective benefits or run the risk of injury from performing speed work too aggressively. When it comes to speed work, it's all about quality over quantity.
Can better executed speed workouts be protective against injury in later phases of long race training?
Theory #3: genetics largely dictates many of the parameters we try to manipulate with training. One of the biggest ones that is difficult to control is the genetic distribution for slow twitch and fast twitch muscle fibers. The prevalence of the body to shift from sugar burning to fat burning is largely affected by the duration of the activity. Although there is individual variation, most of us start out running on predominately sugar and by the time we reach 90 minutes of running, are close to 90% fat burning. For the genetically gifted, this transition will be seamless.
There is a select amount of muscle that is moderately adaptable with training in ability to become better at burning fat, but genetics will dictate the amount of endurance muscle fibers you have to work with. Runners who are genetically higher in fast twitch or glycolytic fibers will simply not perform as well as distances increase. These runners will likely need more time in this particular phase of training to optimize the benefits of long runs.
I would guess that these runners are more susceptible to injury during this phase as well, because it can be argued that runners with a higher natural proportion of endurance fibers would have been developing strength in those fibers throughout the previous 8 weeks of training. I'll remind the reader that most of the research in this area has been done on runners who are likely predisposed to long distance running in the first place. Be that as it may, it stands to argue that those suited for shorter distance running may require more time to adapt to longer distances, lest they run a higher risk for injury.
Is there a good way to identify runner who would benefit from a prolonged conditioning period with additional long runs?
Get more runners to the starting line
These are some thoughts I consider while on the run. I'm deeply invested in helping novice runners be successful, stick around, and be a part of the continued growth in popularity of this sport. I could go on for hours about the ways becoming a runner has benefited me, physical, mentally, and emotionally. If I could give one thing to all of my runners, it would be the ability to be a life-long participant in meaningful, physical activity.
Inevitably, I maintain the mindset of an ultra runner, which revolves around the idea of conditioning the body to sustain and tolerate high mileage running year 'round. This mindset centers around the optimization of every system from training to nutrition. I know this is neither practical nor in the interest in most novice runners; however, consider the implications of being able to adapt a training protocol in such a way that could provoke such a tolerance to activity in even the most mortal of novice runners. Wouldn't that by far improve the confidence in our trainers that runners can take part in these protocols with fewer injuries and fewer missed races?
Many of the typical training regimens in existence were developed to maximize performance for racing, even some of the more modest protocols. These programs are designed to maximize training efforts in a given amount of time to elicit a maximal stimulus in physiological changes to the body. What if there was an alternative that spread that time out and allowed novice runners to develop in a manner that emphasized life-long, injury free running? How would you work with these runner differently?
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Until next time, don't stop moving!