Training Study 001 - strength & endurance
Every now and then I get pulled into a rabbit hole on training studies, trying to understand how our bodies perform and what training factors can be manipulated to move the needle of athletic performance. This one in particular looks at endurance-trained runners and cyclists and the effect of adding heavy or explosive strength training on their endurance performance. Published by B. R. Ronnestad and I. Mujika in 2013, this review took a bunch of studies and brought all the info together into one updated synopsis!
It’s common knowledge that strength training is a beneficial component for an athlete’s overall performance and development. Strength training prevents injury and builds stronger muscles which in theory leads to a faster, more durable athlete. But beyond the surface level, what are the actual mechanisms of how strength training directly translates to endurance improvements?
Let’s Dig In!
The article focuses specifically on two types of strength training: heavy strength training vs explosive strength training. Explosive strength training is defined as exercises maximizing the concentric (muscle shortening) phase with a load ranging from 0-60% 1RM (Rep Max). Heavy strength training is defined as training to increase or maintain muscle, generating max force, and a load ranging from 1RM to 15RM.
Next, what qualities does an endurance event entail? Endurance competitions are primarily determined by the max power production an athlete can sustain for a given distance and the energy cost of maintaining that speed. Shorter distance races would go further to include the ability to accelerate, anaerobic capacity, and max speed.
Factors (discussed) Influencing Endurance Performance:
Exercise Economy
Exercise economy is a measure of how much oxygen is consumed per unit of work performed (watts or kcal/min). Higher exercise economy means performing at a higher speed/intensity with less effort, or sustaining a constant speed for longer duration.
2. Lactate Threshold
When exercising, lactate along with hydrogen ions are produced and released into the bloodstream. Lactate is actually just a fuel source that also aids in buffering hydrogen ions. Those hydrogen ions are the real villain when talking about “lactic acid”. As intensity increases and you reach LT - hydrogen ions build up faster than the body can remove them, creating that muscle burn - i.e. fatigue. Improving LT again would mean holding a higher velocity/power output during prolonged exercise.
3. Running Speed and Power Output
Power output is how much “work” (force * distance) the athlete can produce over a period of time. Anaerobic capacity is the body’s ability to produce a short burst of energy without use of oxygen - i.e. sprints! Both anaerobic capacity and peak power output can get an athlete into a good position at the start of a race, close a gap, break a pack, or win on the final kick!
Brief Findings:
Of all the studies reviewed, there were clear results that strength training improved exercise economy substantially in endurance runners. Whether the training format was heavy or explosive - just 6-12wks of added strength training improved running economy (Paavolainen et al., 1999). Results on cyclists were more mixed; this could be for many reasons - study protocols, cycling using different leg movement, etc. However, there was a notable study finding superior economy improvement after a period of heavy strength training - where the cyclist did a 3hr submax ride with 5min threshold periods every 30mins (Ronnestad et al., 2011).
Lactate threshold is primarily determined by VO2max and exercise economy. There were no direct studies saying strength training improved LT. However, since strength training improves exercise economy, it’s reasonable to expect the athlete to then be able to hold a faster speed at their lactate threshold.
Running speed and power output are also influenced by VO2max and exercise economy, but involve anaerobic capacity and neuromuscular attributes. Heavy strength training increases muscle cross-sectional area, directly leading to an increase in power output (Izquierdo et al., 2004). MRI imaging showed increasing max strength reduced the amount of activated muscle to generate the same power (Ploutz et al., 1994). Meaning the muscle strains less to put out the same amount of work.
Okay, so we’ve learned that strength training improves exercise economy, and that in turn can improve performance at LT, and having stronger muscles will allow me to produce more power and improve my max speed… but HOW?
Nitty Gritty - Potential Mechanisms:
Altered Muscle Fiber Type Recruitment Pattern
Increasing max strength of your Type I (slow twitch) muscle fibers delays activation of less efficient Type II (fast twitch) fibers. Type I fibers are the primary fibers being used in steady state exercise below LT - you want them to last as long as possible because Type II fibers were made for speed and get tired quick!
2. Increased Proportion of Type IIA Fibers and Reduced Type IIX Fibers
There is potential to shift the type of fast twitch muscle fibers utilized. Type IIA fibers have a high power output capability and are more fatigue-resistant than Type IIX. Shifting your muscles from automatically recruiting Type IIX fibers to IIA could allow you to hold a high output for slightly longer.
3. Increased Max Force and Rate of Force Development (RFD)
RFD is how fast you can generate force over a given period of time and is directly linked to improving neural activation or signal speed from the brain to the muscles.
Faster RFD means shorter contraction time with high force production. With a faster muscle contraction, you shorten the period of blood restriction within that muscle. Allowing more blood flow through the muscles, lowering the relative exercise intensity!
4. Increased Stiffness of Lower Body Muscle-Tendon System
Strength training of both types can increase the stiffness of the lower body tendons, specifically the achilles tendon. The stiffer the tendon - the faster the transfer of force.
With each foot strike as you run, your tendons are storing and returning elastic energy. This is known as a Stretch Shortening Cycle. Think about a coiled spring, or how some runners appear to be bouncing on their toes with each step.
For cyclists this differs because they are not able to store energy during the eccentric (muscle lengthening phase) and translate it into the concentric phase. The primary movement of cycling is all concentric muscle action.
Out of the Lab and into Training!
So how can you apply this to your current training regimen?
If you are a trained endurance runner - you will get the most benefit from 2 strength sessions per week. There are multiple ways of going about it. You could periodize phases of heavier strength training blocks into explosive strength training blocks, or simply have one “heavier” day and one explosive day. Either way, studies show you will see improvement if training within the right parameters (i.e. intensity and speed). Once you enter the competitive season, you can drop to one explosive strength session per week using high intensity and low volume. Remember with explosive training you want to focus on driving the weight up as fast as you can, whereas heavy strength training will need to be much slower with a focus on proper form.
For cycling most benefit was found through heavy lower body strength training. It’s important to note that whether you use the heavy strength model or explosive - the primary target for this is the lower body. That isn’t to say other muscle groups don’t need to be trained, but when talking about power production and speed within running/cycling we are referring to the legs!
Acknowledging the fear of hypertrophy/muscle mass for endurance athletes:
As a strength coach in the NCAA and an endurance athlete myself, one of those most common hesitations I see with athletes and strength training is the fear of putting on muscle mass. To be fair, we live in the age of comparison and with the amount of junk the internet serves - I don’t blame them. To put that fear away, there is a deeper understanding of the cellular signaling involved with both strength training and endurance training you need. As a coach, it’s always my goal to educate athletes and get them to trust that strength training will only benefit them.
Here is a last bit of science:
When you strength train, you can induce a hypertrophic response. This is a signal for the body to begin building new muscle via a process called muscle protein synthesis. But when you are endurance training, your body is sending opposing signals, impairing that hypertrophic response.
Several studies found that 8-16wks of strength training failed to increase total body mass and did not compromise VO2max in endurance athletes. There can be a small amount of muscle hypertrophy (3-6%) within the target muscles, however generally there is no natural occurring hypertrophy seen with strength training and endurance athletes (Ronnestad et al., 2010a).
Remember, the primary explanation for improved endurance performance is adaptations within the trained or new muscle! Postponed activation of less efficient Type II fibers, improved neuromuscular efficiency, conversion of fast twitch Type IIX into higher fatigue-resistant Type IIA fibers, and improved musculotendon stiffness - are all microscopic changes to the muscle that only specific strength training can induce.
Most importantly, all studies in the review found NO NEGATIVE EFFECTS of strength training on endurance performance. Whether you are new to strength training or have trained for decades - training intentionally to actually increase max strength or power can be what helps you get to your next breakthrough.
