Strength and core are pivotal for any cyclist. Yes, your huge legs are like pistons that shove power to the pedals moving you forward but a piston without an engine block has no power. Your core is what your legs push off of to create the power at the pedals. In cyclocross poor core strength is harder to fake than on the road.
Force production from a cyclocross race is much more taxing than on the road. Have you ever wondered why your back hurts at the end of a cross race but you have had 3 bike fits in the last year? As you produce high force pedal strokes coming out of corners, up steep hills, through mud and grass your core fatigues causing it, and your back, to hurt.
logan VB regional cx strength article
In the file above from 1 lap of a cyclocross race we can compare wattage to RPM. Unlike road racing or even Mountain biking, Some of the highest power spikes such as between the time of 1:18 and 1:19 the power spike starts at below 50 RPM. At such a low revolution per minute to create that wattage calls for much more force on the pedals. That high force high torque stroke causes higher muscle fatigue and higher stress on peripheral muscles and your core.
Cyclocross produces a higher fatigue load even from a muscle contraction standpoint. According to Henneman’s size principle, for a given muscle contraction your motor unit recruitment starts with slow twitch fibers and recruits more and more motor units moving into fast twitch fibers until the force your brain is calling for has been reached.  To produce more force your body can’t make the muscles contract harder you just recruit more muscle fibers to produce the desired force signaled by your brain. In cross you have more maximum muscle contractions than in any other form of cycling automatically calling for huge force production from all motor units to sprint up a steep climb or out of a turn. To increase your ability to produce this force you must do strength and core training.
Training peaks
Looking at this cyclocross race from a different perspective of the same one lap, you can see that each one second data point as a dot on this graph. The X axis is RPM and Y axis is Power. Looking at each dot above 500 watts a majority of these dots are between 50 and 90 RPM.  As the rider gets fatigued he has trouble producing the force to create the power over and over. Strength training and core strength can not only raise the max power spikes but also stave off fatigue so that the rider can produce the same power to the end of the race.
According to the study “Cyclists’ improvement of pedaling efficacy and performance after heavy strength training” cyclists that perform strength training in the weight room in concurrence with endurance riding can see a 5% jump in efficiency mostly from the “up” stroke created by core and hip flexor strength. In the study the test subjects “crank torque” was increased, that’s just what the doctor ordered for faster accelerations in a cross course. Better force and better torque out of turns and up steep climbs is what makes or breaks a cross racer in competition.
A way that we as coaches can see this data in action is with WKO4 and Pioneer or Quarq power meters that show left right pedal force differentiation. With some of the new features of WKO4 we can actually see how much force the leg on the opposite end of your pedal stroke is “sucking” out of the leg that is producing the power. The goal being that the leg in the power stroke is not hindered from the leg not producing the power.
We do a ton of “continued education” at Source Endurance to try and keep up to date with the latest studies, I’ll quote one more so you dont get bored to death with this article but some results from “Maximal Strength Training Improves Cycling Economy in Competitive Cyclists” showed improvements in aerobic and anaerobic power in cyclists that incorporated a weight lifting protocol into their training over the control group that continued to train without a weight or plyometrics workout in their training.
With results in studies this significant its a no brainier that depending on the time of year and your periodization as an athlete you should incorporate some gym time or plyometrics or both. What we recommend, and what is just now starting for Cross season specifically at the Source Endurance Training Center of the Rockies,  is a periodized plan for working in weights and plyo. If you decide to start lifting you can’t just jump into a squat rack and go for 3 sets of 5 squats at whatever you can lift, you will get injured. Talk to your coach, or read some literature on weight lifting. Just like endurance training you have to build your workouts into build cycles and rest. Start light with full body exercises and slowly put up higher weight over weeks and months of lifting cycles. Start with lifts that incorporate large muscle groups such as squats, lunges, and dead lifts. Plyometrics are also one of the best workouts with very specific movements to that of cross running and jumping barriers.

logan full stride

Cyclocross, cross training, training peaks, zack allison, cycling, coaching, strength, Core

Logan Vonbokel flew up the run up at Nationals in Austin Texas. Here you can see how specific a simple lunge or lunge jump can be compared to the motion in run ups.
Have fun! find a good group to workout with and don’t over do the lifting, you will definitely be sore the first time.