For anyone who has ever done continuous labor or a long-lasting workout, the sensation of heat or “burning” in your muscles is not a foreign concept. As a former rider with Biking for Babies, I could pretty much predict when I would start to feel the “burn” in my quads. It was generally when I was training at a higher level than I was previously training. For example, once a 60-mile ride became (more-or-less) comfortable and “easy,” I knew that once I increased that mileage to 70 miles, I was going to feel it. But, to prepare for the ride, that was what needed to happen if I was going to bike back to back to back to…you get the picture…100+ mile days.
For our riders, their muscles must get bigger and better as they train. There are two exercise physiology principles that govern how they do that: overload and specificity (Powers and Howel, Exercise Physiology. 6th edition). The principle of overload requires that muscles be exercised at a level beyond what they normally workout at. Basically, if I do 10 biceps curls with 15 pounds each day without increasing the weight or frequency, my muscles will stay the same. But if I increase the weight every week, my muscles will get bigger and stronger. The exercise also must be specific to the exercise goal. In the case of our missionaries who are cycling hundreds of miles, if they lift a lot of weight one time each week, and correctly increase that weight as they train, they may get stronger, but their endurance to do the ride will be less than satisfactory. 
What I have always loved about working with athletes and studying Kinesiology is the complete understanding that you have to take the physical body out of its “comfort zone” for it to change and get better. If that is how God designed our bodies, we should not be shocked that our spiritual life and souls are strengthened in a similar fashion.
In the first letter of Peter, Peter writes, “In this [salvation] you rejoice, although now for a little while you may have to suffer through various trials, so that the genuineness of your faith, more precious than gold that is perishable even though tested by fire, may prove to be for praise, glory, and honor at the revelation of Jesus Christ” (1 Peter 1:6-7). In this phrase, Peter is harkening back to several Old Testament passages using the purification of metal in fire as an analogy for the purification of the soul (Daniel 12:10, Zechariah 13:9). As our missionaries are training their bodies for the goal of completing the National Ride, they MUST train their souls if their final goal is to embrace all of the grace that Christ offers them.
Christ calls us into a relationship with Him, and that requires us to accept and carry out what He commands (John 15:13-16). But, just like exercise, we need to be open to God’s grace to push us out of our “comfort zone” so that we may grow to love Him more and be conformed to His image here on Earth.
I love seeing the physical transformation of our missionaries, but the more important goal of training and the ride is to allow Biking for Babies to be an avenue for our missionaries to be tested spiritually and to finish the ride more connected with Christ. I have watched God call young adults, from all walks of life, to let go of the comforts of this world they are clinging to so that they may cling more tightly to Him.
Although uniting ourselves with Christ is an expectation of the Christian life, it is still difficult. That is why it is important that we continue to pray for our missionaries, who are being tested in so many ways, so that their fruits may be of God and not of their own. Pray that they continually find themselves at the foot of the cross. Pray that they see how they can live each day as better witnesses to the Faith. Pray that they may undergo the test with endurance so they may increase in character, and ultimately increase in hope in the saving power of Christ (Romans 5:3-4).
