Editor's note: This article was originally published on Kevin A. Thompson's blog. It has been modified and republished here with permission.

CrossFit is a life-transforming exercise program.

The benefits of CrossFit are many, including increased:

• strength

• agility

• endurance

• confidence

I have seen the benefit to many friends and church members who begin CrossFit.

Yet CrossFit shares a hidden secret with many other formal workout programs.

Exercise can bring tremendous benefits to a marriage, yet on many occasions I have seen well-intended people start exercise programs and they end up making decisions that hurt their marriage.

As long as someone knows the risks and makes good choices in response to those risks, the benefits of exercise far outweigh the dangers. However, if someone blindly signs up and never considers what boundaries they need to set, a new exercise program can have fatal consequences.

Three Reasons Affairs Happen in Exercise Programs

1. Because some are looking

Some begin to exercise as preparation for the next relationship. Knowing their marriage is ending, they begin to workout to make themselves more attractive for what will come next. Since their present relationship is unhealthy and they are already considering the next step, it makes them very susceptible to an inappropriate relationship.

Others aren't just susceptible, they are on the prowl. Their pain is so great and their loneliness so deep that they are willing to connect with anyone no matter the personal cost to the other person. Maybe they are aware of their desire, many times they are not. Either way, knowing that some are looking for a relationship should cause a faithful husband or wife to be on their guard. It doesn't prevent them from joining the program; it simply gives them an awareness and wisdom in how to interact with others.

2. Because some are unaware

While some are looking for relationships, others are unaware of the danger.

Human willpower does not come in infinite quantities. It is limited. When we use discipline and willpower in one area, our resolve is depleted in another area. Much like a muscle reaches the point of exhaustion, so does willpower.

The good news is that willpower can be developed. By excercising willpower, it is strengthened. This is one reason exercise is a beneficial routine. The discipline creates more discipline.

However, when we start a new activity which requires willpower, we must be very aware of its effects. Using our willpower to workout puts us at risk for other bad habits.

Staying faithful to a relationship is a combination of building a healthy relationship, creating wise boundaries, and resisting temptation. When we are using our willpower in other areas, we must be cognizant of the danger and compensate for the threat.

3. Because the conditions are right

Even if a person isn't looking and they are aware of their diminished willpower, affairs can occur simply because exercise helps one's sex life.

Moving from a sedentary lifestyle to an active lifestyle makes one look, feel, and interact better.

Looking

better makes them both more attractive to others and more confident in themselves. This confidence easily translates to an openness to sex.

Feeling

better includes an increased production of testosterone which increases aggressiveness and sexual desire. A person will desire sex more and be more likely to initiate.

Interacting

better moves one from isolation to community. Whenever a couple asks for advice of how to reconnect, I often encourage them to start a new hobby together. Exercising is a great option. Doing an activity together can greatly bond a couple. This is a great gift to a struggling marriage, but it is a great threat when the man and woman aren't married to each other.

Looking, feeling, and interacting in better ways because of exercise can be a threat to marriage, but it can also be a great benefit. If these qualities are not used to engage in an inappropriate relationship but are used in relation to one's spouse, the results can be dramatic.

If you want to exercise, but do not want the program to hurt your marriage, adhere to the following guidelines.

Ten Guardrails for an Exercise Program

1. Check your intent before starting a program. Are your motives pure?

2. Develop a healthy relationship with your spouse.

3. Make a conscious decision to be a person of high character and integrity.

4. Have an accountability partner who asks you questions about your feelings toward people of the opposite sex.

5. If possible, workout with your spouse.

6. Do not exchange phone numbers with people of the opposite sex that you meet at the gym.

7. Do not engage in conversations with people of the opposite sex outside the gym. (i.e Facebook, Twitter, etc.)

8. Make sure you have transparency with your spouse regarding passwords and social media accounts.

9. Have a healthy skepticism about the intentions of others.

10. Go to workout; get your emotional needs met in other places.

Endnote: Some might roll their eyes at this post thinking it is foolish. It's OK to disagree, but just remember that I regularly sit with couples within hours after an affair has been revealed. I can't tell you how often I have heard, "I met him/her at the gym. It started innocently, but "¦"