Simply defined, muscular Christianity is masculine, or "manly" Christianity. Throughout the nineteenth and twentieth centuries, Christian men in the United States have responded to the so-called "feminization" of American religion. From the seventeenth century through the end of the Victorian era, women comprised approximately two-thirds of America's Christian churches, and beginning in the 1850s men began to challenge women's dominance by making religion a manly endeavor. Organizations such as the Young Men's Christian Association (YMCA), Men and Religion Forward Movement, Boy Scouts, Christian Service Brigade, and, most recently, Promise Keepers sprang from this movement. These groups emphasize a uniquely masculine expression of Christian faith, American nationalism, citizenship, chivalrous behavior, and in some cases even skills in outdoor activities. Today, people often use the term "muscular Christianity" to refer to any type of male-dominated, outdoor, virile, or sports-oriented activity with a specifically Christian or evangelistic purpose.

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