• Cardiovascular system. Blood vessels in the active muscles and in the skin dilate, and the heart rate increases. These adjustments accelerate oxygen delivery and carbon dioxide removal at the muscle and bring heat to the skin for radiation into the environment.
• Respiratory system. The respiratory rate and depth of respiration increase. Air moves into and out of the lungs more quickly, keeping pace with the increased rate of blood flow through the lungs.
• Integumentary system. Blood vessels dilate, and sweat gland secretion increases. This combination helps promote evaporation at the skin surface and removes the excess heat generated by muscular activity.
• Nervous and endocrine systems. The responses of other systems are directed by controlling the heart rate, respiratory rate, and sweat gland activity.

Even when the body is at rest, the muscular system has extensive interactions with other systems. Figure 10-20 summarizes the range of interactions between the muscular system and other vital systems.

 Why would a sprinter experience muscle fatigue before a marathon runner would?

 Which activity would be more likely to create an oxygen debt: swimming laps or lifting weights?

 Which type of muscle fibers would you expect to predominate in the large leg muscles of someone who excels at endurance activities, such as cycling or long-distance running?