Upon completing his PhD, Blatherwick worked with the Auggies hockey team at
Augsburg University, testing them on strength, speed and endurance using methods that he had personally developed. After the Auggies won the
NAIA Ice Hockey Championship,
Herb Brooks asked Blatherwick to test the
members of the 1978–79 Minnesota Golden Gophers on the ice and in a laboratory setting. His methods for endurance included short under-five second bursts of flat-out speed, followed by a slowdown period to resemble periods during games. Blatherwick suggested to Brooks that he runs practise at faster speeds to better prepare players for game settings. His methods gained recognition from the
National Hockey League (NHL) and he worked part-time as a conditioning coach for the
Minnesota North Stars, earning the nickname Cardiac Jack because of his workouts and continuous use of the words 'cardiovascular fitness.' He later said Brooks would call him early in the morning to discuss on- and off-ice practice routines. Brooks' son Daniel later said: "I don't think the Miracle on Ice could have happened without Jack." While working with the Rangers, Blatherwick conditioned players "through such off-ice flexibility exercises as a series of two-legged and one-legged jumps wearing weighted vests and running in place on a portable jumping pit with quick high-knee lifts." From 1986 until 1991, Blatherwick worked a conditioning coach for the Gophers. He then spent one season as the head coach of Hopkins ice hockey team before joining Brooks as an assistant coach with the
New Jersey Devils in 1992. In 2005, Blatherwick established the Hockey Development Committee to "set the development structure for MYHA girls and boys teams from Termites through Jr. Gold within the guidelines and rules of District 6, MN Hockey and USA Hockey." In 2009, he was inducted into the Minnesota Hockey Coaches Association Hall of Fame. Blatherwick later joined the
Washington Capitals organization as their exercise physiologist, earning praise from strength and conditioning coach John Wawrzyniak. In 2019, Blatherwick was the recipient of the
Lester Patrick Trophy "for outstanding service to hockey in the United States." ==Selected publications==