critical for safely performing squats and other barbell-based free weight exercises. The Smith machine does have some advocates amongst experienced trainees, however. The "bar path" issue is minimized for exercises involving a short range of travel such as calf raises and shrugs. It is potentially good for performing exercise variations when progress has slowed using other exercise forms, although care must be taken to avoid joint stress issues. The removal of stabilizing muscles as a factor can also allow one to increase the intensity applied to primary muscles. 3D Smith machine A conventional Smith machine has one degree of freedom – the bar can move up and down in a straight line along a vertical track. (Rolling the bar is also typically used to activate the safety locks.) Some variant designs allow an additional degree of freedom – forward and back – while still keeping the bar from rotating or moving side to side. These machines are sometimes called "3D Smith machines" or "Jones Smith machines". A few designs, such as Shermworks' "Free Spotter" or TuffStuff's "XPT Training System", permit almost all degrees of freedom while still incorporating user-activated safety catches (as opposed to the passive, pre-set safeties of a power rack). Origin and history The Smith machine was invented by American Jack LaLanne, who rigged up a sliding apparatus in his gym in the 1950s. It was spotted by Rudy Smith, who commissioned Paul Martin to improve it. Smith then installed the modified model in a gym he was managing at the time, Vic Tanny's gym in Los Angeles. By the end of the 1950s, Rudy Smith was an executive in Tanny's chain of gyms, and the Smith machine was being manufactured and sold more widely. Effectiveness Research published in December 2009 reported that free weights triggered 43% more activation of the muscles than a Smith machine when performing squats. References Weight training equipment