Crossfit is a method of training that proscribes random exercises with the goal of increasing strength, conditioning, agility, endurance, and many other physical skills. There is no exercise that makes Crossfit unique, but rather the method in which they are performed. There is no format in which the exercises are performed, so concepts like periodization are completely ignored. Consult your physician before starting any exercise program.
High Repetition Olympic Lifting
This occurs often in the Crossfit system, and is completely at odds with conventional programming. While doing 30 repetitions of the snatch as quickly as possible is an incredible conditioning workout, in actual Olympic style weightlifting, the reps are kept low to reduce the risk of injury. When performing an extremely skilled movement, and the snatch, clean and jerk are the most skilled lifts there are, care must be taken to avoid injury. Weightlifting has a lower injury rate than badminton. Crossfit seems to generate a record number of SLAP tears, or injury to the shoulder joint, or labrum.
Kipping Pull Up
This is another exercise variation fairly unique to Crossfit. While most programs call for strict form when performing chin-ups, a great deal of momentum, kicking, and bouncing out of the bottom called "kipping" is used to execute as many chins as possible in as little time as possible. Again, this is a lot of strain on the joint, including the bicep tendon, and may be another contributor to the high rate of SLAP tears experienced by Crossfit trainees.
Twenty Percent Slop
This is something that is condoned by Crossfit headquarters. The ‘slop’ ideal is often cited within the CrossFit community as 20 percent form degradation, which allows for a great deal of latitude with respect to performing exercises. This completely overlooks the fact that your training should support your goals, and if you are hurt, you cannot train effectively. One of the primary concerns of coaching is keeping your athletes healthy. Sloppy work does not do this.
There is little programming in Crossfit, so be wary if you are called on to execute a one repetition maximum. Contrary to the claims of Crossfit founder Greg Glassman, your resting heart rate has no bearing on your ability to pull a limit deadlift, and despite his claims, no one the history of Crossfit has pulled a 750 lbs. deadlift using Crossfit methods. Limit strength requires conditioning of the central nervous system, including improvements in inter- and intra-motor coordination as well as motor unit recruitment that do not occur unless they are trained regularly, and regularity is nothing that occurs in Crossfit.