Criticisms of the FMS
Published reviews of the FMS agree that the composite score can distinguish those at higher risks for injury.74,75 However, concerns about the tests validity, learning effect, cut point, and use as a measure of rehabilitation have been raised. The validity of the FMS is questioned by studies showing that test scores are not well correlated to each other,76 nor are they strongly related to measures of core stability73 or static balance.77 Sensitivity and specificity for the FMS are rather low. The reported sensitivity scores are .45, .54, and .58 with specificities of .71, .74, and .91.62,64,68 Frost et al78 points out participants can adjust their movement to better fit the scoring criteria and that changes to the composite score may be from a learning effect rather than from training or functional ability. While several studies do support the use of 14/21 as the cut point for injury risk, some have been critical of the fact that all 7 tests are weighted the same.75 And there are several studies that support higher65,79 or lower cut points.66 Next, functional training programs have not produced scores that are significantly different from traditional weight training programs.80,81 Lastly, the claim that higher FMS scores relate to better athletic performance has not been substantiated by any research study thus far.70,73
Dynamic Valgus Testing
Several authors have suggested that an athletes risk of ACL injury can be established by looking at knee position and lower leg alignment during jumping and squatting movements.82-84 Video analysis of non-contact ACL injuries revealed that the knee was often in a valgus position with the hip externally rotated.85 Further biomechanical analysis of male and female athletes has revealed a number of interesting things; females generally have less knee and hip flexion at landing,86 their knees and feet are closer together than males at take-off and landing,87 and in females one or both knees are more likely to pinch inward.86 Females reach maximal levels of hip adduction, knee flexion, and genu valgus earlier in the declaration phase (landing) than males88 and changes during puberty have been noted with males decreasing valgus alignments as they mature.89 As discussed in Chapter 8, women have a significantly greater risk of ACL injury than men, the gender differences seen in biomechanical analysis has lead a number of researchers to propose that a lack of neuromuscular control during jumping, cutting, and stopping maneuvers is a modifiable risk factor for ACL tears.82-84,87
Testing for dynamic valgus began with sophisticated video and force analysis equipment in biomechanics labs in the early 2000s, but has become more accessible to coaches and athletic trainers. Several studies have shown screenings using little to no video equipment to be sensitive and reliable.90,91 Munro points out there are several movement components that make up the position that is commonly referred to as dynamic knee valgus and the degree to which an athlete displays any of these differs. They include hip internal rotation, pelvic drop, hip adduction, tibial external rotation, and mid-foot pronation.82 Figure 10-4 is a classic example of dynamic knee valgus during landing.
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The severity of dynamic knee valgus can be measured as knee separation distance (KSD) and frontal plane projection angle (FPPA) when still video frames are used (Figures 10-5 and 10-6).
Other techniques include counting the number of alignment and balance errors seen, grading scales of mild, moderate and severe, or positive/negative determinations.
There are several jumping, cutting, and squatting movements in the literature that produce observable dynamic knee valgus in participants. The most commonly used one is the drop vertical
Another test developed by Padua et al uses a slightly different jump and is scored by counting the number of misalignments.92 The landing error scoring system or LESS can be done with or without video recording. The jump for LESS combines a forward motion (Table 10-6).
Instead of coming straight down from a 12-inch box, athletes are instructed to jump out to a distance equal to half their height, and then perform a maximal vertical jump. Higher error scores mean greater dynamic valgus and thus higher risk. If screening without video replay, the athlete should repeat the jump 4 times while the clinician looks for 10 possible errors.91 If video footage from the front and side are used, then there are 17 possible errors. Errors are weighted as 1 or 2 point mistakes, so that the maximum scores of the tests are 15 and 18, respectively.
A single leg squat will also induce knee valgus in many athletes (Figure 10-7). Ugalde and colleagues found that the single leg squat was equally as effect as 2-D video analysis of DVJ test in high school and middle school athletes.93 An additional advantage of the single leg squat according to Munro is that it puts the least amount of strain on the ACL and presents the lowest risk of injury.82