Fitness and Dynamic Movement Testing
Its common for coaches at all levels to test the fitness components of their athletes prior to the season. The testing serves multiple purposes; to determine a starting point for conditioning programs, assess the effectiveness of off season training, motivate athletes to be compliant with a conditioning program, and possibly predict which athletes will perform well. It has also been assumed that higher levels of fitness decrease ones risk of injury; however, evidence of this is limited. The following section will review widely-used fitness and dynamic movement tests and describe the research supporting or not supporting their use.
Maximal oxygen uptake (VO2max) is the gold standard for measuring cardiorespiratory fitness (CRF). This type of testing requires an athlete to run or bike at increasing intensities until they reach their absolute maximal heart rate and VO2, which are monitored throughout the test. While very accurate, max testing is expensive and difficult to do with teams. Instead, field tests have been developed that can estimate an athletes VO2max from a timed distance of running or level reached. Table 10-4 outlines several of the most frequently used CRF tests.
Tests that require continuous work for at least 8 minutes are considered aerobic. More intense protocols that require sprints are anaerobic. Sports that blend both aerobic and anaerobic metabolic systems such as soccer, basketball, lacrosse, and hockey will either use multiple types of CRF tests or a test that combines both continuous running and sprinting, such as the YoYo test.
Several recent prospective studies have examined the impact of aerobic and anaerobic fitness on injury incidence.45-49 The different measures used to assess CRF make conclusions about the predictive ability of a test difficult. Aerobic testing may be less useful than anaerobic tests in athletes, but more beneficial in military settings. Poor performance on anaerobic tests such as the 6 minute run and shuttle run increased the risk of injury46 and the time lost47 in rugby and Australian-rules football players. The evidence for traditional sports athletes is limited. Frisch et al45 reported that the shuttle run was not related to the incidence of injury in youth football players. A study of European male soccer players found that poor aerobic conditioning was a risk factor for severe injuries50 but a study of similar female athletes found no differences
Tests that measure neuromuscular elements such as strength, endurance, flexibility, or balance are frequently included in fitness assessments. Muscular strength, endurance, and flexibility are properties that are specific to a muscle or group of muscles that produce a specific movement. Strength is the ability to move a heavy load a limited number of times. Strength tests such as the one repetition max bench press or squat assess the athletes ability to recruit muscle fibers and maximal force production. Muscular endurance is the ability to contract a muscle over and over and tests the muscles capacity for work and energy production. Exercises like pull ups, push-ups, or curl ups done to failure are used. Muscle fiber type and history of training will dictate how strong or fatigue resistant a muscle is. Athletes can train to develop both strength and endurance within the same muscles. Muscle flexibility refers to the length of the muscle itself which can be increased with consistent stretching. Muscle shortness is one reason for limited joint ROM. Flexibility is measured as joint ROM. Tests such as the sit and reach and back scratch involve multiple joints. Individual joints can be assessed by goniometry. Balance tests assess the coordination of the muscle actions, kinesthetic awareness, and nerve conduction.53 Balance can be measured in both static and dynamic conditions. Holding the body stable while standing on one foot is an example of static balance. Maintaining proper alignment while bending forward and lifting the non-stance leg is dynamic balance. The term dynamic stability is also used to note a larger contribution of core and trunk muscles needed to perform more challenging movements.
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There are numerous tests to assess the muscular strength, endurance, dynamic stability, or flexibility of athletes. Again because so many different tests are used, it is challenging to determine which if any, can be used to predict injury risk. Test results for one muscle group should not be generalized to the whole body. For example, the push up test assesses the muscular endurance of the pectoral and triceps muscles and an athlete may score very poorly on it but very high on maximum repetitions of the leg press. Multiple tests should be conducted if whole body results are desired or coaches may focus on muscular groups and movements that are key to their sport. There is little evidence that general muscular fitness tests are predictive of future injury (Table 10-5).
Some specific measures, uncommon to pre-season assessments, are more sensitive for certain of sport-related injuries. Reviews by Dallinga et al54 and Murphy et al55 suggested that tests of dynamic stability, hamstring to quadriceps ratio, ROM, and muscular imbalance at the ankle were clinically useful screenings. The Star Excursion Balance Test (SEBT) may be a particularly good tool for female athletes. Plisky et al56 found that asymmetries on the anterior reach greater than 4 cm increased the risk of lower extremity injury nearly 3 times. Females with composite reaches < 94% of their limb length had 6.5 times the risk of injury as those with better reach scores.56 Balance and postural sway tests may also be predictive of future ankle injuries. The simple Single Leg Balance (SLB) test was used by Trojian and colleagues57 to screen high school and college athletes for ankle injury risk. The RR for ankle sprain was 2.54 (95% CI, 1.02 to 6.03) if the SLT was positive.57 Leetun et al58 took isometric strength measurements of several trunk muscle groups including hip adductors, abductors, and internal and external rotators in college basketball and track athletes. Only poor hip external rotation was a significant predictor of lower extremity injury. A laboratory study of trunk stability found an increased likelihood of knee injury (OR = 2.14, p = .009) if athletes were unable to resist lateral displacement.59 Muscular imbalance between the hamstrings and the quadriceps can be measured as a ratio between the 2, known as the H:Q ratio. This test requires an isokinetic dynamometer that is not widely available to most clinicians. Lower ratios indicate quadriceps dominance over the hamstring muscles and has been predictive of ACL injuries in women60 and in hamstring strains in football.61 An imbalance of strength or flexibility of the ankle increased the risk of ankle sprains in college-age athletes.60 Ankle ROM is easily measured with a goniometer yet strength tests are best done with isokinetic equipment. Of the tests reviewed only the SEBT, SLT, and ROM measures are clinically relevant. Because of the lack of field tests to predict injury, clinicians have either developed their own testing programs or adapted laboratory measures. Two examples are the Functional Movement Screen (FMS) (Functional Movement Systems Incorporated) which combines dynamic stability and flexibility and tests of dynamic knee valgus for ACL risk.