1. Improved Drop Landing Kinematics and Resistance to Fatigue
Following Participation in Two Neuromuscular Training Programs
Nathan J. Robey1, Luzita l. Vela2, Joni A. Mettler3, Rod A. Harter3, FACSM 1Sport and Exercise Science, College of Natural and Healthy Sciences, University of Northern Colorado; 2Kinesiology, College of Nursing and Health Innovation, University of Texas - Arlington; 3 Biomechanics/Sports Medicine Laboratory, Texas State University, San Marcos, Texas
Background and Significance
ACL injuries in active populations result in an estimated $1-3 billion in associated medical costs, creating a significant burden on the health care system [1]
A majority of the ACL ruptures are the result of a non-contact injury mechanism
Females are reported to be at a 3-5 times greater risk of ACL injury than male counterparts [2]
Reduced knee flexion, knee valgus collapse, and increased tibia internal/external rotation has been suggested as a possible ACL injury risk factor [3,4]
Hip abduction weakness and acute fatigue are thought to negatively influence the amount of dynamic knee valgus [5]
The Landing Error Scoring System (LESS) is a low- tech drop landing field test that may be used to screen athletes for ACL injury risk [6]
Prevention programs have demonstrated the ability to reduce ACL injury rates; however, ACL injury prevalence remains, especially in female athletes [4]
Lower extremity neuromuscular training has been suggested as a method of reducing ACL injury rates
Methods and Materials
The NMT Programs were each performed 4 days per week for 4 weeks.
Isolated fatigue protocol was induced using a standing hip abductor protocol modified from Thomas et al [7] that employed an isokinetic dynamometer.
Pre-fatigue and post-fatigue measurements were taken at Week 0 and Week 4:
Neuromuscular Training Programs
Results
27 of 32 participants (84%) recorded perfect attendance to supervised training session indicating high compliance to NMT protocols.
Concentric hip abduction peak torque increased in both the Plyometric (27.9%) and Traditional exercise (19.9%) groups after 4 weeks (p < 0.001).
No significant differences between groups were observed for these measures (p > 0.05).
Closed kinetic chain leg press peak force improved in both the Plyometric (12.4%) and the Traditional (21.3%) groups from Week 0 to Week 4.
3-way Mixed Effects ANOVA revealed significant differences on the LESS test for Group (p < 0.05), and Time and Fatigue Condition interaction (p < 0.001).
At entry into the study, the mean post-fatigue LESS scores were 9.06±1.49 for the Plyometric group and 6.89±1.69 for the Traditional group (p > 0.05).
Plyometric NMT group improved LESS scores at Week 4 in both pre-fatigue (16.7%) and post-fatigue (11.6%) drop landings when compared to Week 0.
Traditional NMT group improved LESS scores at Week 4 in both pre-fatigue (9.0%) and post-fatigue (7.9%) drop landings when compared to Week 0.
Traditional Exercise
Sets x Repetitions
Standing hip abduction with Thera-Band®
3 x 15
Standing hip abduction with 45° with Thera-Band®
Monster walks with Thera-Band®
Clam shells with Thera-Band®
Single-legged bridges
Single-legged deadlifts
Single-legged squats
Figure 1. Isokinetic dynamometer testing positions (below): Hip abductor peak torque (A) and closed chain leg press peak force (B). A B
Table 1. Traditional Exercise Group Protocol. Participants were progressed to next stiffest resistance band at mid-point (2-week) of the study. Red color band was initiated at the start of the training program and the progressed to the green color resistance band at the mid-point of the study. B
Plyometric Exercise
Sets x Repetitions
Forward/backward single-legged line jumps
1 x 30
Side-to-side single-legged line jumps
High skips
1 x meters
Distance skips
Broad jumps
2 x 10
Tuck jumps
Alternating single-legged lateral jumps
Purpose of the Study
To compare the effects of participation in two different week lower extremity neuromuscular training (NMT) programs (Traditional versus Plyometric) on acute hip abductor muscular fatigue and LESS scores in physically- active women.
Participant Demographics
32 physically-active women (age = yrs; height = m; weight = kg) were randomized to one of two 4-week neuromuscular training (NMT) programs: Plyometrics (N = 15) or Traditional (N = 17).
Experimental Design
Single-blind randomized clinical trial
Three-way mixed effects ANOVA (a = 0.05)
Independent Variables:
Group (2): Plyometrics group and Traditional group
Time (2): Week 0 and Week 4
Fatigue Condition (2): Pre-Fatigue and Post-Fatigue
Key Outcome Measures:
Hip abductor peak torque at 120o/sec
Closed chain leg press peak force at 60o/sec
LESS test score (Jump landing assessment using 2 cameras and the original 17-point scale)
Conclusions
Both of the 4-week lower extremity NMT programs were successful in significantly improving hip abductor and leg press strength.
Perhaps more importantly, the Plyometric protocol produced significantly greater improvements in LESS test scores (both non-fatigue and fatigue states) than the Traditional program, possibly further reducing ACL injury risk in this population.
Table 2a. Plyometrics Exercise Group Protocol. During Phase 1
(Week 1 and Week 2), the participants engaged in the seven plyometric
exercises listed above.
Plyometric Exercise
Sets x Repetitions
Forward single-leg hop, hop, hop, and stick
1 x 10
Squat jumps
2 x 10
Single-legged maximal vertical jump
Single-legged jump for distance
Broad jump, jump, jump, vertical jump
1 x 5
180° jumps
Single-legged lateral jumps 1 2
References
1Frank BS, et al. Neuromuscular fatigue alters postural control and sagittal plane hip biomechanics in active females with anterior cruciate ligament reconstruction. Sports Health. 2014;6(4):
2Patrek MF, et al. Hip-abductor fatigue and single-leg landing mechanics in women athletes. J Athl Train. 2011;46(1):
3Hewett TE et al. Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes. Am J Sports Med. 2005;33(4):
4Noyes FR et al. Neuromuscular retraining intervention programs: do they reduce noncontact anterior cruciate ligament injury rates in adolescent female athletes? J Arthroscopic Related Surg. 2014; 30(2):
Geiser CF et al. Effects of isolated hip abductor fatigue on frontal plane knee mechanics. Med Sci Sports Exerc. 2010;42(3):
6Padua DS, et al. The landing error scoring system is a valid and reliable clinical assessment of jump-landing biomechanics: the JUMP-ACL study. Am J Sports Med. 2009;37(10):
7Thomas AC, McLean SG, Palmieri-Smith RM. Quadriceps and hamstrings fatigue alters hip and knee mechanics. J Appl Biomech. 2010;26(2): 3
Table 2b. Plyometrics Exercise Group Protocol. During Phase 2
(Week 3 and Week 4) the participants assigned to this group progressed to
perform in the seven plyometric exercises listed above.
Figure 2. The Landing Error Scoring System (LESS) test: (1) Preparatory phase; (2) Landing phase; (3) Jump phase.
Supported by grants from the Thera-Band Academy
and Texas State University’s College of Education
Presented at the 2017 Annual Meeting of the American College of Sports Medicine in Denver, Colorado