The Effect of Eccentric Hamstring Strength Training on Muscle Function

The high prevalence of hamstring strain injury in sports, coupled with detrimental performance and financial effects of hamstring injuries, stress the necessity to implement an intervention capable of minimizing hamstring injuries for athletes. Nordic Hamstring eccentric strength training has shown itself to be an effective method of preventing hamstring injury. Eccentric strength training has also been shown to alter muscle architecture, joint stiffness, improve strength, and enhance dynamic performance, specifically vertical jump height. While there is limited research investigating the adaptations of the hamstrings to Nordic Hamstring training, determining these adaptations would allow for a better understanding of how the body responds to this injury-preventing stimulus. The purpose of this study was to examine the effects of Nordic Hamstring eccentric strength training on hamstring muscle architecture, stiffness, strength, and dynamic performance. We hypothesized that Nordic Hamstring eccentric strength training will increase hamstring fascicle lengths and cross-sectional area, properties of muscle stiffness as measured by shear modulus and passive knee flexor torque, maximum torque and angle of max peak torque, and vertical jump height.  A total of 17 recreationally active, adult participants between the age of 18 and 21 were randomly assigned to control or experimental groups. Control subjects (n=7) performed a warm-up and static stretching for 6 weeks while experimental subjects (n=10) performed a warm-up, static stretching, and progressive Nordic Hamstring strength training for 6 weeks. Pre- and post-intervention measurements included: muscle architecture and stiffness of the biceps femoris long head using ultrasound imaging, maximal isokinetic and isometric hamstring strength measured on a dynamometer, and vertical jump height performance. Muscle volume and physiological cross-sectional area (PSCA) were calculated from the ultrasound measurements. Within and between groups two-way repeated measures ANOVAs were used to determine significant interactions and main effects with an alpha level of p<0.05.  The experimental group increased volume in both hamstring muscles (biceps femoris 11%, semitendinosus 20%), with a 12% increase in PCSA for the biceps femoris long head muscle but not the semitendinosus (p<0.05). There were no changes to fascicle length, pennation angle, or stiffness that were unique to the experimental group. The 6-week intervention did not produce any significant group by time interactions for concentric, isometric, eccentric strength measurements or peak passive torque measurements. Vertical jump height was also not affected by the intervention. Overall, the 6-week Nordic Hamstring training intervention was a good training method for muscle growth and this adaptation in architecture translated to changes in eccentric hamstring muscle strength, although these changes did not reach statistical significance largely due to the dichotomy of responses in our training group. A sub-group analysis of the experimental subjects revealed apparent "responders" and "non-responders" to the training stimulus. From a clinically-relevant standpoint, the Nordic Hamstring training was 70% effective at improving muscle function for participants in this study. Future exploration of the mechanics behind the Nordic Hamstring strength training exercise, shown to reduce hamstring injury, is a necessary step in understanding muscular adaptations to resistance exercise and enhancing training effectiveness on hamstring muscle function.  M.S

Asymmetrical Landing Forces Detect Neuromuscular Fatigue

Neuromuscular fatigue decreases performance and increases injury risk, but practitioners lack an easy, reliable method for detecting fatigue. This study determined if ground reaction forces are impacted by neuromuscular fatigue and whether this differed between limbs. Thirty-one female athletes (19.1 ± 1.22 years, 1.7 ± 0.6 m and 63.0 ± 7.7 kg) participated. Each participant had vertical ground reaction force (vGRF) recorded during five trials of a forward jump task immediately prior to and following a competitive soccer season. During each trial, peak vGRF during landing for both dominant and non-dominant limbs and asymmetry of peak vGRF between limbs were calculated. These measures were submitted to a RM ANOVA to test the main effect and interaction between time (pre vs. post) and fatigue (starter vs. non-starter). A significant two-way interaction for dominant limb peak vGRF (p=0.034) was observed. Starters increased peak vGRF (p=0.049) at post compared to pre time point, but no difference was evident for non-starters (p=0.333). Asymmetry of vGRF (p=0.033) between limbs decreased at the post-season time point, but asymmetry did not differ between starters and non-starters (p=0.360). Ground reaction force data may be an easy, reliable for detecting neuromuscular fatigue

Sex and Limb Impact Biomechanics Associated with Risk of Injury During Drop Landing with Body Borne Load

Increasing lower limb flexion may reduce risk of musculoskeletal injury for military personnel during landing. This study compared lower limb biomechanics between sexes and limbs when using normal and greater lower limb flexion to land with body borne load. Thirty-three participants (21 male, 12 female, age: 21.6±2.5 years, height: 1.7±0.1 m, weight: 74.5±9.0 kg) performed normal and flexed lower limb landings with four body borne loads: 20, 25, 30 and 35 kg. Hip and knee biomechanics, peak vertical ground reaction force (GRF), and the magnitude and direction of the GRF vector in frontal plane were submitted to two separate repeated measures ANOVAs to test the main and interaction effects of sex, load, and landing, as well as limb, load, and landing. Participants increased GRFs (between 5 and 10%) and hip and knee flexion moments when landing with body borne load, but decreased vertical GRF 19% and hip adduction and knee abduction joint range of motion and moments during the flexed landings. Both females and the non-dominant limb presented greater risk of musculoskeletal injury during landing. Females exhibited larger GRFs, increased hip adduction range of motion, and greater knee abduction moments compared to males. Whereas, the non-dominant limb increased knee abduction moments and exhibited a more laterally-directed frontal plane GRF vector compared to the dominant limb during the loaded landings. Yet, increasing lower limb flexion during landing does not appear to produce similar reductions in lower limb biomechanics related to injury risk for both females and the non-dominant limb during landing

Sex Impacts Leg Stiffness When Increasing Stride Length to Run with Body Borne Load

Military personnel routinely run at a fixed cadence with body borne load, which may increase leg stiffness and potential injury risk - particularly for females. Seventeen males and ten females had leg stiffness quantified when running with four loads (20, 25, 30, and 35 kg) and three stride lengths (preferred, and ±15% of preferred). Participants increased leg stiffness (P=0.006), and potentially injury risk when running with load. But, a sex dimorphism in stiffness was evident with changes in stride length. Males exhibited reduced leg stiffness with longer strides (P\u3e0.05)

Sex Impact on Knee and Ankle Muscle Extensor Forces During Loaded Running

Background: This study determined whether the knee and ankle muscle extensor forces increase when running with a body-borne load and whether these forces differ between the sexes. Methods: Thirty-six (twenty male and sixteen female) adults had the knee and ankle extensor force quantified when running 4.0 m/s with four body-borne loads (20, 25, 30, and 35 kg). Peak normalized (BW) and unnormalized (N) extensor muscle force, relative effort, and joint angle and angular velocity at peak muscle force for both the ankle and the knee were submitted to a mixed model ANOVA. Results: Significant load by sex interactions for knee unnormalized extensor force (p = 0.025) and relative effort (p = 0.040) were observed, as males exhibited greater knee muscle force and effort than females and increased their muscle force and effort with additional load. Males also exhibited greater ankle normalized and unnormalized extensor force (p = 0.004, p \u3c 0.001) and knee unnormalized force than females (p = 0.005). The load increased the normalized ankle and knee muscle force (p \u3c 0.001, p = 0.030) and relative effort (p \u3c 0.001, p = 0.044) and the unnormalized knee muscle force (p = 0.009). Conclusion: Running with a load requires greater knee and ankle extensor force, but males exhibited greater increases in muscle force, particularly at the knee, than females

Markerless motion capture: What clinician-scientists need to know right now

National Institutes of Health R37-HD037985 provided tuition and stipend support for NI’s work. NIH R01-AR072034 provided stipend support for HBS and tuition and stipend support for KDS’s work. NIH F31-AR078580 and Foundation for Physical Therapy Research PODS II Scholarship provided tuition and stipend support for EKA's work.Peer reviewe

The Effect of Nordic Hamstring Strength Training on Muscle Architecture, Stiffness, and Strength

Purpose: Hamstring strain injury is a frequent and serious injury in competitive and recreational sports. While Nordic hamstring (NH) eccentric strength training is an effective hamstring injury prevention method, the protective mechanism of this exercise is not understood. Strength training increases muscle strength, but also alters muscle architecture and stiffness; all three factors may be associated with reducing muscle injuries. The purpose of this study was to examine the effects of NH eccentric strength training on hamstring muscle architecture, stiffness, and strength. Methods: Twenty healthy participants were randomly assigned to an eccentric training group or control group. Control participants performed static stretching, while experimental participants performed static stretching and NH training for 6 weeks. Pre- and post-intervention measurements included: hamstring muscle architecture and stiffness using ultrasound imaging and elastography, and maximal hamstring strength measured on a dynamometer. Results: The experimental group, but not the control group, increased volume (131.5 vs. 145.2 cm3, p\u3c0.001) and physiological cross-sectional area (16.1 vs. 18.1 cm2, p=0.032). There were no significant changes to muscle fascicle length, stiffness, or eccentric hamstring strength. Conclusions: The NH intervention was an effective training method for muscle hypertrophy, but, contrary to common literature findings for other modes of eccentric training, did not increase fascicle length. The data suggest the mechanism behind NH eccentric strength training mitigating hamstring injury risk could be increasing volume rather than increasing muscle length. Future research is therefore warranted to determine if muscle hypertrophy induced by NH training lowers future hamstring strain injury risk

Association Between Knee Anatomic Metrics and Biomechanics for Male Soldiers Landing with Load

Background: Anterior cruciate ligament (ACL) injury is a military occupational hazard that may be attributed to an individual’s knee biomechanics and joint anatomy. This study sought to determine if greater flexion when landing with load resulted in knee biomechanics thought to decrease ACL injury risk and whether knee biomechanics during landing relate to knee anatomic metrics. Hypothesis: Anatomic metrics regarding the slope and concavity of the tibial plateau will exhibit a significant relation to the increased anterior shear force on the knee and decreased knee flexion posture during landing with body-borne load. Study Design: Descriptive laboratory study. Methods: Twenty male military personnel completed a drop landing task with 3 load conditions: light (~6 kg), medium (15% body weight), and heavy (30% body weight). Participants were divided into groups based on knee flexion exhibited when landing with the heavy load (high- and low-Δflexion). Tibial slopes and depth were measured on weightbearing volumetric images of the knee obtained with a prototype cone beam computed tomography system. Knee biomechanics were submitted to a linear mixed model to evaluate the effect of landing group and load, with the anatomic metrics considered covariates. Results: Load increased peak proximal anterior tibial shear force (P = .034), knee flexion angle (P = .024), and moment (P = .001) during landing. Only the high flexion group increased knee flexion (P \u3c .001) during weighted landings with medium and heavy loads. The low flexion group used greater knee abduction angle (P = .030) and peak proximal anterior tibial shear force (P = .034) when landing with load. Anatomic metrics did not differ between groups, but ratio of medial-to-lateral tibial slope and medial tibial depth predicted peak proximal anterior tibial shear force (P = .009) and knee flexion (P = .034) during landing, respectively. Conclusion: Increasing knee flexion is an attainable strategy to mitigate risk of ACL injury, but certain individuals may be predisposed to knee forces and biomechanics that load the ACL during weighted landings. Clinical Relevance: The ability to screen individuals for anatomic metrics that predict knee flexion may identify soldiers and athletes who require additional training to mitigate the risk of lower extremity injury

Dataset for Evaluation of the Ankle Roll Guard’s Effectiveness to Improve Clinical Benefit

Ankle Roll Guard is a new, patent protected orthopedic product. The Ankle Roll Guard Armor1 provides an individual protection from “rolling” or spraining their ankle via a lightweight buttress on the lateral aspect of their shoe. This design prevents the ankle from rolling or inverting past 30 degrees, postures where injury is reported to occur, without placing mechanical restriction on the joint. This key innovation allows the user a natural, unrestricted ankle range of motion without compromising the product’s injury protection. Existing prophylactic products, however, provide ankle stability via mechanical restriction to the joint. While these prophylactic products are somewhat effective at preventing injury, the mechanical restriction impairs joint motion, often leading to the development of long-term ankle ailments. The Ankle Roll Guard, however, provides a critical solution to this issue. The product’s design allows the user protection from injury without the mechanical restriction of existing prophylactic products. Yet, because the Ankle Roll Guard is completely new, data regarding the product’s effectiveness is limited to anecdotal evidence provided by users. To target new consumers and stimulate company growth, Ankle Roll Guard needs independent scientific testing to validate the product’s effectiveness. With that in mind, researchers in Boise State University’s Center for Orthopaedic and Biomechanics sought to quantify and improve the Ankle Roll Guard’s effectiveness. Specifically, this effort quantified the effectiveness of the Ankle Roll Guard to prevent ankle inversion and compare its effectiveness with existing prophylactic products, including external brace, athletic tape and unbraced, control ankle, during a sudden inversion event and a battery of functional tasks. The experimental outcomes provided herein by Boise State researchers demonstrate the Ankle Roll Guard may prevent excessive ankle inversion, but not as effectively as “more” restrictive ankle prophylactics (in particular, Brace and Tape). Yet the Ankle Roll Guard’s design may provide mechanical stability necessary to prevent ankle sprain, without the deleterious impact on the user’s knee joint and functional performance routinely seen when wearing the more restrictive ankle prophylactics

Effectiveness of Novel Ankle Prophylactic Compared with Lace-Up Brace or Tape

Context: Conventional ankle prophylactics restrict harmful ankle inversion motions that lead to injury. But these existing prophylactics also limit other ankle motions, potentially leading to detriments in functional joint capacity. The ankle roll guard (ARG) may alleviate the prevailing issues of existing ankle prophylactics and prevent harmful ankle inversion, while allowing other joint motions. Objective: This technical report sought to compare the ARG’s ability to prevent ankle inversion, but not restrict other ankle motions with existing prophylactics. Design: Repeated-measures study. Setting: Motion capture laboratory. Participants: Thirty participants. Intervention: Each participant had dominant limb ankle kinematics recorded during 5 successful trials of a sudden inversion event and 30-cm drop landing task with each of 4 conditions (ARG, ASO ankle stabilizer [brace], closed-basket weave athletic tape [tape], and unbraced [control]). Main Outcome Measures: Peak ankle inversion angle, range of inversion motion (ROM), and time to peak inversion during the sudden inversion event, and ankle plantar- and dorsiflexion ROM during the drop landing were submitted to a 1-way repeated-measures analysis of variance to test the main effect of prophylaxis. Results: Participants exhibited greater inversion ROM with control compared with tape (P = .001), and greater plantar- and dorsiflexion ROM with ARG and control compared with brace (P = .02, P = .001) and tape (P = .02, P \u3c .001). It took significantly longer to reach peak ankle inversion with brace and tape compared with ARG (P \u3c .001, P = .001) and control (P = .01, P = .01). No significant difference in peak ankle inversion was observed between any condition (P \u3e .05). Conclusion: The ARG may prevent ankle inversion angles where injury is thought to occur (reportedly \u3e41°), but is less restrictive than existing prophylactics. The less restrictive ARG may make its use ideal during rehabilitation as it allows ankle plantar- and dorsiflexion motions, while preventing inversion related to injury