Trunk,pelvis and lower limb coordination between anticipated and unanticipated sidestep cutting in females

BackgroundEmerging research has suggested a plausible relationship may exist between lower limb coordination and musculoskeletal injury. A small number of studies have investigated the link between coordination and anterior cruciate ligament (ACL) injury during sidestep cutting. While prior work has shown unanticipated sidestep cutting to exhibit a more ‘at risk’ kinematic profile compared to anticipated tasks, a detailed understanding of the coordination between multiple joints and how they differ during unanticipated actions is lacking, particularly in females.Research questionThe purpose of this study was to observe the difference in trunk, pelvis and lower limb coordination and coordination variability during a dynamic, sidestep cutting task under anticipated and unanticipated conditions in a healthy female cohort.MethodsThree-dimensional motion analysis data were recorded during anticipated and unanticipated sidestep cutting for nineteen healthy female participants (age, 24 ± 3yrs; height, 164 ± 5 cm; and weight, 58 ± 6 kg). Vector coding methodology was used to calculate coordination and coordination variability values and statistical parametric and non-parametric mapping was used to comprehensively determine differences between anticipated and unanticipated conditions.ResultsDifferences were observed between anticipated and unanticipated conditions in the hip flexion – knee abduction angle (89 % of stance), hip rotation – knee abduction angle (55 % of stance), knee flexion – knee abduction angle (81–83 %, 86 % and 88–89 %) and knee flexion – ankle flexion angle (14–18 %) coupling angles. Differences in coupling angle variability were also observed with only one cluster of significance seen in hip abduction – knee abduction variability (27–30 % of stance).SignificanceHealthy females exhibit significant differences in lower limb coupling angles and coupling angle variability between anticipated and unanticipated sidestep cutting. Interventions aimed at reducing ACL injury risk may need to consider that anticipated and unanticipated sidestep cutting tasks present unique demands, and therefore should both be trained specifically.     

An analysis of the sidestep cutting manoeuvre

The sidestep cutting manoeuvre is a common mechanism of noncontact or isolated ACL ruptures in athletes. We analyzed the amount and direction of tibial rotation that occurred at the knee joint with a triaxial electrogoniometer on 11 male subjects who performed the sidestep cutting manoeuvre. The mean total tibial rotation was 19.84 +/- 5.63 degrees and the mean maximum point of internal tibial rotation occurred at 34.77 +/- 5.30% of the stance phase. However, greater values for internal tibial rotation occurred in the swing phase in association with a greater angle of knee flexion. Therefore, in our subjects, during the sidestep cutting manoeuvre, internal tibial rotation did occur at the knee but was not maximal. Under normal circumstances when performing the sidestep cutting manoeuvre, maximum internal tibial rotation does not occur and so the ACL is not placed under excessive strain in such a manoeuvre. If the ACL ruptures during a sidestep cutting manoeuvre then a possible cause may be the athlete's loss of the ability to control internal tibial rotation of the knee.     

Anticipatory effects on knee joint loading during running and cutting maneuvers.

PURPOSE: To determine how unanticipated performance of cutting maneuvers in sport affects the external loads applied to the knee joint and the potential risk for ligament injury. METHODS: A 50-Hz VICON motion analysis system was used to determine the lower limb kinematics of 11 healthy male subjects during running and cutting tasks performed under preplanned (PP) and unanticipated (UN) conditions. Subjects performed the UN tasks in response to a light stimulus on a target board. A kinematic model was then used in conjunction with force place data to calculate the three-dimensional loads at the knee joint. RESULTS: External flexion/extension moments at the knee joint were similar between PP and UN conditions; however, the varus/valgus and internal/external rotation moments during the UN cutting tasks were up to twice the magnitude of the moments measured during the PP condition. CONCLUSION: Cutting maneuvers performed without adequate planning may increase the risk of noncontact knee ligament injury due to the increased external varus/valgus and internal/external rotation moments applied to the knee. These results are probably due to the small amount of time to make appropriate postural adjustments before performance of the task, such as the position of the foot on the ground relative to the body center of mass. Subsequently, training for the game situation should involve drills that familiarize players with making unanticipated changes of direction. Practice sessions should also incorporate plyometrics and should focus on better interpretation of visual cues to increase the time available to preplan a movement.     

Gender differences in the kinematics of unanticipated cutting in young athletes

PURPOSE: Anterior cruciate ligament (ACL) injuries occur at a greater rate in adolescent females compared with males who participate in the same pivoting and jumping sports. The purpose of this study was to compare knee and ankle joint angles between males and females during an unanticipated cutting maneuver. The hypotheses were that female athletes would display increased knee abduction, increased ankle eversion and decreased knee flexion during the unanticipated cutting maneuver compared with males. METHODS: Fifty-four male and 72 adolescent female middle and high school basketball players volunteered to participate in this study. Knee and ankle kinematics were calculated using three-dimensional motion analysis during a jump-stop unanticipated cut (JSUC) maneuver. RESULTS: Females exhibited greater knee abduction (valgus) angles compared with males. Gender differences were also found in maximum ankle eversion and maximum inversion during stance phase. No differences were found in knee flexion angles at initial contact or maximum. CONCLUSION: Gender differences in knee and ankle kinematics in the frontal plane during cutting may help explain the gender differences in ACL injury rates. Implementation of dynamic neuromuscular training in young athletes with a focus on frontal plane motion may help prevent ACL injuries and their long-term debilitating effects.     

Biomechanical differences related to leg dominance were not found during a cutting task

Previous studies have shown conflicting information regarding leg dominance as an etiological factor for the risk of anterior cruciate ligament (ACL) injuries. It remains unclear if lower extremity neuromechanical limb asymmetries exist in experienced athletes. The purpose of this study was to evaluate lower extremity neuromechanical effects of leg dominance in female collegiate soccer athletes during an unanticipated side‐step cutting task. Twenty female collegiate soccer players completed an unanticipated side‐step cutting task, using their dominant and non‐dominant legs. Kinematic and kinetic data were collected to quantify joint angles and forces, with wireless electromyography (EMG) quantifying muscle activity. MANOVA's were conducted to determine the effect of leg dominance on hip and knee mechanics at and between pre‐contact, initial contact, peak knee adduction moment, and peak stance periods. Dependent variables consisted of peak time occurrences, hip and knee rotations and moments, ground reaction force, EMG amplitudes, stance time, and approach velocity. No significant differences were found for any variables at or between the periods of interest. Collegiate female soccer athletes exhibit similar movement patterns between dominant and non‐dominant legs while performing a side‐step cutting task, suggesting that leg dominance does not adversely influence known biomechanical non‐contact ACL risk factors.     

Factors affecting selected reciprocal muscle group ratios in preadolescents

This study examines the influence of limb velocity and lateral dominance on the relationship between the knee flexors and extensors. Thirty preadolescents, 18 male and 12 female, performed a series of reciprocal knee flexion-extension movements on the Cybex II isokinetic system. The tests were performed at a range of selected velocities and on both dominant and nondominant limbs. The agonist-antagonist ratios considered were the peak torque ratios, the torque ratio produced at specific angles, and the ratio comparing the total work performed by the hamstrings with that of the quadriceps. The results showed that an increased limb velocity produces a significant increase in the peak torque and work ratios (P less than 0.05), limb velocity has no significant effect on the torque ratio produced at 30 degrees and 60 degrees in the preadolescents, and lower limb lateral dominance has no significant effect on the three ratios examined.     

Hip and knee muscle torque is not impaired in the first three months of a first-time lateral ankle sprain

ObjectivesThe primary objective was to compare hip and knee isometric muscle strength between individuals with a first-time acute lateral ankle sprain and controls. A secondary objective was to investigate hip and knee isometric muscle strength three months post-injury.DesignCross-sectional and prospective follow-up components.SettingLaboratory environment.ParticipantsForty-two participants (21 acute lateral ankle sprain and 21 controls) matched for age, sex, physical activity and leg dominance participated.Main outcome measuresHip and knee isometric muscle torque was assessed using a rigidly fixated hand-held dynamometer. Testing in acute lateral ankle sprain participants was performed within four weeks of injury and three months post-injury. Controls were tested at one timepoint.ResultsThere were no differences in hip or knee isometric muscle torque between acute lateral ankle sprain and control participants (mean differences <0.08). Hip and knee isometric muscle torque in acute ankle sprain participants did not differ between baseline and three months post-injury testing (mean difference <0.06).ConclusionsProximal lower limb isometric strength is not impaired within the first three months of sustaining a first-time lateral ankle sprain injury. This implies that hip and knee isometric strength deficits in individuals with CAI may occur at some later stage.     

Electromyographic timing analysis of forward and backward cycling

PURPOSE: Backward walking to running progressions are becoming a popular, nontraditional component of functional knee rehabilitation programs. The purpose of this electromyographic (EMG) and motion analysis study was to compare the activation duration of the vastus medialis, vastus lateralis, rectus femoris, medial hamstrings, lateral hamstring, tibialis anterior, and gastrocnemius muscles during forward and backward cycling. We hypothesized that the hamstrings would demonstrate greater activation duration during backward cycling. METHODS: The right lower extremity of 12 healthy subjects (6 male and 6 female) was instrumented with surface EMG electrodes and retroreflective markers to confirm lower extremity kinematic consistency between conditions. RESULTS: Statistical analysis of hip, knee, and ankle kinematics (200 Hz sampling rate) and gender failed to reveal significant differences between conditions (P > 0.05). Quadrant analysis of muscle activation duration with Bonferroni corrections for multiple comparisons revealed that medial and lateral hamstring activation duration was greater during the early recovery phase (quadrant III) of backward cycling than forward cycling (P < 0.00156). Rectus femoris activation duration was greater in the early propulsive phase of backward cycling (quadrant 1) (P < 0.00156) and in the early recovery phase of forward cycling (quadrant III) (P < 0.00156). CONCLUSIONS: These findings lend support for the use of backward cycling during the early recovery phase (quadrant III) to achieve a selective hamstring muscle response of relatively decreased patellofemoral stress and anterior cruciate ligament strain.     

The drop-jump screening test: difference in lower limb control by gender and effect of neuromuscular training in female athletes

BACKGROUND: A valgus lower limb alignment has been noted during noncontact anterior cruciate ligament injuries. A video drop-jump test can indicate an athlete's ability to control lower limb axial alignment in the coronal plane. HYPOTHESES: Female athletes have decreased knee separation distances on landing and acceleration; male athletes have a neutrally aligned lower limb position. A neuromuscular training program will significantly increase knee separation distance in female athletes. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: The authors tested 325 female and 130 male athletes aged 11 to 19 years. The distance between the hips, knees, and ankles was measured during a drop-jump test. The separation distance between the knees and ankles was normalized by the hip separation distance. A neuromuscular training program (Sportsmetrics) was completed by 62 female athletes, and their jump-landing characteristics were reexamined. RESULTS: A marked decrease in knee separation distance was found on takeoff in 80% of female athletes and in 72% of male athletes. There was no difference between male and female athletes in the normalized knee and ankle separation distance during the landing and takeoff phases. The knee separation distance on landing was 23 +/- 9 cm in the female athletes and 22 +/- 8 cm in the male athletes. The normalized knee separation distance was 51% +/- 19% in the female athletes and 51% +/- 15% in the male athletes. After training, statistically significant increases were found in the female athletes in the knee separation distance on landing (29 +/- 8 cm, P < .0001) and in the normalized knee separation distance (68% +/- 18%, P < .0001). The trained female athletes had significantly greater knee separation distance and normalized knee separation distance than did the males (P < .0001). CONCLUSIONS: The majority of untrained female and male athletes demonstrated a valgus alignment appearance on the video test. After neuromuscular training, female athletes had improved knee separation distances and a more neutral lower limb alignment on landing and takeoff.     

Effects of a dynamic core stability program on the biomechanics of cutting maneuvers: A randomized controlled trial

Deficits in trunk control predict ACL injuries which frequently occur during high‐risk activities such as cutting. However, no existing trunk control/core stability program has been found to positively affect trunk kinematics during cutting activities. This study investigated the effectiveness of a 6‐week dynamic core stability program (DCS ) on the biomechanics of anticipated and unanticipated side and crossover cutting maneuvers. Thirty‐one male, varsity footballers participated in this randomized controlled trial. Three‐dimensional trunk and lower limb biomechanics were captured in a motion analysis laboratory during the weight acceptance phase of anticipated and unanticipated side and crossover cutting maneuvers at baseline and 6‐week follow‐up. The DCS group performed a DCS program three times weekly for 6 weeks in a university rehabilitation room. Both the DCS and control groups concurrently completed their regular practice and match play. Statistical parametric mapping and repeated measures analysis of variance were used to determine any group (DCS vs control) by time (pre vs post) interactions. The DCS resulted in greater internal hip extensor (P =.017, η²=0.079), smaller internal knee valgus (P =.026, η²=0.076), and smaller internal knee external rotator moments (P =.041, η²=0.066) during anticipated side cutting compared with the control group. It also led to reduced posterior ground reaction forces for all cutting activities (P =.015‐.030, η²=0.074‐0.105). A 6‐week DCS program did not affect trunk kinematics, but it did reduce a small number of biomechanical risk factors for ACL injury, predominantly during anticipated side cutting. A DCS program could play a role in multimodal ACL injury prevention programs.     

The effect of knee brace on coordination and neuronal leg muscle control: an early postoperative functional study in anterior cruciate ligament reconstructed patients

Two studies were carried out after anterior cruciate ligament (ACL) reconstruction to determine the effect of a knee brace on coordination (test 1) and electromyographic muscle activity in drop jumps (test 2). Test 1 studied 25 patients with ACL reconstruction under three test conditions (one-leg static, two-legged static, two-legged dynamic) compared with a control (n=30). The results showed highly significant improvements in all braced conditions. In test 2 ten patients with ACL reconstruction and ten healthy subjects performed a two-legged drop-jump; this was repeated 15 times and again 15 times with a knee brace worn on the reconstructed limb. Changes in electromyographically determined muscle activity (vastus medialis, vastus lateralis, biceps femoris, gastrocnemius) were observed, but they were significant in only few cases because of high variability. Drop-jumps with knee brace improved jumping height, increased the maximum knee angle in the ground contact phase, and reduced the maximum knee angle in the landing phase. Patients thus develop an increased confidence in the stability of their knees. We conclude that the benefits of the knee brace are due to the mechanical action, an enhanced coordination, and a psychological effect.     

Muscle activation strategies at the knee during running and cutting maneuvers

PURPOSE: The purpose of this article was to investigate the activation patterns of muscles surrounding the knee during preplanned (PP) and unanticipated (UN) running and cutting tasks, with respect to the external moments applied to the joint. It was hypothesized that activation strategies during PP tasks would correspond to the magnitude and direction of the external loads applied to the knee joint, and the muscle activation patterns would differ between PP and UN tasks. METHODS: Eleven healthy male subjects performed a series of running and cutting tasks under PP and UN conditions. Activation from 10 knee muscles were determined using full-wave rectified, filtered, and normalized EMG calculated during a precontact phase and two epochs across the stance phase. Knee joint flexor and extensor muscle group ratios indicated the level of co-contraction. Individual muscles were also grouped into medial/lateral and internal/external rotation muscle groups, based upon their ability to counter externally applied varus/valgus and internal/external rotation joint loads, respectively. RESULTS: Selective activation of medial/lateral and internal/external rotation muscles and co-contraction of flexors and extensors were used to stabilize the joint under PP conditions, whereas generalized co-contraction strategies were employed during the UN condition. Net muscle activation during the UN sidestepping tasks increased by 10-20%, compared with an approximately 100% increase in applied varus/valgus and internal/external rotation joint moments. CONCLUSION: In PP conditions, activation patterns appear to be selected to support the external loads experienced at the knee, e.g., medial muscles activated to resist applied valgus moments. Under UN conditions, there was no selective activation of muscles to counter the external knee load, with generalized co-contraction being the activation pattern adopted. These findings have implications for the etiology of noncontact knee ligament injuries.     

Early and late rate of force development: differential adaptive responses to resistance training?

The objective was to analyze muscle activity and movement patterns during landing of a single leg hop for distance after anterior cruciate ligament (ACL) reconstruction. Nine (six males, three females) ACL-reconstructed patients 6 months after surgery and 11 (eight males, three females) healthy control subjects performed the hop task. Electromyographic signals from lower limb muscles were analyzed to determine onset time before landing. Biomechanical data were collected using an Optotrak Motion Analysis System and force plate. Matlab was used to calculate kinetics and joint kinematics. Side-to-side differences in ACL-reconstructed patients and healthy subjects as well as differences between the patients and control group were analyzed. In ACL-reconstructed limbs, significantly earlier onset times were found for all muscles, except vastus medialis, compared with the uninvolved side. The involved limbs had significantly reduced knee flexion during the take-off and increased plantarflexion at initial contact. The knee extension moment was significantly lower in the involved limb. In the control group, significantly earlier onset times were found for the semitendinosus, vastus lateralis and medial gastrocnemius of the non-dominant side compared with the dominant side. Muscle onset times are earlier and movement patterns are altered in the involved limb 6 months after ACL reconstruction.     

Comparison of frontal plane trunk kinematics and hip and knee moments during anticipated and unanticipated walking and side step cutting tasks

BACKGROUND: Frontal plane trunk and lower extremity adjustments during unanticipated tasks are hypothesized to influence hip and knee neuromuscular control, and therefore, contribute to anterior cruciate ligament (ACL) injury risk. The aims of this study were to examine frontal plane trunk/hip kinematics and hip and knee moments (measures of neuromuscular control) during unanticipated straight and side step cut tasks. METHODS: Kinematic and kinetic variables were collected while subjects performed two anticipated tasks, including walking straight (ST) and side step cutting (SS), and two unanticipated tasks (STU and SSU). Foot placement, thorax-pelvis-hip kinematic variables and hip and knee moments were calculated over the first 30% of stance. FINDINGS: Hip abduction angles and knee moments were significantly affected by task and anticipation. Hip abduction angles decreased, by 4.0-7.6 degrees , when comparing the SSU task to the ST, STU and SS tasks. The hip abduction angles were associated with foot placement and lateral trunk orientation. INTERPRETATION: Hip abduction angles and foot placement, not lateral trunk flexion influence trunk orientation. Anticipation influences hip and knee neuromuscular control and therefore may guide the development of ACL prevention strategies.     

An electromyographic analysis of sumo and conventional style deadlifts

PURPOSE: Strength athletes often employ the deadlift in their training or rehabilitation regimens. The purpose of this study was to compare muscle activity between sumo and conventional style deadlifts, and between belt and no-belt conditions. METHODS: Six cameras collected 60-Hz video data and 960-Hz electromyographic data from 13 collegiate football players who performed sumo and conventional deadlifts with and without a lifting belt, employing a 12-RM intensity. Variables measured were knee angles and EMG measurements from 16 muscles. Muscle activity were averaged and compared within three 30-degree knee angle intervals from 90 to 0 degrees during the ascent, and three 30-degree knee angle intervals from 0 to 90 degrees during the descent. RESULTS: Overall EMG activity from the vastus medialis, vastus lateralis, and tibialis anterior were significantly greater in the sumo deadlift, whereas overall EMG activity from the medial gastrocnemius was significantly greater in the conventional deadlift. Compared with the no-belt condition, the belt condition produced significantly greater rectus abdominis activity and significantly less external oblique activity. For most muscles, EMG activity was significantly greater in the knee extending intervals compared with the corresponding knee flexing intervals. Quadriceps, tibialis anterior, hip adductor, gluteus maximus, L3 and T12 paraspinal, and middle trapezius activity were significantly greater in higher knee flexion intervals compared with lower knee flexion intervals, whereas hamstrings, gastrocnemius, and upper trapezius activity were greater in lower knee flexion intervals compared with higher knee flexion intervals. CONCLUSIONS: Athletes may choose to employ either the sumo or conventional deadlift style, depending on which muscles are considered most important according to their training protocols. Moderate to high co-contractions from the quadriceps, hamstrings, and gastrocnemius imply that the deadlift may be an effective closed kinetic chain exercise for strength athletes to employ during knee rehabilitation.     

Relationship between lower limb EMG activity and knee frontal plane projection angle during a single-legged drop jump

ObjectivesTo assess a relationship between lower limb muscle activity and the frontal plane knee kinematics during a single-legged drop jump.DesignCorrelation study;SettingFunctional Anatomy Laboratory.Participants35 healthy collegiate male athletes.Main outcome measuresMuscle activity (%MVIC) of gluteus maximus, gluteus medius, biceps femoris, semitendinosus, vastus medialis quadriceps, vastus lateralis quadriceps, medial gastrocnemius and lateral gastrocnemius; peak knee frontal plane projection angle; and Pearson's correlation coefficients between muscle activity and peak knee frontal plane projection angle. All outcomes were assessed for both dominant and non-dominant limbs.ResultsSignificant correlations (r = 0.46–0.60, P < 0.05) were found between the muscle activities of the gluteus maximus, gluteus medius, biceps femoris, and semitendinosus, when compared to the knee frontal plane projection angle.ConclusionGluteal muscles and hamstring muscles are associated with the peak knee frontal plane projection angle during a single-legged drop jump test. Thus, gluteal and hamstring muscle activities should be considered when developing rehabilitation or injury prevention programs.     

Knee joint laxity and neuromuscular characteristics of male and female soccer and basketball players.

Anterior cruciate ligament injuries are occurring at a higher rate in female athletes compared with their male counterparts. Research in the area of anterior cruciate ligament injury has increasingly focused on the role of joint proprioception and muscle activity in promoting knee joint stability. We measured knee joint laxity, joint kinesthesia, lower extremity balance, the amount of time required to generate peak torque of the knee flexor and extensor musculature, and electromyographically assessed muscle activity in 34 healthy, collegiate-level athletes (average age, 19.6 +/- 1.5 years) who played soccer or basketball or both. Independent t-tests were used to determine significant sex differences. Results revealed that women inherently possess significantly greater knee joint laxity values, demonstrate a significantly longer time to detect the knee joint motion moving into extension, possess significantly superior single-legged balance ability, and produce significantly greater electromyographic peak amplitude and area of the lateral hamstring muscle subsequent to landing a jump. The excessive joint laxity of women appears to contribute to diminished joint proprioception, rendering the knee less sensitive to potentially damaging forces and possibly at risk for injury. Unable to rely on ligamentous structures, healthy female athletes appear to have adopted compensatory mechanisms of increased hamstring activity to achieve functional joint stabilization.     

Changes in muscle activation patterns when running step rate is increased

Running with a step rate 5-10% greater than one's preferred can substantially reduce lower extremity joint moments and powers, and has been suggested as a possible strategy to aid in running injury management. The purpose of this study was to examine how neuromuscular activity changes with an increase in step rate during running. Forty-five injury-free, recreational runners participated in this study. Three-dimensional motion, ground reaction forces, and electromyography (EMG) of 8 muscles (rectus femoris, vastus lateralis, medial gastrocnemius, tibialis anterior, medial and lateral hamstrings, and gluteus medius and maximus) were recorded as each subject ran at their preferred speed for three different step rate conditions: preferred, +5% and +10% of preferred. Outcome measures included mean normalized EMG activity for each muscle at specific periods during the gait cycle. Muscle activities were found to predominantly increase during late swing, with no significant change in activities during the loading response. This increased muscle activity in anticipation of foot-ground contact likely alters the landing posture of the limb and the subsequent negative work performed by the joints during stance phase. Further, the increased activity observed in the gluteus maximus and medius suggests running with a greater step rate may have therapeutic benefits to those with anterior knee pain.     

Effect of gait retraining for reducing ambulatory knee load on trunk biomechanics and trunk muscle activity

The purpose of this study was to test the hypothesis that walking with increased medio-lateral trunk sway is associated with lower external knee adduction moment and lower extremity muscle activation, and higher external ipsilateral trunk moment and trunk muscle activity than walking with normal trunk sway in healthy participants. Fifteen participants performed walking trials with normal and increased medio-lateral trunk sway. Maximum trunk sway, first maximum knee adduction moment, lateral trunk bending moment, and bilateral vastus medialis, vastus lateralis, gluteus medius, rectus abdominis, external oblique and erector spinae muscle activity were computed. Walking with increased trunk sway was associated with lower maximum knee adduction moment (95% confidence interval (CI): 0.50–0.62 Nm/kg vs. 0.62–0.76 Nm/kg; P < .001) and ipsilateral gluteus medius (−17%; P = .014) and erector spinae muscle activity (−24%; P = .004) and greater maximum lateral trunk bending moment (+34%; P < .001) and contralateral external oblique muscle activity (+60%; P = .009). In all participants, maximum knee adduction moment was negatively correlated and maximum trunk moment was positively correlated with maximum trunk sway. The results of this study suggest that walking with increased trunk sway not only reduces the external knee adduction moment but also alters and possibly increases the load on the trunk. Hence, load-altering biomechanical interventions should always be evaluated not only regarding their effects on the index joint but on other load-bearing joints such as the spine.