Increased core stability is associated with reduced knee valgus during single-leg landing tasks: Investigating lumbar spine and hip joint rotational stiffness.

Knee valgus during landing has been identified as a strong correlate of ACL injury. Inappropriate trunk control during landing contributes to high knee valgus, with neuromuscular factors related to core stability postulated as the mechanism. This investigation probed the influence of trunk and hip mechanics, including joint stiffness, on knee mechanics, particularly high knee valgus. Specifically, this study quantified lumbar spine and hip joint rotational stiffness (a proxy for mechanical joint stability) during single-leg landing tasks known to be associated with injury risk, particularly in females. Kinematics, kinetics, and 24 channels of electromyography spanning the trunk and hip musculature were measured in 18 healthy female participants. Anatomically detailed EMG-driven musculoskeletal models quantified lumbar spine and hip joint rotational stiffness. The links between peak knee abduction angle and moment with lumbar spine and hip joint rotational stiffness were measured. Hip joint rotational stiffness influenced knee abduction across tasks (correlation coefficient ranging from -0.48 to -0.70, p < 0.05) to reduce valgus deviation. Similarly, transverse plane hip joint rotational stiffness during landings reduced knee abduction moment (R = -0.50, P = 0.03; R = -0.49, P = 0.04), and lumbar spine joint rotational stiffness reduced knee abduction angle and moment but did not consistently reach statistical significance. The control system uses stiffness to control motion. This study demonstrates the importance of proximal (lumbar spine and hip) joint rotational stiffness (i.e. core control stability) during single-leg landing to prevent knee abduction motion. Instantaneous core stability is achieved with the coordinated activation and stiffness of both trunk and hip muscles.

Anterior Cruciate Ligament Injury Mechanisms and the Kinetic Chain Linkage: The Effect of Proximal Joint Stiffness on Distal Knee Control During Bilateral Landings.

BACKGROUND: Neuromuscular deficits at the trunk and hip may contribute to dynamic knee valgus and anterior cruciate ligament injury mechanisms. However, comprehensive examination of neuromuscular patterns and their mechanical influence is lacking. OBJECTIVES: To investigate the influence of lumbar spine joint rotational stiffness (JRS) and the gluteal musculature contribution to hip JRS on dynamic knee valgus. METHODS: In this cross-sectional study, 18 university-aged women completed a drop vertical jump while we measured kinematics, kinetics, and 24 channels of electromyography (EMG) spanning the trunk and hip musculature. We classified each limb as high or low valgus, based on frontal plane knee displacement magnitude. We used anatomically detailed, EMG-driven biomechanical models to quantify lumbar spine JRS and muscle contributions to hip JRS. RESULTS: Low-valgus limbs generated greater gluteus medius frontal JRS (P = .002; effect size, 1.3) and gluteus maximus transverse JRS (P = .003; effect size, 1.2) compared to high-valgus limbs. Participants with bilateral high-valgus collapse had substantially reduced lumbar spine sagittal JRS compared to the group with low valgus on both limbs (P = .05; effect size, 5.1). Those with low valgus on both limbs also had a peak lumbar spine flexion angle of 24° ± 4°, compared to the bilateral high-valgus group's angle of 38° ± 10° (P = .09; effect size, 1.8). CONCLUSION: Participants who avoided high medial knee displacement had greater proximal JRS. Increased JRS at the lumbar spine and greater JRS contributions from the gluteal musculature are linked with preventing high medial knee displacement. J Orthop Sports Phys Ther 2019;49(8):601-610. Epub 26 May 2019. doi:10.2519/jospt.2019.8248.

New Approach in Assessing Core Muscle Endurance Using Ratings of Perceived Exertion.

George, JD, Tolley, JR, Vehrs, PR, Reece, JD, Akay, MF, and Cambridge, EDJ. New approach in assessing core muscle endurance using ratings of perceived exertion. J Strength Cond Res 32(4): 1081-1088, 2018-This study sought to develop regression models to estimate maximal endurance time using data from 4 core muscle endurance tests. Eighty healthy university students (age: 22.7 ± 1.9 years) performed the plank, right side-bridge, left side-bridge, and back extension tests in a random order. Participants were instructed to hold each static position for a maximal endurance time, while maintaining proper form, and then rest for 5 minutes between tests. A test administrator recorded participants' ratings of perceived exertion (RPE; a modified 10-point scale) every 5 seconds. Based on regression analysis, the elapsed time to reach an RPE of 8 (RPE8) exhibited statistical significance (p < 0.0001) and the highest accuracy as compared with lower RPE values. The following univariate regression models were generated to estimate maximal endurance time across the 4 tests: plank (r = 0.94; standard error of estimate [SEE] = 17.6 seconds; n = 77) = 23.9 + (1.110 × RPE8); right side-bridge (r = 0.92; SEE = 11.4 seconds; n = 80) = 18.5 + (1.022 × RPE8); left side-bridge (r = 0.93; SEE = 10.8 seconds; n = 80) = 16.8 + (1.062 × RPE8); and back extension (r = 0.93; SEE = 14.2 seconds; n = 79) = 21.5 + (1.027 × RPE8). These results suggest that submaximal protocols based on elapsed time to reach RPE8 provide strength and conditioning professionals relatively accurate univariate regression equation estimates of maximal core muscle endurance time and offer a viable submaximal alternative to maximal capacity testing when time efficiency, participant safety, or certain educational objectives may be a priority.

A six-week trial of hula hooping using a weighted hoop: effects on skinfold, girths, weight, and torso muscle endurance.

Novel ideas for core endurance training are continually being created. However, studies of their mechanism of action assist in evaluation of their potential as a training tool, for a variety of people and purposes. The specific purpose of this study was to evaluate a weighted hula hooping training program for its efficacy on improving core muscular endurance and influence on measures of body composition. Eighteen women participated in a weighted hula hooping trial lasting 6 weeks, although only 13 returned for posttrial re-assessment. Hip and waist circumferences, 5 torso muscle endurance tests, and 5 skinfold measurements ("sum of 5") were measured before and after the exercise program. Paired samples t-tests were performed to examine pre/post changes. On average, participants experienced a significant decrease in waist and hip circumference -3.4 cm (p < 0.01) and -1.4 cm (p ≤ 0.05), respectively and waist-to-hip ratio from 89.3 cm down to 87.3 cm (t = 3.312, p < 0.01). There were no significant changes in torso muscular endurance after the 6 weeks of hooping; however, the average "sum of 5" skinfold measurements increased by 10.5 cm (p ≤ 0.05). This study of weighted hula hooping suggested that regular hooping was associated with reduced waist and hip girth together with a redistribution of body mass; however, there were no improvements in torso muscular endurance as measured by isometric testing.

Examining the effects of altering hip orientation on gluteus medius and tensor fascae latae interplay during common non-weight-bearing hip rehabilitation exercises.

BACKGROUND: Improving activity and strength of the gluteus medius muscle is a common goal among clinicians aiming to rehabilitate lower extremity and low back injuries. The functional anatomy of the hip is complex, particularly how position-dependent the activity and strength of many muscles surrounding the hip are, and the optimal exercise technique to isolate gluteus medius remains controversial. The objective of this study was to quantify the effect of altering hip orientation during side-lying clamshell and hip abduction exercises on the relative muscle activation profiles of gluteus medius and tensor fascae latae. METHODS: The ratio of gluteus-medius-to-tensor-fascae-latae peak electromyography signal amplitude of 13 healthy, male participants was compared across variations of the clamshell and abduction exercises. The hip flexion angle was varied from 30°, 45°, and 60° for the clamshell, while hip rotation orientation was varied from internal, neutral, and external rotation for the abduction exercise. FINDINGS: Varying hip angle - flexion in the clamshell exercise and internal/external rotation in the abduction exercise - did not significantly affect the interplay between gluteus medius and tensor fascae latae activation levels. Both exercises remained gluteus medius-dominant across all variations, but the gluteus-medius-to-tensor-fascae-latae ratio was far greater for the clamshell than for the abduction exercise; the clamshell may be the preferred rehabilitative exercise to prescribe when minimal tensor fascae latae muscle activation is desired by the clinician. INTERPRETATION: These findings provide information for clinical decision-making pertaining to effective gluteus medius activation in lower extremity and low back exercise rehabilitation programs.

Isometric torso muscle endurance profiles in adolescents aged 15-18: normative values for age and gender differences.

OBJECTIVE: The aim of this study was to establish normative values for torso muscle endurance in adolescents aged 15-18 years. It was hypothesized that torso endurance profiles of adolescents differs between males and females and between adolescents and adults. BACKGROUND: Decreased torso muscle endurance has been identified as a potential personal risk factor for low back pain development in both adolescents and later years together with being detrimental for athletic performance. DESIGN: Measurement of torso muscle endurance, established through four tests performed in random order in a healthy adolescent population. SETTING: High school in Novi Sad, Province of Vojvodina, Republic of Serbia. METHODS: Two hundred and ninety-four adolescents from one high school (178 males and 116 females) were grouped into four age strata. Selected isometric torso muscle endurance tests were: Biering-Sørensen test for extensor endurance; Flexor endurance test; right and left Side Bridge tests. The mean, ratio, standard deviation and 25th, 50th and 75th percentile scores were determined for each gender/age strata. RESULTS AND CONCLUSION: Males had higher lateral torso endurance than females. Adolescents in general demonstrate their peak lifetime endurance as they appear more endurable than children and comparable adult groups. These data of endurance times, their ratios and percentiles in healthy normal subjects form a database bridging existing data for children and adults that may be useful for guiding training and rehabilitation.

Progressive hip rehabilitation: the effects of resistance band placement on gluteal activation during two common exercises.

BACKGROUND: A critical issue for constructing a progressive rehabilitation program is the knowledge of muscle activation levels across exercises and within exercise modifications. Many exercises are offered to enhance gluteal muscle activation during functional rehabilitation but little data exists to guide the progression of exercise intensity during rehabilitation. The objective of this paper was to examine the effects of altering resistance band placement during 'Monster Walks' and 'Sumo Walks.' METHODS: Nine healthy male volunteers formed a convenience sample. Sixteen electromyography channels measured neural drive of selected muscles of the right hip and torso muscles. Three resistance band placements (around the knees, ankles and feet) during the two exercises were utilized to provide a progressive resistance to the gluteal muscles while repeated measures ANOVA with Bonferroni adjustment was used to assess differences in mean EMG. The presentation of exercises and band placement were randomized. FINDINGS: Examining muscle activation profiles in the three hip muscles of interest revealed the progressive nature of the neural drive when altering band placement. Tensor fascia latae (TFL) demonstrated a progressive activation moving the band from the knee to the distal band placement, but not between the ankle and foot placements. Gluteus medius demonstrated a progressive activation moving distally between band placements. Gluteus maximus was preferentially activated only during the foot placement. INTERPRETATION: The band placements offered a progressive increase in resistance for hip rehabilitation, specifically the gluteal muscles. The added benefit of placing the band around the forefoot was selective enhancement of the gluteal muscles versus TFL presumably by adding an external rotation effort to the hips. This information may assist those who address gluteal activation patterns for patients suffering hip and back conditions where gluteal activation has been affected.

Comparison of force development strategies of spinal manipulation used for thoracic pain.

INTRODUCTION: To date, there is a paucity of comparative analysis of manual therapeutic procedures for the treatment of pain in the same spinal region. This paper examines the cross correlation of force-time histories across three distinct strategies of force production for the same thoracic spine procedure. Secondary analysis includes examination of the characteristics that account for potential differences. METHODS: A homogeneous sample of 21 male volunteers and three clinicians were selected as a convenience sample. The force-time histories were recorded using a table mounted force plate (AMTI model number OR6-7-2000, London, ON), and cross-correlation analysis was applied by strategy type, for analysis between group data. Secondary parameters included: peak force, preload force, slope of the thrust, instantaneous loading rate and thrust duration, of the total force magnitude. RESULTS: Primary results indicate strong correlations among all strategies but with notably different cross-correlation coefficients (0.894 ≤ r ≤ 0.946) based on individual comparisons. Classical descriptive components of the force-time curves (e.g. preload, peak force, slope) for each strategy group were examined. Significant differences in the raw data were noted on slope and loading rate (adjusted p < 0.01). One strategy of force development was significantly different from the others in four of the five characteristics. The effects of clinician stature were evaluated by normalizing force to body mass. CONCLUSION: Quantitative biomechanical differences in procedures may be responsible for differences in outcomes based on the method of treatment selected. This data set begins a basis for translational research to assist in identifying populations of thoracic spine pain patients for whom one procedure or other may be more effective.

Analysis of surface EMG spike shape across different levels of isometric force.

This research evaluated changes in surface electromyographic (SEMG) spike shape across different levels of isometric force. Ninety-six subjects generated three 5-s isometric step contractions of the elbow flexors at 40, 60, 80, and 100% of maximal voluntary contraction (MVC). Force and bipolar SEMG activity were monitored concurrently. The mean spike amplitude (MSA) exhibited a linear increase across the four levels of force. The mean spike frequency (MSF) remained stable from 40 to 80% of MVC; it then decreased from 80 to 100% of MVC. There was a concomitant increase in mean spike slope (MSS) that indicates that the biceps brachii (BB) relied on the recruitment of higher threshold motor units (MUs) from 40 to 80% of MVC. However, there progressive decrease in the mean number of peaks per spike (MNPPS) that suggests that MU synchronization was additionally required to increase force from 80 to 100% of MVC. The spike shape measures, taken together, indicate that the decrease in frequency content of the signal was due to synchronization, not an increased probability of temporal overlap due an increase in rate-coding.