The relationship between passive stiffness and evoked twitch properties: the influence of muscle CSA normalization

Sex differences in stretch-induced hypertrophy, maximal strength and flexibility gains

Introduction: If the aim is to increase maximal strength (MSt) and muscle mass, resistance training (RT) is primarily used to achieve these outcomes. However, research indicates that long-duration stretching sessions of up to 2 h per day can also provide sufficient stimuli to induce muscle growth. In RT literature, sex-related differences in adaptations are widely discussed, however, there is a lack of evidence addressing the sex-related effects on MSt and muscle thickness (MTh) of longer duration stretch training. Therefore, this study aimed to investigate the effects of 6 weeks of daily (1 h) unilateral static stretch training of the plantar flexors using a calf-muscle stretching device. Methods: Fifty-five healthy (m = 28, f = 27), active participants joined the study. MSt and range of motion (ROM) were measured with extended and flexed knee joint, and MTh was investigated in the medial and lateral heads of the gastrocnemius. Results: Statistically significant increases in MSt of 6%-15% (p < .001-.049, d = 0.45-1.09), ROM of 6%-21% (p < .001-.037, d = 0.47-1.38) and MTh of 4%-14% (p < .001-.005, d = 0.46-0.72) from pre-to post-test were observed, considering both sexes and both legs. Furthermore, there was a significant higher increase in MSt, MTh and ROM in male participants. In both groups, participants showed more pronounced adaptations in MSt and ROM with an extended knee joint as well as MTh in the medial head of the gastrocnemius (p < .001-.047). Results for relative MSt increases showed a similar result (p < .001-.036, d = 0.48-1.03). Discussion: Results are in accordance with previous studies pointing out significant increases of MSt, MTh and ROM due to long duration static stretch training. Both sexes showed significant increases in listed parameters however, male participants showed superior increases.

Development and Clinical Evaluation of a Novel Foot Stretching Robot that Simultaneously Stretches Plantar Fascia and Achilles Tendon for Treatment of Plantar Fasciitis

OBJECTIVE

This paper presents the development and clinical evaluation of a foot stretching robot that simultaneously stretches the plantar fascia and Achilles tendon for the treatment of plantar fasciitis. The therapeutic effectiveness of the robot and feasibility of using metatarsophalangeal joint stiffness as an indicator of recovery were identified through the clinical evaluations.

METHODS

The robot implements an effective foot stretching protocol through a novel mechanism design that simultaneously stretches the plantar fascia and Achilles tendon using a single motor. Thirty patients with plantar fasciitis and fifteen healthy participants volunteered in the cross-sectional clinical evaluation, and nine patients from the patients group participated in the one-month clinical trial. Four main outcomes (Foot Function Index, Visual Analogue Scale-Foot and Ankle, plantar fascia thickness, and metatarsophalangeal joint stiffness) were used for the clinical evaluations.

RESULTS

In the cross-sectional clinical evaluation, the symptomatic feet of patients showed moderate negative correlation between normalized metatarsophalangeal joint stiffness and plantar fascia thickness with statistical significance. In the one-month clinical trial, all the main outcomes showed significant improvement after using the developed robot. Comparing our results with previous studies also indicated a therapeutic superiority of our robot for treating plantar fasciitis.

CONCLUSION

Our foot stretching robot had significant therapeutic effect on plantar fasciitis, and normalized metatarsophalangeal joint stiffness measured by our robot could be used as a monitoring indicator for recovery from plantar fasciitis.

SIGNIFICANCE

This study contributed to practical issues related to treatment of plantar fasciitis, and our results could be applied to effective treatment of plantar fasciitis and progressive monitoring of recovery.

Sex differences in stretch-induced hypertrophy, maximal strength and flexibility gains

Introduction: If the aim is to increase maximal strength (MSt) and muscle mass, resistance training (RT) is primarily used to achieve these outcomes. However, research indicates that long-duration stretching sessions of up to 2 h per day can also provide sufficient stimuli to induce muscle growth. In RT literature, sex-related differences in adaptations are widely discussed, however, there is a lack of evidence addressing the sex-related effects on MSt and muscle thickness (MTh) of longer duration stretch training. Therefore, this study aimed to investigate the effects of 6 weeks of daily (1 h) unilateral static stretch training of the plantar flexors using a calf-muscle stretching device. Methods: Fifty-five healthy (m = 28, f = 27), active participants joined the study. MSt and range of motion (ROM) were measured with extended and flexed knee joint, and MTh was investigated in the medial and lateral heads of the gastrocnemius. Results: Statistically significant increases in MSt of 6%-15% (p < .001-.049, d = 0.45-1.09), ROM of 6%-21% (p < .001-.037, d = 0.47-1.38) and MTh of 4%-14% (p < .001-.005, d = 0.46-0.72) from pre-to post-test were observed, considering both sexes and both legs. Furthermore, there was a significant higher increase in MSt, MTh and ROM in male participants. In both groups, participants showed more pronounced adaptations in MSt and ROM with an extended knee joint as well as MTh in the medial head of the gastrocnemius (p < .001-.047). Results for relative MSt increases showed a similar result (p < .001-.036, d = 0.48-1.03). Discussion: Results are in accordance with previous studies pointing out significant increases of MSt, MTh and ROM due to long duration static stretch training. Both sexes showed significant increases in listed parameters however, male participants showed superior increases.

Electrically Evoked Torque at Rest is Strongly Related to Quadriceps Muscle Size in Individuals with Anterior Cruciate Ligament Reconstruction

Electrically evoked torque at rest (i.e., the torque produced from supramaximal stimul applied to a resting muscle) has been shown to be related to muscle size in healthy adults, but this relationship has not been evaluated in pathological populations where atrophy is present. This study aimed to evaluate the relationship between the electrically evoked torque at rest and vastus lateralis cross-sectional area (CSA) in individuals with anterior cruciate ligament (ACL) reconstruction. Eighteen individuals with ACL reconstruction participated. Quadriceps electrically evoked torque at rest was elicited bilaterally via sex-specific, standardized supramaximal triplet stimulations. Vastus lateralis CSA was measured at 50% of thigh length using ultrasound. Pearson's r and partial correlations were used to evaluate associations between outcomes. Evoked torque at rest was positively associated with vastus lateralis CSA in the ACL reconstructed limb (r=0.865, partial r=0.816, P<0.01), non-reconstructed limb (r=0.628, partial r=0.575, P<0.05), and side-to-side ratios (r=0.670, partial r=0.659, P<0.01). These results indicate that electrically evoked torque at rest may indirectly assess side-to-side differences in quadriceps muscle size after ACL reconstruction.

Acute Effects of Constant-Angle and Constant-Torque Static Stretching on Passive Stiffness of the Posterior Hip and Thigh Muscles in Healthy, Young and Old Men

Palmer, TB. Acute effects of constant-angle and constant-torque static stretching on passive stiffness of the posterior hip and thigh muscles in healthy, young and old men. J Strength Cond Res 33(11): 2991-2999, 2019-The purpose of this study was to examine the acute effects of constant-angle (CA) and constant-torque (CT) static stretching on passive stiffness of the posterior hip and thigh muscles in healthy, young and old men. Fifteen young (25 ± 3 years) and 15 old (71 ± 4 years) men underwent 2 passive straight-leg raise (SLR) assessments before and after 8 minutes of CA and CT stretching using an isokinetic dynamometer. Passive stiffness was calculated during each SLR as the slope of the final 10% of the angle-torque curve. The results indicated that passive stiffness decreased from pre- to post-stretching for both treatments (p ≤ 0.001-0.002) and age groups (p ≤ 0.001-0.046); however, greater decreases were observed for the CT than the CA stretching (p = 0.045) and for the old than the young men (p < 0.001). In addition, baseline stiffness was greater for the old than the younger men (p = 0.010) and was also negatively related (r = -0.721; p < 0.001) to the changes in stiffness from pre- to post-stretching. These findings suggest that holding stretches at a constant tension may be a more effective strategy for altering passive stiffness of the posterior hip and thigh muscles. The greater stretch-induced stiffness decreases observed for the older men provide support that acute static stretching may be particularly effective for reducing stiffness in the elderly. As a result, it may be advantageous to prescribe static stretching before exercise for older adults, as this may be used to elicit substantial declines in passive stiffness, which could help reduce the risk of subsequent injury events in this population.

Is there an intermuscular relationship in voluntary activation capacities and contractile kinetics?

PURPOSE

The force-generating capacities of human skeletal muscles are interrelated, highlighting a common construct of limb strength. This study aimed to further determine whether there is an intermuscular relationship in maximal voluntary activation capacities and contractile kinetics of human muscles.

METHODS

Twenty-six young healthy individuals participated in this study. Isometric maximal voluntary contraction (MVC) torque, voluntary activation level (VAL), and doublet twitch contractile kinetics (contraction time and half-relaxation time) evoked by a paired supramaximal peripheral nerve stimulation at 100 Hz were obtained in elbow flexors, knee extensors, plantar flexors and dorsiflexors of the dominant limb.

RESULTS

Peak MVC torque had significant positive correlations between all muscle group pairs (all P values < 0.01). A significant positive correlation for VAL was found only between knee extensors and plantar flexors (r = 0.60, P < 0.01). There were no significant correlations between all muscle group pairs for doublet twitch contraction time and doublet twitch half-relaxation time.

DISCUSSION

These results show that there is a partial common construct of maximal voluntary activation capacities that only concerns muscle groups that have incomplete activation during MVC (i.e., knee extensors and plantar flexors). This suggests that the common construct of MVC strength between these two muscle groups is partly influenced by neural mechanisms. The lack of intermuscular relationship of contractile kinetics showed that there is no common construct of muscle contractile kinetics, as assessed in vivo by investigating the time-course of evoked doublet twitch contractions.

Effects of Eccentric Preloading on Concentric Vertical Jump Performance in Youth Athletes

This study measured peak force (PF), peak rate of force development (PRFD), peak power (PP), concentric impulse, and eccentric impulse during static jump (SJ), countermovement jump (CMJ), and drop jump (DJ) in youth athletes to examine changes in vertical jump power with progressively greater eccentric preloading in relation to age, maturity, and muscle mass. Twenty-one males ranging from 6 to 16 years old performed the following vertical jumps in a random order: SJ, CMJ, and DJ from drop heights of 20, 30, and 40 cm (DJ20, DJ30, and DJ40, respectively). Measurements included PF, PRFD, PP, eccentric impulse, and concentric impulse for each vertical jump condition. Maturity offset was calculated, while ultrasound images quantified thigh muscle cross-sectional area (CSA). PF and PRFD increased from CMJ to DJ20. PP increased from SJ to CMJ. Concentric impulse remained unchanged, but eccentric impulse increased systematically from across jumps. The change in PP from SJ to CMJ was correlated with age, height, weight, maturity offset, and CSA. The CMJ resulted in the greatest concentric PP with the least amount of eccentric preloading. The inability of young athletes to translate the energy absorbed during the eccentric phase of the stretch-shortening cycle of DJs may be influenced by growth and development.

Muscle strength, size, and neuromuscular function before and during adolescence

PURPOSE

To compare measurements of muscle strength, size, and neuromuscular function among pre-adolescent and adolescent boys and girls with distinctly different strength capabilities.

METHODS

Fifteen boys (mean age ± confidence interval: 13.0 ± 1.0 years) and 13 girls (12.9 ± 1.1 years) were categorized as low strength (LS, n = 14) or high strength (HS, n = 14) based on isometric maximal voluntary contraction strength of the leg extensors. Height (HT), seated height, and weight (WT) determined maturity offset, while percent body fat and fat-free mass (FFM) were estimated from skinfold measurements. Quadriceps femoris muscle cross-sectional area (CSA) was assessed from ultrasound images. Isometric ramp contractions of the leg extensors were performed while surface electromyographic amplitude (EMG_RMS) and mechanomyographic amplitude (MMG_RMS) were recorded for the vastus lateralis (VL). Neuromuscular efficiency from the EMG and MMG signals (NME_EMG and NME_MMG, respectively) and log-transformed EMG and MMG vs. torque relationships were also used to examine neuromuscular responses.

RESULTS

HS was 99-117% stronger, 2.3-2.8  years older, 14.0-15.7 cm taller, 20.9-22.3 kg heavier, 2.3-2.4 years more biologically mature, and exhibited 39-43% greater CSA than LS (p ≤ 0.001). HS exhibited 74-81% higher NME_EMG than LS (p ≤ 0.022), while HS girls exhibited the highest NME_MMG (p ≤ 0.045). Even after scaling for HT, WT, CSA, and FFM, strength was still 36-90% greater for HS than LS (p ≤ 0.031). The MMG_RMS patterns in the LS group displayed more type I motor unit characteristics.

CONCLUSIONS

Neuromuscular adaptations likely influence strength increases from pre-adolescence to adolescence, particularly when examining large, force-producing muscles and large strength differences explained by biological maturity, rather than simply age.

Modified step aerobics training and neuromuscular function in osteoporotic patients: a randomized controlled pilot study

BACKGROUND

Training programs directed to improve neuromuscular and musculoskeletal function of the legs are scarce with respect to older osteoporotic patients. We hypothesized that a modified step aerobics training program might be suitable for this purpose and performed a randomized controlled pilot study to assess the feasibility of conducting a large study. Here we report on the training-related effects on neuromuscular function of the plantar flexors.

PATIENTS AND METHODS

Twenty-seven patients with an age of at least 65 years were enrolled and randomized into control and intervention group. The latter received supervised modified step aerobics training (twice weekly, 1 h per session) over a period of 6 months. At baseline, and after 3 and 6 months neuromuscular function of the plantar flexors, i.e., isometric maximum voluntary torque, rate of torque development and twitch torque parameters were determined in detail in all patients of both groups.

RESULTS

Twenty-seven patients (median age 75 years; range 66-84 years) were randomized (control group n = 14; intervention group n = 13). After 3 and 6 months of training, maximum voluntary contraction strength in the intervention group was significantly higher by 7.7 Nm (9.1%; 95% CI 3.3-12.2 Nm, P < 0.01) and 12.4 Nm (14.8%; 95% CI 6.4-18.5 Nm, P < 0.01) compared to controls. These changes were most probably due to neural and muscular adaptations.

CONCLUSION

It is worthwhile to investigate efficacy of this training program in a large randomized trial. However, a detailed neuromuscular assessment appears feasible only in a subset of participants.

Relationship between muscle volume and contractile properties of the human knee extensors

The present study was designed to investigate the relationship between volume and electrically evoked twitch properties of the quadriceps muscle. Supramaximal single and doublet stimulation of the femoral nerve was used to assess contractile properties at 45° and 80° knee flexion. Muscle volume was measured using a 1.5-Tesla magnetic resonance imaging scanner. Quadriceps muscle volume was only significantly correlated (r = 0.629) with peak twitch torque induced by doublet stimulation at 80° but not at 45° knee flexion.

Comparing passive angle-torque curves recorded simultaneously with a load cell versus an isokinetic dynamometer during dorsiflexion stretch tolerance assessments

The purpose of the present study was to compare the passive angle-torque curves and the passive stiffness (PS, N m °(-)(1)) values recorded simultaneously from a load cell versus an isokinetic dynamometer during dorsiflexion stretch tolerance assessments in vivo. Nine healthy men (mean ± SD age = 21.4 ± 1.6 years) completed stretch tolerance assessments on a custom-built apparatus where passive torque was measured simultaneously from an isokinetic dynamometer and a load cell. Passive torque values that corresponded with the last 10° of dorsiflexion, verified by surface electromyographic amplitude, were analyzed for each device (θ1, θ2, θ3, …, θ10). Passive torque values measured with the load cell were greater (p ≤ 0.05) than the dynamometer torque values for θ4 through θ10. There were more statistical differentiations among joint angles for passive torque measured by the load cell, and the load cell measured a greater (p ≤ 0.01) increase in passive torque and PS than the isokinetic dynamometer. These findings suggested that when examining the angle-torque curves from passive dorsiflexion stretch tolerance tests, a load cell placed under the distal end of the foot may be more sensitive than the torque recorded from an isokinetic dynamometer.

Stretch-induced changes in tension generation process and stiffness are not accompanied by alterations in muscle architecture of the middle and distal portions of the two gastrocnemii

The study aimed to evaluate the stretch-induced changes in muscle architecture in different portions of the gastrocnemius medialis (GM) and lateralis (GL) muscles. The reliability and sensitivity of the measurements were also assessed. Fascicle length (FL) and pennation angle (PA) were calculated in the middle and distal portions of GM and GL at 0°, 10° and 20° of ankle dorsiflexion. At the same angles, passive torque (Tpass), peak torque (pT) and myotendinous junction displacement of GM were determined. Stiffness was calculated at muscle-tendon unit (MTU), muscle and tendon level. After static stretching administration, Tpass, pT and MTU stiffness decreased by 22%, 12% and 16%, respectively (p<0.05). Muscle and tendon stiffness decreased by 15% and 16% (p<0.05). Nevertheless, no changes in FL and PA occurred. The reliability of the approach was always very high (intraclass correlation coefficient>0.90), with an adequate level of sensitivity. pT after static stretching was related to decreases in MTU, muscle and tendon stiffness, but not to alterations in muscle architecture.

Dorsiflexion, plantar-flexion, and neutral ankle positions during passive resistance assessments of the posterior hip and thigh muscles

CONTEXT

Passive straight-legged-raise (SLR) assessments have been performed with the ankle fixed in dorsiflexion (DF), plantar-flexion (PF), or neutral (NTRL) position. However, it is unclear whether ankle position contributes to differences in the passive resistance measured during an SLR assessment.

OBJECTIVE

To examine the influence of ankle position during an SLR on the passive torque, range of motion (ROM), and hamstrings electromyographic (EMG) responses to passive stretch of the posterior hip and thigh muscles.

DESIGN

Crossover study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

A total of 13 healthy volunteers (5 men: age = 24 ± 3 years, height = 178 ± 6 cm, mass = 85 ± 10 kg; 8 women: age = 21 ± 1 years, height = 163 ± 8 cm, mass = 60 ± 6 kg).

INTERVENTION(S)

Participants performed 6 randomly ordered passive SLR assessments involving 2 assessments at each condition, which included the ankle positioned in DF, PF, and NTRL. All SLRs were performed using an isokinetic dynamometer programmed in passive mode to move the limb toward the head at 5°/s.

MAIN OUTCOME MEASURE(S)

During each SLR, maximal ROM was determined as the point of discomfort but not pain, as indicated by the participant. Passive torque and EMG amplitude were determined at 4 common joint angles (θ) separated by 5° during the final common 15° of ROM for each participant.

RESULTS

Passive torque was greater for the DF condition than the NTRL (P = .008) and PF (P = .03) conditions at θ3 and greater for the DF than NTRL condition (P = .02) at θ4. Maximal ROM was lower for the DF condition than the NTRL (P = .003) and PF (P < .001) conditions. However, we found no differences among conditions for EMG amplitude (P = .86).

CONCLUSIONS

These findings suggest that performing SLRs with the ankle positioned in DF may elicit greater passive torque and lower ROM than SLRs with the ankle positioned in PF or NTRL. The greater passive torque and lower ROM induced by the DF condition possibly were due to increased tension in the neural structures of the proximal thigh.

Finite element based nonlinear normalization of human lumbar intervertebral disc stiffness to account for its morphology

Disc degeneration, usually associated with low back pain and changes of intervertebral stiffness, represents a major health issue. As the intervertebral disc (IVD) morphology influences its stiffness, the link between mechanical properties and degenerative grade is partially lost without an efficient normalization of the stiffness with respect to the morphology. Moreover, although the behavior of soft tissues is highly nonlinear, only linear normalization protocols have been defined so far for the disc stiffness. Thus, the aim of this work is to propose a nonlinear normalization based on finite elements (FE) simulations and evaluate its impact on the stiffness of human anatomical specimens of lumbar IVD. First, a parameter study involving simulations of biomechanical tests (compression, flexion/extension, bilateral torsion and bending) on 20 FE models of IVDs with various dimensions was carried out to evaluate the effect of the disc's geometry on its compliance and establish stiffness/morphology relations necessary to the nonlinear normalization. The computed stiffness was then normalized by height (H), cross-sectional area (CSA), polar moment of inertia (J) or moments of inertia (Ixx, Iyy) to quantify the effect of both linear and nonlinear normalizations. In the second part of the study, T1-weighted MRI images were acquired to determine H, CSA, J, Ixx and Iyy of 14 human lumbar IVDs. Based on the measured morphology and pre-established relation with stiffness, linear and nonlinear normalization routines were then applied to the compliance of the specimens for each quasi-static biomechanical test. The variability of the stiffness prior to and after normalization was assessed via coefficient of variation (CV). The FE study confirmed that larger and thinner IVDs were stiffer while the normalization strongly attenuated the effect of the disc geometry on its stiffness. Yet, notwithstanding the results of the FE study, the experimental stiffness showed consistently higher CV after normalization. Assuming that geometry and material properties affect the mechanical response, they can also compensate for one another. Therefore, the larger CV after normalization can be interpreted as a strong variability of the material properties, previously hidden by the geometry's own influence. In conclusion, a new normalization protocol for the intervertebral disc stiffness in compression, flexion, extension, bilateral torsion and bending was proposed, with the possible use of MRI and FE to acquire the discs' anatomy and determine the nonlinear relations between stiffness and morphology. Such protocol may be useful to relate the disc's mechanical properties to its degree of degeneration.

The influence of age on the viscoelastic stretch response

Passive stretching is commonly recommended to help reduce passive stiffness in older adults, yet their acute viscoelastic stretch responses are still unclear. The purpose of this study was to determine the influence of age on the acute viscoelastic responses to a practical stretching intervention. Twenty-two younger (24 ± 3 years) and 14 older (67 ± 3 years) males performed four 30-second passive stretches of the plantar flexors at a predetermined torque threshold. The absolute and relative change in stress relaxation (decline in torque during each 30-second stretch) and creep (increase in ankle joint angle across the 4 stretches) were recorded. Passive stiffness was calculated as the slope of the angle-torque curve at 10° angle of dorsiflexion. There were no differences for the absolute stress relaxation responses (p ≥ 0.118); however, the relative change in stress relaxation was greater (p = 0.010) for the younger vs. older men at stretch 1 (13.0 vs. 8.6%) and decreased across stretches for the younger men (stretch 1 > 3 and 4; p ≤ 0.018), whereas the older men demonstrated a similar relative change across all 4 stretches (p = 0.917). No age related differences were found for either the absolute or relative creep responses (p ≥ 0.072). Passive stiffness was also greater in the older men (p = 0.044). These results suggest that the younger men displayed a greater initial relative stress relaxation response that diminished across the repeated stretches, whereas the older men experienced a smaller relative response that remained constant across the four 30-second stretches. However, the increase in range of motion for a given stretch torque (creep) across all 4 stretches was similar between groups despite differences in passive stiffness.

Associations between lower extremity muscle mass and multiplanar knee laxity and stiffness: a potential explanation for sex differences in frontal and transverse plane knee laxity

BACKGROUND

Compared with men, women have disproportionally greater frontal (varus-valgus) and transverse (internal-external) plane laxity and lower stiffness, despite having similar sagittal (anterior-posterior) plane laxity and stiffness. While the underlying cause is unclear, the amount of lower extremity lean mass (LELM) may be a contributing factor.

HYPOTHESIS

Lower extremity lean mass would be a stronger predictor of frontal and transverse plane laxity and incremental stiffness than the sagittal plane. Associations between LELM and stiffness would be stronger at lower force increments.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Sixty-three women and 30 men with no history of ligament injury were measured for knee laxity and incremental stiffness in the sagittal (-90- to 130-N posterior-to-anterior directed loads), frontal (±10-N·m varus-valgus torques), and transverse (±5-N·m internal-external rotation torques) planes and underwent dual-energy X-ray absorptiometry scans to measure LELM. Linear regressions examined the extent to which LELM predicted each laxity and stiffness value, while also accounting for a person's sex.

RESULTS

Females (vs males) had greater laxity and less stiffness in the frontal and transverse planes but not the sagittal plane. Lower extremity lean mass was a poor predictor of sagittal laxity and stiffness (R (2) range = .021-.081; P > .06) but was a stronger predictor of frontal (R (2) range = .215-.567; P < .01) and transverse (R (2) range = .224-.356; P < .01) plane laxity and stiffness. Associations were stronger for low (R (2) = .495-.504) versus high (R (2) = .215-.435) frontal plane stiffness but were similar for low (R (2) = .233-.293) versus high (R (2) = .224-.356) transverse plane stiffness. Once we accounted for a person's LELM, sex had little effect on laxity and stiffness (change in R (2) after removal = .01-.08; P = .027-.797).

CONCLUSION

Less LELM was associated with greater laxity and less stiffness in frontal and transverse planes, which may contribute to the disproportionally higher laxities and reduced stiffnesses observed in females in these planes.

CLINICAL RELEVANCE

Frontal and transverse plane laxity and stiffness may be modifiable through strength training interventions that promote changes in muscle characteristics (eg, muscle cross-sectional area, stiffness) that may contribute to static knee joint stability, thus dynamic joint stability during sport activity.