The mechanical loading of the spine in physical activities.

PURPOSE: To summarize the mechanical loading of the spine in different activities of daily living and sports. METHODS: Since the direct measurement is not feasible in sports activities, a mathematical model was applied to quantify spinal loading of more than 600 physical tasks in more than 200 athletes from several sports disciplines. The outcome is compression and torque (normalized to body weight/mass) at L4/L5. RESULTS: The data demonstrate high compressive forces on the lumbar spine in sport-related activities, which are much higher than forces reported in normal daily activities and work tasks. Especially ballistic jumping and landing skills yield high estimated compression at L4/L5 of more than ten times body weight. Jumping, landing, heavy lifting and weight training in sports demonstrate compression forces significantly higher than guideline recommendations for working tasks. CONCLUSION: These results may help to identify acute and long-term risks of low back pain and, thus, may guide the development of preventive interventions for low back pain or injury in athletes.

Surface Stiffness and Footwear Affect the Loading Stimulus for Lower Extremity Muscles When Running.

ABSTRACT: Willwacher, S, Fischer, KM, Rohr, E, Trudeau, MB, Hamill, J, and Brüggemann, G-P. Surface stiffness and footwear affect the loading stimulus for lower extremity muscles when running. J Strength Cond Res 36(1): 82-89, 2022-Running in minimal footwear or barefoot can improve foot muscle strength. Muscles spanning the foot and ankle joints have the potential to improve performance and to reduce overuse injury risk. Surface stiffness or footwear use could modify the intensity of training stimuli acting on lower extremity joints during running. The purpose of this study was to systematically investigate external ankle, knee, and hip joint moments during shod and barefoot running while considering the stiffness of the running surface. Two footwear conditions (barefoot and neutral running shoe) and 4 surface conditions (Tartan, Tartan + Ethylene Vinyl Acetate [EVA] foam, Tartan + artificial turf, Tartan + EVA foam + artificial turf) were tested at 3.5 m·s-1. Repeated measures analysis of variance revealed that barefoot running in general and running barefoot on harder surfaces increased and decreased ankle (between +5 and +26%) and knee (between 0 and -11%) joint moments, respectively. Averaged over all surfaces, running barefoot was characterized by a 6.8° more plantarflexed foot strike pattern compared with running shod. Foot strike patterns were more plantarflexed on harder surfaces; the effects, however, were less than 3°. Most surface effects were stronger in barefoot compared with shod running. Surface stiffness may be used to modulate the loading intensity of lower extremity muscles (in particular extrinsic and intrinsic foot muscles) during running. These results need to be considered when coaches advise barefoot running as a method to improve the strength of extrinsic and intrinsic foot muscles or when trying to reduce knee joint loading.

Nordic Hamstring Exercise training induces improved lower-limb swing phase mechanics and sustained strength preservation in sprinters.

Nordic Hamstring Exercise (NHE) training improves eccentric hamstring strength and sprint performance. However, detraining causes rapid reductions of achieved adaptations. Furthermore, the transfer of improved hamstring capacity to swing phase mechanics of sprints is unknown. This longitudinal study aimed (a) to quantify NHE-induced adaptations by camera-based isokinetic assessments and sprint analyses, (b) to relate the magnitude of adaptations to the participants' initial performance level, (c) to investigate the transferability to sprints, and (4) to determine strength preservations after 3 months. Twelve sprinters (21 years, 1.81 m, 74 kg) were analyzed throughout 22 weeks. They performed maximal sprints and eccentric knee flexor and concentric knee extensor tests before and after a 4-week NHE training. Sprints and isokinetic tests were captured by ten and four high-speed cameras. The dynamic control ratio at the equilibrium point (DCRe) evaluated thigh muscle balance. High-intensity NHE training elicited significant improvements of hamstring function (P range: <.001-.011, d range: 0.44-1.14), thigh muscle balance (P < 0.001, d range: 0.80-1.08) and hamstring-related parameters of swing phase mechanics (P range: <0.001-0.022, d range: 0.12-0.57). Sprint velocity demonstrated small increases (+1.4%, P < 0.001, d = 0.26). Adaptations of hamstring function and thigh muscle balance revealed moderate to strong transfers to improved sprint mechanics (P range: <0.001-0.048, R2 range: 34%-83%). The weakest participants demonstrated the highest adaptations of isokinetic parameters (P range: 0.003-0.023, R2 range: 42%-62%), whereas sprint mechanics showed no effect of initial performance level. Three months after the intervention, hamstring function (+6% to +14%) and thigh muscle balance (+8% to +10%) remained significantly enhanced (P < 0.001, ƞp 2 range: 0.529-0.621). High-intensity NHE training induced sustained improved hamstring function of sprinters, which can be transferred to swing phase mechanics of maximal sprints. The initial performance level, NHE training procedures and periodization should be considered to optimize adaptations.

Spinal and Pelvic Kinematics During Prolonged Rowing on an Ergometer vs. Indoor Tank Rowing.

ABSTRACT: Trompeter, K, Weerts, J, Fett, D, Firouzabadi, A, Heinrich, K, Schmidt, H, Brüggemann, GP, and Platen, P. Spinal and pelvic kinematics during prolonged rowing on an ergometer vs. indoor tank rowing. J Strength Cond Res 35(9): 2622-2628, 2021-This investigation aimed to compare spinopelvic kinematics during rowing on an ergometer vs. in a rowing tank and to evaluate changes with progressing fatigue. Spinal and pelvic kinematics of 8 competitive scull rowers (19.0 ± 2.1 years, 179.9 ± 7.6 cm, and 74.8 ± 8.1 kg) were collected during 1 hour of rowing on an ergometer and in a rowing tank using a routine training protocol. Kinematics of the upper thoracic spine, lower thoracic spine, lumbar spine, and pelvis were determined using an infrared camera system (Vicon, Oxford, United Kingdom). There was a greater lumbar range of motion (ROM) and less posterior pelvic tilt at the catch during rowing on the ergometer compared with in the rowing tank (p = 0.001-0.048), but no differences in pelvic ROM. In the rowing tank, the pelvic ROM increased over time (p = 0.002) and the ROM of the lower thoracic spine decreased (p = 0.002). In addition, there was an extended drive phase (when the rower applies pressure to the oar levering the boat forward) and an abbreviated recovery phase (setting up the rower's body for the next stroke) in the rowing tank (p = 0.032). Different rowing training methods lead to differences in spinopelvic kinematics, which may lead to substantially different spinal loading situations. Greater pelvic rotation and lesser lumbar ROM are considered ideal; therefore, the present results indicate that rowing in the rowing tank might facilitate the maintenance of this targeted spinopelvic posture, which might help protect the lower back. Rowers, coaches, and researchers should consider the differences between rowing training methods, especially when giving training recommendations.

Does footwear affect articular cartilage volume change after a prolonged run?

The aim of this study was to investigate knee intra-articular cartilage volume changes after a prolonged running bout in three footwear conditions. Twelve participants performed 75-minute running bouts in the three footwear conditions. Before and after each running bout, magnetic resonance imaging (MRI) scans were obtained using a high-resolution 3.0 Tesla MRI. Three-dimensional reconstruction of the cartilage plates of the patella, the femur, and the tibia was created to quantify cartilage volume change due to the 75-minute running bout. Three-dimensional biomechanical data were also collected using an integrated motion capture and force treadmill system. There were no statistically significant differences among shoe conditions for all anatomical regions. However, significant cartilage volume reductions at all anatomical sites were observed after the 75-minute running bout in each footwear condition. These data suggest that the intra-articular knee cartilage undergoes a significant reduction in cartilage volume during a prolonged run that may indicate an increase in joint loading. There was a considerable variation in cartilage volume between participants across footwear conditions indicating an individual cartilage volume response to footwear. An individualistic approach to footwear recommendations may help in minimizing this change in cartilage.

Calcaneal adduction and eversion are coupled to talus and tibial rotation.

The purpose of this study was to quantify isolated coupling mechanisms of calcaneal adduction/abduction and calcaneal eversion/inversion to proximal bones in vitro. The in vitro approach is necessary because in vivo both movements appear together, making it impossible to determine the extent of their individual contribution to overall ankle joint coupling. Eight fresh frozen foot-leg specimens were tested. Data describing bone orientation and coupling mechanisms between segments were obtained using bone pin marker triads. The bone movement was described in a global coordinate system to examine the coupling between the calcaneus, talus and tibia. The strength of coupling was determined by means of the slope of a linear least squares fit to an angle-angle plot. The coupling coefficients in the present study indicate that not only calcaneal eversion/inversion (coupling coefficient: 0.68 ± 0.15) but to an even greater extent calcaneal adduction/abduction (coupling coefficient: 0.99 ± 0.10) was transferred into talus and tibial rotation, highlighting the relevance of calcaneal adduction for the overall ankle joint coupling. The results of this study present the possibility that controlling calcaneal adduction/abduction can affect talus and tibial rotation and therefore the possible genesis of overuse knee injuries.

The Achilles tendon is mechanosensitive in older adults: adaptations following 14†weeks versus 1.5†years of cyclic strain exercise.

The aging musculoskeletal system experiences a general decline in structure and function, characterized by a reduced adaptability to environmental stress. We investigated whether the older human Achilles tendon (AT) demonstrates mechanosensitivity (via biomechanical and morphological adaptations) in response to long-term mechanical loading. Thirty-four female adults (60-75 years) were allocated to either a medium-term (14 weeks; N=21) high AT strain cyclic loading exercise intervention or a control group (N=13), with 12 participants continuing with the intervention for 1.5 years. AT biomechanical properties were assessed using ultrasonography and dynamometry. Tendon cross-sectional area (CSA) was investigated by means of magnetic resonance imaging. A 22% exercise-related increment in ankle plantarflexion joint moment, along with increased AT stiffness (598.2±141.2 versus 488.4±136.9 N mm-1 at baseline), Young's modulus (1.63±0.46 versus 1.37±0.39 GPa at baseline) and about 6% hypertrophy along the entire free AT were identified after 14 weeks of strength training, with no further improvement after 1.5 years of intervention. The aging AT appears to be capable of increasing its stiffness in response to 14 weeks of mechanical loading exercise by changing both its material and dimensional properties. Continuing exercise seems to maintain, but not cause further adaptive changes in tendons, suggesting that the adaptive time-response relationship of aging tendons subjected to mechanical loading is nonlinear.

Aqua Cycling Does Not Affect Recovery of Performance, Damage Markers, and Sensation of Pain.

Wahl, P, Sanno, M, Ellenberg, K, Frick, H, Böhm, E, Haiduck, B, Goldmann, J-P, Achtzehn, S, Brüggemann, G-P, Mester, J, and Bloch, W. Aqua cycling does not affect recovery of performance, damage markers, and sensation of pain. J Strength Cond Res 31(1): 162-170, 2017-To examine the effects of aqua cycling (AC) vs. passive recovery (P) on performance, markers of muscle damage, delayed onset of muscle soreness (DOMS), and the persons perceived physical state (PEPS) after 300 countermovement jumps (CMJs). Twenty male participants completed 300 CMJs. Afterward, they were randomly assigned to either the P group or the AC group, the latter performing 30 minutes of AC. Before, directly after the 300 CMJs, after the recovery session, and up to 72 hours post, performance of leg extensor muscles, damage markers, the PEPS, and DOMS were measured. Jumping height during 300 CMJs significantly decreased in both groups (AC: 13.4% and P: 14.6%). Maximal isometric strength (AC: 21% and P: 22%) and dynamic fatigue test (AC: 35% and P: 39%) of leg extensor muscles showed significant decreases in both groups. Myoglobin, creatine kinase, and lactate dehydrogenase significantly increased over time in both groups. Each of the 4 dimensions of the PEPS and DOMS showed significant changes over time. However, no significant differences between both groups were found for any of the parameters. Coaches and athletes should be aware that vertical jumping-induced fatigue decreases the ability to generate maximal isometric and submaximal dynamic force for more than 3 days after training. A single 30-minute session of AC was not able to attenuate the effects on muscular performance, markers of muscle damage, DOMS, or the PEPS compared with passive rest.

Associations Between Bipedal Stance Stability and Locomotor Stability Following a Trip in Unilateral Vestibulopathy.

Posturography is used to assess balance in clinical settings, but its relationship to gait stability is unclear. We assessed if dynamic gait stability is associated with standing balance in 12 patients with unilateral vestibulopathy. Participants were unexpectedly tripped during treadmill walking and the change in the margin of stability (MoSchange) and base of support (BoSchange) relative to nonperturbed walking was calculated for the perturbed and first recovery steps. The center of pressure (COP) path during 30-s stance with eyes open and closed, and the distance between the most anterior point of the COP and the anterior BoS boundary during forward leaning (ADist), were assessed using a force plate. Pearson correlations were conducted between the static and dynamic variables. The perturbation caused a large decrease in the BoS, leading to a decrease in MoS. One of 12 correlations was significant (MoSchange at the perturbed step and ADist; r = -.595, P = .041; nonsignificant correlations: .068 ≤ P ≤ .995). The results suggest that different control mechanisms may be involved in stance and gait stability, as a consistent relationship was not found. Therefore, posturography may be of limited use in predicting stability in dynamic situations.

Visual and proprioceptive contributions to postural control of upright stance in unilateral vestibulopathy.

Preserving upright stance requires central integration of the sensory systems and appropriate motor output from the neuromuscular system to keep the centre of pressure (COP) within the base of support. Unilateral peripheral vestibular disorder (UPVD) causes diminished stance stability. The aim of this study was to determine the limits of stability and to examine the contribution of multiple sensory systems to upright standing in UPVD patients and healthy subjects. We hypothesized that closure of the eyes and Achilles tendon vibration during upright stance will augment the postural sway in UPVD patients more than in healthy subjects. Seventeen UPVD patients and 17 healthy subjects performed six tasks on a force plate: forwards and backwards leaning, to determine limits of stability, and upright standing with and without Achilles tendon vibration, each with eyes open and closed (with blackout glasses). The COP displacement of the patients was significantly greater in the vibration tasks than the controls and came closer to the posterior base of support boundary than the controls in all tasks. Achilles tendon vibration led to a distinctly more backward sway in both subject groups. Five of the patients could not complete the eyes closed with vibration task. Due to the greater reduction in stance stability when the proprioceptive, compared with the visual, sensory system was disturbed, we suggest that proprioception may be more important for maintaining upright stance than vision. UPVD patients, in particular, showed more difficulty in controlling postural stability in the posterior direction with visual and proprioceptive sensory disturbance.

Evaluating the potential synergistic benefit of a realignment brace on patients receiving exercise therapy for patellofemoral pain syndrome: a randomized clinical trial.

BACKGROUND: It has been previously shown that exercise programs for patellofemoral pain syndrome (PFPS) can be supported by medially directed taping. Evidence supporting the use of patellar braces is limited because previous studies have been low quality. The aim of this study is to compare the outcomes of patients with PFPS after treatment with a medially directed patellar realignment brace and supervised exercise. METHODS: In a prospective randomized multicenter trial, 156 patients with PFPS were included and randomly assigned to 6 weeks of supervised physiotherapy in combination with the patellar realignment brace, or supervised physiotherapy alone. Outcome measures were the Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales, numeric analog pain scores, and the Kujala score at baseline, 6 weeks, 3 months, and 1 year after the start of therapy. The patient's self-reported perception of recovery was also assessed at these points. RESULTS: Both treatment groups showed a significant improvement in all outcome measures over the study period. After 6 and 12 weeks of therapy, patients in the brace group had significantly higher KOOS sub-scale scores, a higher mean Kujala score, and less pain while climbing stairs or playing sports. After 54 weeks a group difference could be only detected for the KOOS ADL sub-scale. CONCLUSION: The use of a medially directed realignment brace leads to better outcomes in patients with PFPS than exercise alone after 6 and 12 weeks of treatment. After 1 year of follow-up this positive effect diminished.

Moderate cyclic tensile strain alters the assembly of cartilage extracellular matrix proteins in vitro.

Mechanical loading influences the structural and mechanical properties of articular cartilage. The cartilage matrix protein collagen II essentially determines the tensile properties of the tissue and is adapted in response to loading. The collagen II network is stabilized by the collagen II-binding cartilage oligomeric matrix protein (COMP), collagen IX, and matrilin-3. However, the effect of mechanical loading on these extracellular matrix proteins is not yet understood. Therefore, the aim of this study was to investigate if and how chondrocytes assemble the extracellular matrix proteins collagen II, COMP, collagen IX, and matrilin-3 in response to mechanical loading. Primary murine chondrocytes were applied to cyclic tensile strain (6%, 0.5 Hz, 30 min per day at three consecutive days). The localization of collagen II, COMP, collagen IX, and matrilin-3 in loaded and unloaded cells was determined by immunofluorescence staining. The messenger ribo nucleic acid (mRNA) expression levels and synthesis of the proteins were analyzed using reverse transcription-polymerase chain reaction (RT-PCR) and western blots. Immunofluorescence staining demonstrated that the pattern of collagen II distribution was altered by loading. In loaded chondrocytes, collagen II containing fibrils appeared thicker and strongly co-stained for COMP and collagen IX, whereas the collagen network from unloaded cells was more diffuse and showed minor costaining. Further, the applied load led to a higher amount of COMP in the matrix, determined by western blot analysis. Our results show that moderate cyclic tensile strain altered the assembly of the extracellular collagen network. However, changes in protein amount were only observed for COMP, but not for collagen II, collagen IX, or matrilin-3. The data suggest that the adaptation to mechanical loading is not always the result of changes in RNA and/or protein expression but might also be the result of changes in matrix assembly and structure.

Effect of whole-body vibration and insulin-like growth factor-I on muscle paralysis-induced bone degeneration after botulinum toxin injection in mice.

Botulinum toxin A (BTX)-induced muscle paralysis results in pronounced bone degradation with substantial bone loss. We hypothesized that whole-body vibration (WBV) and insulin-like growth factor-I (IGF-I) treatment can counteract paralysis-induced bone degradation following BTX injections by activation of the protein kinase B (Akt) signaling pathway. Female C57BL/6 mice (n = 60, 16 weeks) were assigned into six groups (n = 10 each): SHAM, BTX, BTX+WBV, BTX+IGF-I, BTX+WBV+IGF-I, and a baseline group, which was killed at the beginning of the study. Mice received a BTX (1.0 U/0.1 mL) or saline (SHAM) injection in the right hind limb. The BTX+IGF-I and BTX+WBV+IGF-I groups obtained daily subcutaneous injections of human IGF-I (1 µg/day). The BTX+WBV and BTX+WBV+IGF-I groups underwent WBV (25 Hz, 2.1 g, 0.83 mm) for 30 min/day, 5 days/week for 4 weeks. Femora were scanned by pQCT, and mechanical properties were determined. On tibial sections TRAP staining, static histomorphometry, and immunohistochemical staining against Akt, phospho-Akt, IGF-IR (IGF-I receptor), and phospho-IGF-IR were conducted. BTX injection decreased trabecular and cortical bone mineral density. The WBV and WBV+IGF-I groups showed no difference in trabecular bone mineral density compared to the SHAM group. The phospho-IGF-IR and phospho-Akt stainings were not differentially altered in the injected hind limbs between groups. We found that high-frequency, low-magnitude WBV can counteract paralysis-induced bone loss following BTX injections, while we could not detect any effect of treatment with IGF-I.

The Patella Pro study - effect of a knee brace on patellofemoral pain syndrome: design of a randomized clinical trial (DRKS-ID:DRKS00003291).

BACKGROUND: Patellofemoral pain syndrome (PFPS) is a frequent cause of anterior knee pain predominantly affecting young female patients who do not have significant chondral damage. Development of PFPS is probably multifactorial, involving various knee, hip, and foot kinematic factors. Biomechanical studies have described patellar maltracking and dynamic valgus (functional malalignment) in patients with patellofemoral pain syndrome. The literature provides evidence for short-term use of nonsteroidal anti-inflammatory drugs; short-term medially directed taping; and exercise programs focusing on the lower extremity, hip, and trunk muscles. Evidence supporting the use of patellar braces is limited because previous studies have been low quality. The aim of this article is to publish the design of a prospective randomized trial that examines the outcomes of patients with PFPS after treatment with a new patellar brace (Patella Pro) that applies medially directed force on the patella. METHODS/DESIGN: For this multicenter trial, 156 patients (adolescents and young adults) with PFPS were recruited from orthopedic practices and orthopedic hospitals and randomly allocated to 3 months of supervised physiotherapy in combination with the Patella Pro brace or supervised physiotherapy alone. The primary outcome measures are pain (numerical analog scale); knee function (Kujala score and Knee Injury and Osteoarthritis Outcome Score); and self-reported perception of recovery at baseline, 6 weeks, 3 months, and 1 year. DISCUSSION: Only limited evidence for the use of a patellar brace for the treatment of PFPS exists in the literature. Disputable evidence for the use of orthoses for PFPS patients has been presented in one meta-analysis, in which only one of three studies found the effect of a medially directed patellar brace to be significant. Because of these low-quality studies, the authors concluded that this evidence should be regarded as limited, and we feel there is a need for further well-designed studies to evaluate the effect of patellar bracing on PFPS-related pain. The Patella Pro study is a prospective randomized trial in which supervised physiotherapy in combination with a patellar brace is compared with supervised physiotherapy alone. This trial started in April 2012 and finished in October 2013. TRIAL REGISTRATION: DRKS-ID:DRKS00003291, January 3rd, 2012.

Effect of carpometacarpal joint osteoarthritis, sex, and handedness on thumb in vivo kinematics.

PURPOSE: To investigate the influence of trapeziometacarpal (TMC) osteoarthritis (OA) on the 3-dimensional motion capability of the TMC and thumb metacarpophalangeal (MCP) joints. In order to examine other factors affecting the thumb's motion kinematics, we further aimed to address the influence of sex and handedness on the motion capability of normal TMC and MCP joints. METHODS: We included 18 healthy subjects (9 women, 9 men; 8 dominant hands, 10 nondominant hands) and 18 women with stage II/III TMC OA. A motion analysis system using surface markers was used to quantify the thumb's 3-dimensional opposition-reposition kinematics. The range of motion of the thumb's TMC and MCP joints in flexion-extension, abduction-adduction, and pronation-supination were determined. RESULTS: TMC OA led to a loss in abduction-adduction in the TMC joint (38° in controls, 26° in TMC OA subjects), although neither flexion-extension nor pronation-supination were affected. At the MCP joint, the TMC OA subjects showed a 48% reduction in abduction-adduction (32° controls, 16° TMC OA subjects) and 42% reduction in pronation-supination (34° in controls, 20° in TMC OA subjects) than the healthy controls. Ranges of motion of the healthy TMC and MCP joints were similar in dominant and nondominant hands as well as in women and men. DISCUSSION: The study demonstrated that stage II/III TMC OA restricts the motion of the TMC joint in abduction-adduction and of the MCP joint in abduction-adduction and pronation-supination. Thumb motion capability was unaffected by sex and handedness. CLINICAL RELEVANCE: Osteoarthritis-induced loss of TMC motion did not reflect a generalizable clinical parameter, rather, it seemed to distinctly affect the TMC and the MCP joints and their motion planes and directions. As neither sex nor handedness influenced the motion capabilities of the healthy thumb, kinematic factors contributing to TMC OA may develop at a later age.

Sequence of the Essex-Lopresti lesion--a high-speed video documentation and kinematic analysis.

BACKGROUND AND PURPOSE: The pathomechanics of the Essex-Lopresti lesion are not fully understood. We used human cadavers and documented the genesis of the injury with high-speed cameras. METHODS: 4 formalin-fixed cadaveric specimens of human upper extremities were tested in a prototype, custom-made, drop-weight test bench. An axial high-energy impulse was applied and the development of the lesion was documented with 3 high-speed cameras. RESULTS: The high-speed images showed a transversal movement of the radius and ulna, which moved away from each other in the transversal plane during the impact. This resulted into a transversal rupture of the interosseous membrane, starting in its central portion, and only then did the radius migrate proximally and fracture. The lesion proceeded to the dislocation of the distal radio-ulnar joint and then to a full-blown Essex-Lopresti lesion. INTERPRETATION: Our findings indicate that fracture of the radial head may be preceded by at least partial lesions of the interosseous membrane in the course of high-energy axial trauma.

Growth-related structural, biochemical, and mechanical properties of the functional bone-cartilage unit.

Articular cartilage and subchondral bone act together, forming a unit as a weight-bearing loading-transmitting surface. A close interaction between both structures has been implicated during joint cartilage degeneration, but their coupling during normal growth and development is insufficiently understood. The purpose of the present study was to examine growth-related changes of cartilage mechanical properties and to relate these changes to alterations in cartilage biochemical composition and subchondral bone structure. Tibiae and femora of both hindlimbs from 7- and 13-week-old (each n = 12) female Sprague-Dawley rats were harvested. Samples were processed for structural, biochemical and mechanical analyses. Immunohistochemical staining and protein expression analyses of collagen II, collagen IX, COMP and matrilin-3, histomorphometry of cartilage thickness and COMP staining height were performed. Furthermore, mechanical testing of articular cartilage and micro-CT analysis of subchondral bone was conducted. Growth decreased cartilage thickness, paralleled by a functional condensation of the underlying subchondral bone due to enchondral ossification. Cartilage mechanical properties seem to be rather influenced by growth-related changes in the assembly of major ECM proteins such as collagen II, collagen IX and matrilin-3 than by growth-related alterations in its underlying subchondral bone structure. Importantly, the present study provides a first insight into the growth-related structural, biochemical and mechanical interaction of articular cartilage and subchondral bone. Finally, these data contribute to the general knowledge about the cooperation between the articular cartilage and subchondral bone.

The potential of toe flexor muscles to enhance performance.

The metatarsal phalangeal joint (MPJ) and its crossing toe flexor muscles (TFM) represent the link between the large energy generating leg extensor muscles and the ground. The purpose of this study was to examine the functional adaptability of TFM to increased mechanical stimuli and the effects on walking, running and jumping performance. Fifteen men performed a heavy resistance TFM strength training with 90% of the maximal voluntary isometric contraction (MVIC) for 7 weeks (560 contractions) for the left and right foot. Maximal MPJ and ankle plantar flexion moments during MVICs were measured in dynamometers before and after the intervention. Motion analyses (inverse dynamics) were performed during barefoot walking, running, and vertical and horizontal jumping. Athletic performance was determined by measuring jump height and distance. Left (0.21 to 0.38 Nm · kg(-1); P < 0.001) and right (0.24 to 0.40 Nm · kg(-1); P < 0.001) MPJ plantar flexion moments in the dynamometer, external MPJ dorsiflexion moments (0.69 to 0.75 Nm · kg(-1); P = 0.012) and jump distance (2.25 to 2.31 m; P = 0.006) in horizontal jumping increased significantly. TFM responded highly to increased loading within a few weeks. The increased force potential made a contribution to an athlete's performance enhancement.

Effect of heel construction on muscular control potential of the ankle joint in running.

The purpose of this study was to investigate the effect of heel construction on ankle joint mechanics during the early stance phase of running. Kinematic and kinetic parameters (ankle joint angles, angular velocities and joint moments, lever arms of ground reaction force, triceps surae muscle tendon unit lengths, and rates of muscle tendon unit length change) were calculated from 19 male subjects running at 3.3 m/s in shoes with different heel constructions. Increasing heel height and posterior wedging amplified initial plantar flexion velocity and range. The potential for a muscle to control the movement of a joint depends upon its ability to produce joint moments. Runners in this study showed decreased external eversion moments and an increase in eversion range. Maximum eversion angles were not significantly affected by shoe conditions. Without considerable tendon prestretch, joint moment generation potentials of triceps surae and deep plantar flexors might be inhibited due to rapid plantar flexion based on the force-velocity relationship. It could be speculated that increasing ankle inversion at heel strike could be a strategy to keep maximum eversion angles inside an adequate range, if joint moment generation potentials of deep plantar flexors are inhibited due to rapid plantar flexion.

Does specific footwear facilitate energy storage and return at the metatarsophalangeal joint in running?

Longitudinal midsole bending stiffness and elasticity are two critical features in the construction of running shoes. Stiff elastic materials (eg, carbon fiber) can be used to alter the midsole bending behavior. The purpose of this study was to investigate the effects of midsole stiffness and elasticity manipulation on metatarsophalangeal (MTP) joint mechanics during running in 19 male subjects at 3.5 m/s. Midsole bending stiffness and elasticity were modified by means of carbon fiber insoles of varying thickness. Stiffening the shoe structures around the MTP joint caused a shift of the point of force application toward the front edge of the shoe-ground interface. Negative work was significantly reduced for the stiffest shoe condition and at the same time a significant increase of positive work at the MTP joint was found. It seems plausible that the increase in positive work originates from the reutilization of elastic energy that was stored inside the passive elastic structures of the shoe and toe flexing muscle tendon units. Further, an increase in midsole longitudinal bending stiffness seems to alter the working conditions and mechanical power generation capacities of the MTP plantar flexing muscle tendon units by changing ground reaction force leverage and MTP angular velocity.