Length-tension Relationship Research Articles

Aging-related alterations in eNOS and nNOS responsiveness and smooth muscle reactivity of murine basilar arteries are modulated by apocynin and phosphorylation of myosin phosphatase targeting subunit-1

Aging causes major alterations of all components of the neurovascular unit and compromises brain blood supply. Here, we tested how aging affects vascular reactivity in basilar arteries from young (<10 weeks; y-BA), old (>22 months; o-BA) and old (>22 months) heterozygous MYPT1-T-696A/+ knock-in mice. In isometrically mounted o-BA, media thickness was increased by ∼10% while the passive length tension relations were not altered. Endothelial denudation or pan-NOS inhibition (100 µmol/L L-NAME) increased the basal tone by 11% in y-BA and 23% in o-BA, while inhibition of nNOS (1 µmol/L L-NPA) induced ∼10% increase in both ages. eNOS expression was ∼2-fold higher in o-BA. In o-BA, U46619-induced force was augmented (pEC50 ∼6.9 vs. pEC50 ∼6.5) while responsiveness to DEA-NONOate, electrical field stimulation or nicotine was decreased. Basal phosphorylation of MLC20-S19 and MYPT1-T-853 was higher in o-BA and was reversed by apocynin. Furthermore, permeabilized o-BA showed enhanced Ca2+-sensitivity. Old T-696A/+ BA displayed a reduced phosphorylation of MYPT1-T696 and MLC20, a lower basal tone in response to L-NAME and a reduced eNOS expression. The results indicate that the vascular hypercontractility found in o-BA is mediated by inhibition of MLCP and is partially compensated by an upregulation of endothelial NO release.

Triceps-reflecting anconeus pedicle approach with double precontoured locking plate fixation is efficient in the treatment of orthopaedic trauma association type C distal humerus fracture

BackgroundThe purpose of this study was to determine if the triceps-reflecting anconeus pedicle (TRAP) approach combined with the precontoured locking plate can provide acceptable clinical outcomes in the treatment of comminuted distal humerus fracture. MethodsBetween August 2008 and June 2014, 48 patients with Orthopaedic Trauma Association type C (21 with C2, 27 with C3) distal humerus fractures underwent open reduction and internal fixation with orthogonal precontoured locking plate fixation using the TRAP approach. Occurrences of bony union, implant failure, posttraumatic arthrosis, and heterotopic ossification were detected with radiography. Clinical assessment included evaluation of range of motion and determination of the pain score, Mayo Elbow Performance Index (MEPI) score, and Disability of the Arm Shoulder and Hand (DASH) score. ResultsThe fractures healed within 3 months in 25 patients (53%) and within 6 months in 23 patients (47%). The 12-month assessment revealed improved elbow movement, with the mean arc of flexion-extension of 121° (range, 100°–140°), mean arc of supination-pronation of 163° (range, 150°–180°), and mean flexion contracture of 8° (range, 0°–30°). The mean MEPI score was 81 and the mean DASH score was 11.7. ConclusionsBy retaining the intact olecranon by the TRAP approach, orthopedic surgeon can get adequate surgical exposure for fracture fixation and can use olecranon as a three-dimensional template to restore the articular fragments. The promising results in this study obtain because that precise identification of the triceps muscle allowed the determination of a proper length-tension relationship for triceps reattachment. The combination of triceps tendon repair and anconeous muscle repair ensured the strength of the extensor mechanism. Therefore, the TRAP approach in combination with the usage of the precontoured locking plate can be recommended as the optimal surgical approach for the treatment of comminuted distal humerus fracture.

Arthroscopic knotless suprapectoral tenodesis of the long head of biceps: clinical and structural results.

Different techniques for tenodesis of the long head of biceps (LHB) have been described. Previous studies focused on intraosseously performed techniques while only little clinical data exists for epiosseously performed knotless LHB tenodesis. The hypothesis is that arthroscopic suprapectoral knotless epiosseous tenodesis of the LHB would have good clinical, cosmetic and structural results. Forty-nine patients [16 women, 33 men; mean age 58; mean follow-up 36.4months (range 24-57months)], in whom a tenodesis of the long biceps tendon (LHB) has been performed, were included into this study. The clinical evaluation included the Constant score as well as the LHB score. In addition elbow flexion and supination strength were assessed. The integrity of the tenodesis construct was evaluated indirectly by sonographic detection of the LHB in the bicipital groove. The overall Constant score did not reveal any significant differences comparing both sides [mean, 86±19 points vs. 89±16 points (p>0.05)]. The mean LHB score reached 88.3 points (range 54-100 points). Thirty-four patients (69%) presented an examiner-dependent upper arm deformity although only three patients (6%) confirmed a subjective cosmetic deformity. Both, flexion and supination strength were significantly decreased compared to the non-operated side (p<0.05). In five patients (10%) it was not possible to verify the LHB sonographically in the bicipital groove. Therefore the biceps tenodesis was classified as a failure. The arthroscopic suprapectoral epiosseous knotless tenodesis of the LHB provides good functional results. The high rate of examiner-dependent upper arm deformities can be explained by a non-physiological situation of the primary length-tension relationship or an elongation of the tendon after fixation.

Muscle architectural changes after massive human rotator cuff tear.

Rotator cuff (RC) tendon tears lead to negative structural and functional changes in the associated musculature. The structural features of muscle that predict function are termed "muscle architecture." Although the architectural features of "normal" rotator cuff muscles are known, they are poorly understood in the context of cuff pathology. The purpose of this study was to investigate the effects of tear and repair on RC muscle architecture. To this end thirty cadaveric shoulders were grouped into one of four categories based on tear magnitude: Intact, Full-thickness tear (FTT), Massive tear (MT), or Intervention if sutures or hardware were present, and key parameters of muscle architecture were measured. We found that muscle mass and fiber length decreased proportionally with tear size, with significant differences between all groups. Conversely, sarcomere number was reduced in both FTT and MT with no significant difference between these two groups, in large part because sarcomere length was significantly reduced in MT but not FTT. The loss of muscle mass in FTT is due, in part, to subtraction of serial sarcomeres, which may help preserve sarcomere length. This indicates that function in FTT may be impaired, but there is some remaining mechanical loading to maintain "normal" sarcomere length-tension relationships. However, the changes resulting from MT suggest more severe limitations in force-generating capacity because sarcomere length-tension relationships are no longer normal. The architectural deficits observed in MT muscles may indicate deeper deficiencies in muscle adaptability to length change, which could negatively impact RC function despite successful anatomical repair. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2089-2095, 2016.

Transient contractions of urinary bladder smooth muscle are drivers of afferent nerve activity during filling.

Activation of afferent nerves during urinary bladder (UB) filling conveys the sensation of UB fullness to the central nervous system (CNS). Although this sensory outflow is presumed to reflect graded increases in pressure associated with filling, UBs also exhibit nonvoiding, transient contractions (TCs) that cause small, rapid increases in intravesical pressure. Here, using an ex vivo mouse bladder preparation, we explored the relative contributions of filling pressure and TC-induced pressure transients to sensory nerve stimulation. Continuous UB filling caused an increase in afferent nerve activity composed of a graded increase in baseline activity and activity associated with increases in intravesical pressure produced by TCs. For each ∼4-mmHg pressure increase, filling pressure increased baseline afferent activity by ∼60 action potentials per second. In contrast, a similar pressure elevation induced by a TC evoked an ∼10-fold greater increase in afferent activity. Filling pressure did not affect TC frequency but did increase the TC rate of rise, reflecting a change in the length-tension relationship of detrusor smooth muscle. The frequency of afferent bursts depended on the TC rate of rise and peaked before maximum pressure. Inhibition of small- and large-conductance Ca(2+)-activated K(+) (SK and BK) channels increased TC amplitude and afferent nerve activity. After inhibiting detrusor muscle contractility, simulating the waveform of a TC by gently compressing the bladder evoked similar increases in afferent activity. Notably, afferent activity elicited by simulated TCs was augmented by SK channel inhibition. Our results show that afferent nerve activity evoked by TCs represents the majority of afferent outflow conveyed to the CNS during UB filling and suggest that the maximum TC rate of rise corresponds to an optimal length-tension relationship for efficient UB contraction. Furthermore, our findings implicate SK channels in controlling the gain of sensory outflow independent of UB contractility.

Influence on Strength and Flexibility of a Swing Phase-Specific Hamstring Eccentric Program in Sprinters' General Preparation.

Hamstring injuries are common in sprinters and mainly occur during the terminal swing phase. Eccentric training has been shown to reduce hamstring injury rate by improving several risk factors. The aim of this study was to test the hypothesis that an additional swing phase-specific hamstring eccentric training in well-trained sprinters performed at the commencement of the winter preparation is more efficient to improve strength, ratio, optimum angle, and flexibility than a similar program without hamstring eccentric exercises. Twenty sprinters were randomly allocated to an eccentric (n = 10) or a control group (n = 10). Both groups performed their usual track and field training throughout the study period. Sprinters in the eccentric group performed an additional 6-week hamstring eccentric program, which was specific to the swing phase of the running cycle (eccentric high-load open-chain kinetic movements covering the whole hamstring length-tension relationship preformed at slow to moderate velocity). Isokinetic and flexibility measurements were performed before and after the intervention. The eccentric group increased hamstring peak torques in concentric at 60° · s(-1) by 16% (p < 0.001) and at 240° · s(-1) by 10% (p < 0.01), in eccentric at 30° · s(-1) by 20% (p < 0.001) and at 120° · s(-1) by 22% (p < 0.001), conventional and functional ratios by 12% (p < 0.001), and flexibility by 4° (p < 0.01), whereas the control group increased hamstring peak torques only in eccentric at 30° · s(-1) by 6% (p ≤ 0.05) and at 120° · s(-1) by 6% (p < 0.01). It was concluded that an additional swing phase-specific hamstring eccentric training in sprinters seems to be crucial to address different risk factors for hamstring strain injuries, such as eccentric and concentric strength, hamstring-to-quadriceps ratio ratio, and flexibility.

Tenoscopic Suprapectoral Biceps Tenodesis

Existing arthroscopic techniques of proximal biceps tenodesis may be complicated by difficulty of tendon identification, restoration of length-tension relation, cosmetic deformity, persistent biceps pain, and shoulder stiffness requiring surgical revision in a relevant proportion of cases. In this context, biceps tenoscopy, an emerging discipline of shoulder endoscopy, offers major benefits. Tenoscopy comprises endoscopic treatment of tendons and tendon sheaths. The presented technique of tenoscopic suprapectoral biceps tenodesis (TSBT) substantially facilitates tendon identification and reduces invasiveness by avoidance of unnecessary surgical involvement of the deltoid space and bursa. TSBT enables effective treatment of the biceps tendon and surrounding tissues (biceps tendon sheath, tenosynovium, transverse humeral ligament) being consistently involved in proximal biceps pathologies. The physiological length-tension relation of the musculotendinous unit is reliably maintained. Technically, the procedure of tenodesis is simplified and accelerated by redundancy of tendon exteriorization. The aforementioned benefits of TSBT may lead to superior clinical and cosmetic outcomes and lower incidences of persistent proximal biceps pain and postoperative shoulder stiffness compared with conventional techniques of arthroscopic biceps tenodesis.

The Body & the Bike: A Kinetic Chain analysis of Cycling Overuse Injury

Introduction : Physiotherapists, osteopaths, doctors, bike-fitters and other cycling injury managers, are perfectly placed to help the ever-growing cycling community to become better riders as well as to prevent pain and injury. Whilst there are a myriad of “bike set-up” protocols available, some more evidence based than others, very few “bike set-up” practitioners take into account the body and its complex neuromuscular and kinematic abilities. There is no argument that understanding the geometry around optimal configuration is an important component for efficiency and injury prevention (Wisbey-Roth 2009), and some leading “Bike-Fit” proponents argue the neuromuscular perspective (Steve Hogg 2007). There are also endless references to optimal pedalling technique- “spinning the pedals”, “elegant”, “wipe the mud of the shoe”, “like a duck swimming” or “smooth and continuous”(Colson from Brukner and Khan 2012), implying that optimising activation patterns has a distinct role in good pedaling technique. Overuse injuries make up a large portion of injuries in aerobic sports that require long training sessions with a monotonous routine eg, long-distance running, bicycling or cross-country skiing (Bahr 2009). The greatest prevalence in overuse injuries in cycling is at the lumbar spine and knee, and efforts to prevent overuse injury should focus on these areas (Clarsen 2010). Maintaining or restoring precise movement of specific segments is the key to preventing or correcting musculoskeletal pain (Sahrmann 2002), and cycling injury management providers are clinically the best placed to be precise in the assessment and management of the movement patterns of the cyclist. Kinetic chain : The kinetic chain as a concept was first introduced in 1875, to describe the idea that the body was a collection of interacting segments, creating a system that would allow movement at one joint to affect movement of another joint within the kinetic link. Contemporary literature in the assessment and management of sporting injuries upholds the kinetic chain theory, with mechanical deficiency in one part of the activity chain being the cause of pathology in another part, especially in the case of ACL injury (Hewett 2005) and patello-femoral pain syndrome (Souza and Powers 2009). Cycling injury management has had a historical focus upon the position of the cyclist in relation to the bike, and justifiably so, but as the assessment of bike set-up evolves with the use of technology and sharing of information, deficiencies in the way the cyclist functions must become a part of the ideal bike set-up assessment. As a background we must explore the “Perfect” vs “Imperfect” technique of pedaling, and how this possible imperfect technique can be a source of pain or injury. And what are the measures which guide us in assessing that a pedal stroke is imperfect – kinematics, muscle activation, co-ordination, strength, length-tension relationships, force, power, posture? In the area of muscle activation, the historical perspective was simplistic, with the more realistic pattern represented in figure 1. And whilst the gluteals and quadriceps are seen as the main muscles for power production, co- ordination of the pedal stroke utilizing the hamstrings and calves seems an important feature of “perfect” pedaling (Figure 2 Blake 2012) FIGURE 2. Finally, given the paucity of research in the area of cause and effect regarding the kinetic chain and cycling injury, how much can we extrapolate findings for other athletes to the cyclist? Conclusion : pain and injury in the athletic population is complex in its aetiology. Clinical reasoning is essential to optimising management, and in cycling understanding the knowledge base regarding the interaction between the body and the bike is an important cornerstone to expert practice. The kinetic chain approach to analysis of cycling injury is a valid pathway and will bring cycling injury managers into line with world’s best practice in athletic injury management and prevention.

Undesirable effects of the eccentric isokinetic contractions

Even though sub-maximal eccentric exercises do not entail specific risks, the eccentric contractions at maximal intensity could increase the risk of injury in comparison with the other contraction modes. Based on the length-tension relationship, the maximal eccentric contraction allows to develop the highest torque (for instance on the isokinetic dynamometer), particularly in the elongated position of the muscle groups. Therefore, the injury risk is increased for the muscle, tendon and joint structures. In spite of specific safety mechanics inherent to the isokinetic tool, the risk of injury must be taken into consideration by the clinician. A quadriceps injury was reported in a professional soccer player subjected to eccentric testing of this muscle group at the occasion of a possible transfer. Do we consider such a testing as relevant? After surgical repair of the ACL, we refer to the possible risk for the graft in the case of maximal eccentric contraction of the quadriceps. Complaints frequently reported during eccentric contractions of the shoulder rotators are sometimes incompatible with testing, because of safety and measurement validity. Such an eccentric testing should concern mainly specialized healthy athletes involved in overhead gestures. The isokinetic dynamometer is also used for eccentric training and not only for testing. Strengthening in eccentric allows frequently improving very efficiently the maximal performance for this contraction mode, yet the improvement extent for the other modes remains controversial. On the other hand, intense and unusual eccentric exercises are known to induce Delayed Onset Muscle Soreness (DOMS). Although functional consequences of DOMS are transitory, they could disturb the rehabilitation and/or training process. Clinician and trainers must be aware of this side effect in order to amend their eccentric strengthening interventions.

The series elastic shock absorber: tendon elasticity modulates energy dissipation by muscle during burst deceleration.

During downhill running, manoeuvring, negotiation of obstacles and landings from a jump, mechanical energy is dissipated via active lengthening of limb muscles. Tendon compliance provides a 'shock-absorber' mechanism that rapidly absorbs mechanical energy and releases it more slowly as the recoil of the tendon does work to stretch muscle fascicles. By lowering the rate of muscular energy dissipation, tendon compliance likely reduces the risk of muscle injury that can result from rapid and forceful muscle lengthening. Here, we examine how muscle-tendon mechanics are modulated in response to changes in demand for energy dissipation. We measured lateral gastrocnemius (LG) muscle activity, force and fascicle length, as well as leg joint kinematics and ground-reaction force, as turkeys performed drop-landings from three heights (0.5-1.5 m centre-of-mass elevation). Negative work by the LG muscle-tendon unit during landing increased with drop height, mainly owing to greater muscle recruitment and force as drop height increased. Although muscle strain did not increase with landing height, ankle flexion increased owing to increased tendon strain at higher muscle forces. Measurements of the length-tension relationship of the muscle indicated that the muscle reached peak force at shorter and likely safer operating lengths as drop height increased. Our results indicate that tendon compliance is important to the modulation of energy dissipation by active muscle with changes in demand and may provide a mechanism for rapid adjustment of function during deceleration tasks of unpredictable intensity.

Effect of an eccentrically biased hamstring strengthening home program on knee flexor strength and the length-tension relationship.

The purposes of this study were to document relative activation intensities of the hamstrings and gluteus maximus during 4 eccentric hamstring strengthening exercises and to assess the effects of a short-term strengthening program comprised of these exercises on knee flexor strength and the length-tension relationship. Twelve healthy subjects participated in this study. Electromyographic (EMG) activities from the biceps femoris, semitendinosus, and gluteus maximus were recorded as subjects performed (a) standing hip extension with elastic resistance, (b) trunk flexion in single limb stance (diver), (c) standing split (glider), and (d) supine sliding bridge (slider). Baseline isometric knee flexor strength was measured at 90, 70, 50, and 30° of flexion at the knee with the subject seated and the hip flexed to 50° from horizontal. After completing the 4-week training program, strength tests were repeated. Repeated-measures analysis of variance were used to compare EMG activity between muscles and to assess angle-specific strength improvements. Hamstring activity exceeded gluteus maximus activity for resisted hip extension, glider, and slider exercises (p < 0.001) but not for the diver (p = 0.087). Hamstring activation was greatest during the slider and resisted hip extension and lowest during the glider and the diver. Knee flexor strength improved by 9.0% (p = 0.005) but was not angle specific (training by angle p = 0.874). The short-term home training program effectively targeted the hamstrings and resulted in strength gains that were similar at short and long muscle lengths. These data demonstrate that hamstring strength can be improved using eccentrically biased unilateral exercises without the use of weights or other equipments.

Workloop Contractions in Isolated Cardiac Myocytes Reflect in vivo Pressure-Volume Dysfunction in Rat Right Heart Failure

In pulmonary artery hypertension the right ventricle (RV) is more resistant to filling and is compromised in its ability to cope with increased demand. During the cardiac cycle, cardiomyocytes generate force isometrically, shorten during end-systole and are lengthened during diastolic filling, however intact cardiomyocyte function in vitro has classically been inferred from contractions with little or no external loading. We tested whether contractile function of isolated RV cardiomyocytes in high (isometric) and physiological (isometric and isotonic) loading conditions reflected in vivo dysfunction in rats with monocrotaline-induced (60 mg/kg) RV failure (FAIL). Workloop-style contractions were performed in electrically-paced (1Hz) intact isolated RV CON and FAIL cardiomyocytes at 37°C glued to glass fibres attached to a fast piezo length translator and high sensitivity optical force transducer (OptiForce, IonOptix).In vivo catheterisation revealed a tendency towards greater RV stroke work (CON 135±37μJ, FAIL 218±57μJ), steeper end-systolic pressure-volume relationship (PVR) (P<0.05) and a significantly steeper end-diastolic PVR (P<0.05) in FAIL compared to control rats (CON). In isolated cardiomyocytes, workloop area tended to be greater in FAIL cells (FAIL 5.4±0.8μJ, CON 3.4±0.8μJ, P=0.13). The end-systolic length-tension relationship (FAIL 0.15±0.03 μN/μm, CON 0.08±0.01 μN/μm, P<0.05) and end-diastolic length-tension relationship (FAIL 0.06±0.01 µN/µm (N=13), CON 0.03±0.01 µN/µm (N=8), P<0.05) measured by step length changes during isometric contractions were significantly steeper in FAIL. The isometric force-frequency relationship was positive in CON and negative in FAIL cells from 1-7Hz; the trend was the same but less pronounced in unloaded cells.We conclude that changes seen in vivo in RV FAIL hearts are at least partially caused by cellular contractile dysfunction.Grants from Boehringer Ingelheim Fonds and The Physiological Society to E.D.F. supported travel costs of this project.

Morphometry and anatomical variations of flexor digitorum superficialis

Abstract Introduction: Flexor digitorum superficialis (FDS) takes its origin by two heads: humero ulnar and radial.. The FDS is considered to be potential flexor of proximal interphalangeal, metacarpophalnageal and wrist joints through its insertion to the middle phalanges of lateral 4 fingers. Aim of the study was to conduct a morphometric study on FDS and to evaluate its variants in cadaveric limbs. Materials and Methods: The study was carried out on 25 right and 23 left upper limbs belonging to formalin fixed adult cadavers. Lengths of humeral, ulnar, radial heads of the muscle as well as its tendons were separately measured using digital caliper. Mean length of muscle bellies of humeral head, tendinous length and musculotendinous length tabulated. Results: A unique muscle belly arising from the deeper surface of left FDS as a tendon, proximal to flexor retinaculum, entering in the palm after passing through the carpal tunnel was observed. The muscle was inserted into the middle phalanx of index finger. Conclusion: Studies on absolute length of FDS are rare. The present study has significant influence on length tension relationship of afore mentioned muscle. The hazardous effects of anomalous belly of FDS and its consequences were also discussed.

Open subpectoral biceps tenodesis: reliable treatment for all biceps tendon pathology.

Long head of the biceps (LHB) tendon pathology is a common cause of pain in the shoulder. Pathology encountered includes biceps tendon tears and tendonitis, biceps anchor or superior labral tears, and biceps subluxation or instability. Current surgical treatment options for LHB disorders include tenotomy and tenodesis. Tenodesis prevents cosmetic deformity and biceps cramping with activity. Open subpectoral tenodesis anatomically restores the length-tension relationship of the biceps muscle and removes all diseased biceps from the bicipital groove. The authors present their technique of open subpectoral tenodesis, which demonstrates a high success rate with consistent pain relief and dependable fixation.

Arthroscopic Suprapectoral and Open Subpectoral Biceps Tenodesis: A Comparison of Restoration of Length-Tension and Mechanical Strength Between Techniques

This study aimed to (1) evaluate the exvivo restoration of the long head biceps length-tension for both arthroscopic suprapectoral biceps tenodesis (ASPBT) and open subpectoral biceps tenodesis (OSPBT) techniques and (2) assess how location in the proximal humerus affects pullout strength for tenodesis using an interference screw implant. Eighteen matched cadaveric shoulders were randomized to OSPBT or ASPBT groups (9 each). Tenodesis was performed using clinical techniques. Preoperatively, a metallic bead was placed in the biceps tendon and a fluoroscopic image was obtained. Postoperatively, an image was obtained to evaluate the location of the tenodesis and the metallic bead and determine tensioning. Biomechanical load-to-failure testing was then performed. The ASPBT technique resulted in an average of 2.15 ± 0.62 cm of biceps overtensioning compared with 0.78 ± 0.35 cm (P < .001) in the OSPBT group. The average load to failure in the ASPBT group was 138.8 ± 29.1 N compared with 197 ± 38.6 N (P= .002) in the OSPBT group. Failure caused by implant pullout was significantly more frequent in the ASPBT group (7 of 9) than in the OSPBT group (1 of 9). The described ASPBT technique using an interference screw implant has the tendency to overtension the biceps and has a significantly decreased ultimate load to failure compared with an open subpectoral technique in matched cadaveric specimens. This study shows differences in the biomechanical properties of OSPBT and ASPBT. Modification of currently published ASPBT techniques may be necessary to improve restoration of the physiological length-tension relationship of the biceps. Clinical studies may need to clarify if the lower ultimate load to failure for the ASPBT technique is clinically significant.

Equilibrium-based movement endpoints elicited from primary motor cortex using repetitive microstimulation.

High-frequency, long-duration intracortical microstimulation (HFLD-ICMS) is increasingly being used to deduce how the brain encodes coordinated muscle activity and movement. However, the full movement repertoire that can be elicited from the forelimb representation of primary motor cortex (M1) using this method has not been systematically determined. Our goal was to acquire a comprehensive M1 forelimb representational map of movement endpoints elicited with HFLD-ICMS, using stimulus parameters optimal for evoking stable forelimb spatial endpoints. The data reveal a 3D forelimb movement endpoint workspace that is represented in a patchwork fashion on the 2D M1 cortical surface. Although cortical maps of movement endpoints appear quite disorderly with respect to movement space, we show that the endpoint locations in the workspace evoked with HFLD-ICMS of two adjacent cortical points are closer together than would be expected if the organization were random. Although there were few obvious consistencies in the endpoint maps across the two monkeys tested, one notable exception was endpoints bringing the hand to the mouth, which was located at the boundary between the hand and face representation. Endpoints at the extremes of the monkey's workspace and locations above the head were largely absent. Our movement endpoints are best explained as resulting from coactivation of agonist and antagonist muscles driving the joints toward equilibrium positions determined by the length-tension relationships of the muscles.

Effect of Knee Joint Angle on Side-to-Side Strength Ratios

Isometric knee extensor and flexor strength are typically tested at different joint angles due to the differences in length-tension relationships of the quadriceps and hamstring muscles. The efficiency of strength testing can be improved if the same angle can be used to test both the knee extensor and flexor muscle groups. The aim of this study was to determine an optimal angle for isometric knee strength testing by examining the effect of knee angle on side-to-side peak torque ratios. Eighteen active young people (9 males and 9 females) participated in this study. Knee extensor and knee flexor strength were tested on both sides at 30°, 60°, and 90° of knee flexion. The effect of knee flexion angle on side-to-side peak torque ratios, raw torque values, and side-to-side flexor-to-extensor torque ratios were assessed. Side-to-side knee extensor peak torque ratios and knee flexor-to-extensor torque ratios differed significantly by knee flexion angle (p = 0.024 and p = 0.011, respectively), but side-to-side knee flexor peak torque ratios did not differ significantly (p = 0.311). When considering both side-to-side peak torque ratios and flexor-to-extensor torque ratios, the values were more symmetrical (i.e., closer to 100%) only at 60° of knee flexion. Our results indicate that both the knee flexors and the knee extensors can be tested clinically at 60° of knee flexion. Our results also indicate that the hamstrings can be tested at any of the 3 angles if the examiner is interested in side-to-side ratios rather than raw torque values. These results may facilitate more efficient and flexible clinical knee strength testing.

Alterations in thin filament length during postnatal skeletal muscle development and aging in mice.

The lengths of the sarcomeric thin filaments vary in a skeletal muscle-specific manner and help specify the physiological properties of skeletal muscle. Since the extent of overlap between the thin and thick filaments determines the amount of contractile force that a sarcomere can actively produce, thin filament lengths are accurate predictors of muscle-specific sarcomere length-tension relationships and sarcomere operating length ranges. However, the striking uniformity of thin filament lengths within sarcomeres, specified during myofibril assembly, has led to the widely held assumption that thin filament lengths remain constant throughout an organism's lifespan. Here, we rigorously tested this assumption by using computational super-resolution image analysis of confocal fluorescence images to explore the effects of postnatal development and aging on thin filament length in mice. We found that thin filaments shorten in postnatal tibialis anterior (TA) and gastrocnemius muscles between postnatal days 7 and 21, consistent with the developmental program of myosin heavy chain (MHC) gene expression in this interval. By contrast, thin filament lengths in TA and extensor digitorum longus (EDL) muscles remained constant between 2 mo and 2 yr of age, while thin filament lengths in soleus muscle became shorter, suggestive of a slow-muscle-specific mechanism of thin filament destabilization associated with aging. Collectively, these data are the first to show that thin filament lengths change as part of normal skeletal muscle development and aging, motivating future investigations into the cellular and molecular mechanisms underlying thin filament adaptation across the lifespan.

Arthroscopic Suprapectoral and Open Subpectoral Biceps Tenodesis: A Comparison of Location, Restoration of Length-Tension and Mechanical Strength Between Techniques

Objectives:The approach to biceps tenodesis remains controversial, as the procedure can be performed open or arthroscopically. Little data exists directly comparing the arthroscopic suprapectoral and open subpectoral techniques, particularly in terms of location, restoration of the long head biceps length-tension relationship, and the mechanical strength of the tenodesis. The purpose of this study was to (1) determine the in-vivo tenodesis location using arthroscopic suprapectoral (ASPBT) and open subpectoral techniques (OSPBT) for long head biceps tenodesis and compare this to the location achieved in a separate clinical cohort, (2) evaluate the in-vivo restoration of the long head biceps length-tension relationship for both ASPBT and OSPBT techniques and (3) assess how location in the proximal humerus (suprapectoral or subpectoral) and method of fixation affects pull-out strength for biceps tenodesis using an interference screw implant. Our null hypothesis was that no difference existed between ASPBT and OSPBT with regards to location, restoration of the length-tension relationship, and pull-out strength.Methods:18 matched cadaveric shoulder specimens were randomized to either open subpectoral or arthroscopic suprapectoral tenodesis groups (9 open, 9 arthroscopic.) Tenodesis was performed by two sports fellowship-trained surgeons using identical clinical techniques. Prior to surgery, a metallic bead was sutured in place, 1 cm distal to the musculotendinous junction of the long head of the biceps, and a pre-operative fluoroscopic image was obtained. Post-operatively, an additional fluoroscopic image was obtained to evaluate the location of the tenodesis and the metallic bead, which was compared to the pre-operative image to determine tensioning (Fig 1). Biomechanical testing was then performed using a MTS machine with 2.5kN load cell. Constructs were cycled for 100 cycles, then load to failure testing was performed.Results:The average tenodesis location in the ASPBT group of cadaveric specimens was 4.68 cm ± 0.97 cm distal to the top of the humerus, compared with 7.46 cm ± 1.7 cm (p < 0.0001) in the OSPBT group. This was very similar to the location observed in a separate clinical cohort. The ASPBT technique resulted in an average of 2.15 ± 0.62 cm of biceps over-tensioning compared with 0.78 ± 0.35 cm (p < 0.001) in the OSPBT group. The average load to failure in the ASPBT group was 138.8 ± 29.1 N compared to 197 ± 38.6 N (p = 0.002) in the OSPBT group. Implant pullout was significantly more frequent in the ASPBT (7/9) compared to the OSPBT (1/9) group.Conclusion:This study revealed several notable differences between the arthroscopic suprapectoral and open subpectoral biceps tenodesis techniques. The described ASPBT technique using an interference screw implant results in a more proximal tenodesis location, has the tendency to over-tension the biceps and has a significantly decreased ultimate load to failure compared with an open subpectoral technique in matched cadaver specimens. Modification of currently published arthroscopic suprapectoral techniques is necessary to improve restoration of the physiologic length-tension relationship of the biceps. Improved implants are likely necessary to achieve equivalent construct strength to the open subpectoral technique, although the clinical ramifications of this strength discrepancy have not been established.

Effects Of Contract-relax Versus Static Stretching On Strength Loss And The Length-tension Relationship

Effects Of Contract-relax Versus Static Stretching On Strength Loss And The Length-tension Relationship