Isometric Quadriceps Force Research Articles

Climbing Out of Our Silos to Improve Practice

When I sit back to “take in” the content of our May issue, several thoughts come to mind that I want share with you. First and foremost, each article is relevant to our readers, regardless of the breadth of the content represented. I know how very busy we all are, but I truly believe that our specialty content is enriched when we climb out of our silos of “expertise and comfort” and read about research findings in other areas. The article by Farquhar et al,1 “Persistence of Altered Movement Patterns During a Sit-to-Stand Task 1 Year Following Unilateral Total Knee Arthroplasty,” will immediately attract those who are interested in musculoskeletal diagnoses. I would contend, however, that the message offered by this article is more universal and is an important addition to the findings of a 2004 paper that described outcomes of an evidence-based, high-quality intervention after total joint arthroplasty.2 At 1 year postsurgery, the intensive intervention (17 visits over 6 weeks) helped participants return to age-, height-, and body mass index–matched control levels for quadriceps isometric force production and functional performance. Success? Well, it depends. When the investigators examined the movement patterns used to stand from a chair, the people with total knee arthroplasty demonstrated an increased hip flexion and a larger hip extensor moment reminiscent of a compensatory strategy to “protect” a painful knee. This finding raises all sorts of questions, regardless of content expertise. Is it possible to teach movement strategies that become automatic? What is the most effective approach to enhance motor learning, and would degenerative consequences to the other joints be reduced if the compensatory strategy was replaced? Bear with me as I ask you to consider another article that many of you might believe is far outside of your area: “Locomotor Training Restores …

An acute bout of static stretching: effects on force and jumping performance.

The objectives of this study were to examine whether a static stretching (SS) routine decreased isometric force, muscle activation, and jump power while improving range of motion (ROM). Second, the study attempted to compare the duration of the dependent variable changes with the duration of the change in ROM. Twelve participants were tested pre- and post- (POST, 30, 60, 90, and 120 min) SS of the quadriceps and plantar flexors (PF) or a similar period of no stretch (control). Measurements during isometric contractions included maximal voluntary force (MVC), evoked contractile properties (peak twitch and tetanus), surface integrated electromyographic (iEMG) activity of the agonist and antagonistic muscle groups, and muscle inactivation as measured by the interpolated twitch technique (ITT). Vertical jump (VJ) measurements included unilateral concentric-only (no countermovement) jump height as well as drop jump height and contact time. ROM associated with seated hip flexion, prone hip extension, and plantar flexion-dorsiflexion was also recorded. After SS, there were significant overall 9.5% and 5.4% decrements in the torque or force of the quadriceps for MVC and ITT, respectively. Force remained significantly decreased for 120 min (10.4%), paralleling significant percentage increases (6%) in sit and reach ROM (120 min). After SS, there were no significant changes in jump performance or PF measures. The parallel duration of changes in ROM and quadriceps isometric force might suggest an association between stretch-induced changes in muscle compliance and isometric force output.

The Effects of Estrogen on Indices of Skeletal Muscle Tissue Damage after Eccentric Exercise in Postmenopausal Women

This study examined if estrogen (E) usage (in the form of hormone replacement therapy [HRT]) has a protective effect on skeletal muscle damage in postmenopausal women. Nine postmenopausal women (age 55.2 +/- 9.9 [mean +/- SD]) performed two exercise sessions at 70% of their maximal heart rate on HRT (E-HI) and without HRT (E-LO; following a 28-45 day HRT washout). All subjects followed a condition order of E-HI then E-LO with at least 42 days between exercise sessions. Serum creatine kinase (CK), perceived delayed onset muscle soreness (DOMS), and maximal quadriceps isometric force (MIF) were taken pre-exercise, 24, 48 and 72-hr post exercise. E-HI and E-LO conditions produced a rise in CK (p < 0.001) after exercise; but CK after E-HI was greater than in E-LO (p < 0.001) at 24 hours and at 48 hours. DOMS was significantly elevated at 24, 48, and 72-hr post each exercise session (p < 0.05). The greatest peak DOMS score occurred during the E-HI condition. MIF was similarly reduced after each exercise session (p < 0.05). These results suggest elevated E does not offer a protective effect to skeletal muscle; however, design limitations (i.e., condition order) confound the present data. Interestingly, an association between peak-CK during the E-LO condition and the number of washout days (r = +0.707, p < 0.05) between conditions existed. This suggests a longer washout period may be necessary to elucidate the actual E effects on skeletal muscle. These findings suggest that more work correcting for the present design limitations is warranted on this topic.

Removal of the lateral or medial third of patellar tendon alters the patellofemoral contact pressure and area: an in vitro experimental study in dogs

Objectives. To compare patellofemoral contact pressure and areas after immediate removal of the lateral, central, or medial third of patellar tendon. Design. In vitro experiment in 12 dogs. Background. Alteration of the vector sum of the quadriceps muscle contraction after removal of partial patellar tendon might result in changes of patellar tracking in the trochlea. Methods. Patellofemoral contact pressure and areas were recorded using Fuji pressure-sensitive film at 45°, 60°, and 90° of knee flexion under an isometric quadriceps force of 100% body weight. The patellofemoral contact imprint from the intact knees were obtained as control, and the lateral ( n=4), central ( n=4), and medial ( n=4) third of the patellar tendon were subsequently removed and the patellofemoral contact imprint was recorded. Results. The patellofemoral contact area was found to increase with increasing knee flexion angles. No change in patellofemoral contact pressure and areas was found after removal of the central third patellar tendon. However, after removal of either lateral or medial third of patellar tendon, the patellofemoral contact was rotated with increasing knee flexion angles. This was due to the altered vector sum of the quadriceps force, resulting in significantly decreased patellofemoral contact areas and simultaneously a significantly increased contact pressure, characterized with concentration of patellofemoral contact pressure on both lateral and medial facets of the patellofemoral joint. Conclusions. The results suggest that removal of the central third of patellar tendon may not alter the patellofemoral contact pressure and areas as compared with removal of either lateral or medial third of patellar tendon that may result in an altered postoperative tracking mechanism of the patellofemoral joint immediately after operation. Relevance Findings of this in vitro animal study supports the use of central third of patellar tendon as autograft for anterior cruciate ligament reconstruction. However, further experimental studies are needed to investigate how the postoperative healing of the host patellar tendon will influence the findings obtained from this in vitro study.

Leg extensor power and quadriceps strength: an assessment of repeatability in patients with osteoarthritic knees.

To assess the repeatability of two muscle function measures -- leg extensor power (LEP) and isometric quadriceps force (IQF) -- in a population of patients with osteoarthritis of the knee. Repeat measures of LEP and IQF at 25 degrees and 50 degrees knee flexion were taken within seven days. Both legs were measured and a numerical rating scale was used to assess pain on the two occasions. Patients who were on a waiting list for a primary unilateral knee replacement for osteoarthritis were invited to take part in the study. The physiotherapy department of a National Health Service Orthopaedic Hospital in Oxford, UK. Subjects were measured using a Kin-Com dynamometer to assess maximum isometric force and a leg extensor power rig to assess maximum single leg explosive power. Twenty-six patients (mean age: 72 years; SD: 8 years; range: 50-87 years) were included in the study following informed consent. A weak relationship was found between LEP, IQF and pain scores which reached the 5% significance level for the LEP measures only. The level of repeatability for both measures was found to be acceptable. Both LEP and IQF are recommended as repeatable measures for assessment of muscle function in patients with osteoarthitis of the knee. However, the LEP rig has the added advantage of being quicker, cheaper and simpler to use in the clinical setting.

Peripheral muscle weakness contributes to exercise limitation in COPD.

Recently, it was suggested that fatigue of peripheral muscles could contribute to exercise limitation in patients with chronic obstructive pulmonary disease (COPD). In order to quantify the role of peripheral muscle force, we restudied potential determinants of exercise capacity (6-min walking distance [6 MWD] and maximal oxygen consumption [V02max]) in 41 consecutive COPD patients (FEV1, 43 +/- 19% of predicted, TLCO, 56 +/- 25% of predicted) admitted to our pulmonary rehabilitation program. VO2max (incremental cycle ergometer test), 6 MWD (best of three), lung function (FEV1, FVC, TLC, FRC), diffusing capacity (TLCO), isometric quadriceps force (QF), hand grip force (HF), and maximal inspiratory (PImax) and expiratory (PEmax) pressures were measured. Patients had a poor 6 MWD (372 +/- 136 m) and VO2max (1.35 +/- 0.60 L, 71%), reduced respiratory (PImax 65 +/- 27%) and peripheral muscle force (QF 74 +/- 27%, HF 82 +/- 23%). In single regression analysis, significant correlations (r) were found for VO2max and TLCO (0.68), FEV1 (0.64), QF (0.55), HF (0.53), and body weight (0.49). Walking distance was significantly correlated with QF (0.63), HF (0.61), PImax (0.49), and TLCO (0.38). In stepwise multiple regression analysis, the variables significantly contributing to 6 MWD were QF and Plmax. For VO2max, variables significantly contributing were TLCO, QF, and FEV1. We conclude that lung function and peripheral muscle force are important determinants of exercise capacity in COPD.