Maximal Isometric Knee Extension Torque Research Articles

The mobility limitation in healthy older people is due to weakness and not slower muscle contractile properties.

The maximal power generating capacity of a muscle declines with age and has a negative impact on the performance of daily life activities. As muscle power is the product of force and velocity, we recruited 20 young (10 men, 10 women: 20–31 years) and 20 older (10 men, 10 women: 65–86 years) people to investigate which of these components contributes to the lower power and performance in old age. After determination of the maximal isometric knee extension torque (MVC), they performed a countermovement jump (CMJ) in 1) the normal situation (normal), 2) with an extra load of 15% body weight (loaded) and 3) 15% lower body weight (unloaded with a pulley system), and a timed up-and-go test (TUG) in the normal or loaded condition. The TUG and CMJ performance was lower in old than young participants (p<0.001). Below a critical CMJ peak power of ~23.7 W·kg-1 TUG showed a progressive decrease. The CMJ take-off velocity (Voff) in the normal condition was lower in old than young participants (p<0.001). However, the Voff vs. body weight/MVC relationship of the normal, loaded and unloaded data combined was similar in the old and young participants and fitted the Hill equation (R2 = 0.396). This indicates that 1) only when peak power drops below a critical threshold TUG becomes impaired and 2) there was no evidence for intrinsic slowing of the muscle contractile properties in older people, but rather the older people were working on a slower part of the force-velocity relationship due to weaker muscles.

Long-term assessment of morphological, functional, and quantitative parameters of skeletal muscle in older patients after unilateral total hip arthroplasty.

Total hip arthroplasty (THA) is performed for pain relief in patients with osteoarthritis of the hip joint. After THA, patients may recover muscle mass and physical function. Muscle quality is the main parameter used to indicate intramuscular fat content, and it is related with muscle function in older individuals. However, how THA affects muscle quality, as determined by echo intensity (EI), is not well understood. The purpose of this study was to determine the long-term characteristics of EI, muscle quantity, muscle function, and physical functions in the patients with THA surgery. In order to achieve the purpose, we performed two comparison. First, we compared muscle EI, quantity and function in operated leg with unoperated legs in the same patients and with the legs of healthy adults (i.e., both unoperated legs). Second, we compared physical functional tests between THA patient and age and body composition matched controls. Twenty-two older individuals (age: 67.1±5.3years, height: 160.9±7.1cm, body mass: 62.6±16.1kg) who underwent unilateral THA several (5.2±3.1) years ago (THA group) and 22 healthy controls with matching age and body composition (age: 68.3±4.4years, height: 160.3±7.9cm, body mass: 61.7±7.8kg) (CON group) participated in this case-control study. EI, an index of muscle quality, and muscle thickness (MT), an index of muscle quantity, were measured from B-mode transverse images of the rectus femoris obtained through ultrasound. The maximal isometric knee extension torque was measured in both the operated and unoperated legs in the THA group and in the right leg in the CON group (control leg); physical function tests, such as sit-to-stand, walking speed, hip adduction, and abduction torque assessments, were performed in both groups. MT and maximal isometric knee extension torque in operated leg were not different with unoperated, and control legs; the EI in the operated leg was significantly higher than that in the control leg (106.9±16.9 vs. 92.4±21.0a.u., P<0.05). The THA group demonstrated slower walking speed and lower hip abduction torque than the CON group (walking speed: 1.3±0.2 vs. 1.5±0.2m/s; hip abduction torque 1.2±0.3 vs. 1.5±0.5Nm/kg, P<0.05). Several years after THA, the operated legs completely recovered the same level of muscle quantity as that in healthy participants but with lower muscle quality and hip joint function. These defects may be associated with locomotive dysfunction in older THA patients.

Localization of muscle damage within the quadriceps femoris induced by different types of eccentric exercises

This study examined localization of muscle damage within the quadriceps femoris induced by different types of eccentric exercises by using transverse relaxation time (T2 )-weighted magnetic resonance imaging (MRI). Thirty-three young males performed either of the following three exercises: single-joint eccentric contraction of the knee extensors (KE), eccentric squat (S), or downhill walking (DW) (n=11/exercise). KE and S consisted of 5-set×10-lowering of 90% one-repetition maximum load. DW was performed for 60minutes with -10% slope, 6km/h velocity, and 20% body mass load carried. At pre- and 24-, 48-, and 72-hours post-exercise, T2 -MRI was scanned and T2 values for the rectus femoris (RF), vastus intermedius (VI), vastus lateralis (VL), and vastus medialis (VM) at proximal, middle, and distal sites were calculated. Additionally, soreness felt when static pressure was applied to these sites and maximal isometric knee extension torque were measured. Maximal torque significantly (P<.05) decreased (7%-15%) at 24-48hours after all exercises. T2 significantly increased (3%-9%) at 24-72hours after all exercises, with heterogeneities within the muscles found in each exercise. Effect size and peak change of T2 , as well as soreness, overall indicated that the proximal RF after KE and middle VM after S and DW were most affected by these exercises. The VL did not show any significant T2 increase after all exercises. These results suggest that muscle damage specifically localizes at the proximal RF by KE and at the middle VM by S and DW, while the VL is least damaged regardless of the exercises.

Knee-Extension Torque Variability and Subjective Knee Function in Patients with a History of Anterior Cruciate Ligament Reconstruction.

When returning to physical activity, patients with a history of anterior cruciate ligament reconstruction (ACL-R) often experience limitations in knee-joint function that may be due to chronic impairments in quadriceps motor control. Assessment of knee-extension torque variability may demonstrate underlying impairments in quadriceps motor control in patients with a history of ACL-R. To identify differences in maximal isometric knee-extension torque variability between knees that have undergone ACL-R and healthy knees and to determine the relationship between knee-extension torque variability and self-reported knee function in patients with a history of ACL-R. Descriptive laboratory study. Laboratory. A total of 53 individuals with primary, unilateral ACL-R (age = 23.4 ± 4.9 years, height = 1.7 ± 0.1 m, mass = 74.6 ± 14.8 kg) and 50 individuals with no history of substantial lower extremity injury or surgery who served as controls (age = 23.3 ± 4.4 years, height = 1.7 ± 0.1 m, mass = 67.4 ± 13.2 kg). Torque variability, strength, and central activation ratio (CAR) were calculated from 3-second maximal knee-extension contraction trials (90° of flexion) with a superimposed electrical stimulus. All participants completed the International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form, and we determined the number of months after surgery. Group differences were assessed using independent-samples t tests. Correlation coefficients were calculated among torque variability, strength, CAR, months after surgery, and IKDC scores. Torque variability, strength, CAR, and months after surgery were regressed on IKDC scores using stepwise, multiple linear regression. Torque variability was greater and strength, CAR, and IKDC scores were lower in the ACL-R group than in the control group (P < .05). Torque variability and strength were correlated with IKDC scores (P < .05). Torque variability, strength, and CAR were correlated with each other (P < .05). Torque variability alone accounted for 14.3% of the variance in IKDC scores. The combination of torque variability and number of months after surgery accounted for 21% of the variance in IKDC scores. Strength and CAR were excluded from the regression model. Knee-extension torque variability was moderately associated with IKDC scores in patients with a history of ACL-R. Torque variability combined with months after surgery predicted 21% of the variance in IKDC scores in these patients.

Knee extension torque variability after exercise in ACL reconstructed knees.

The purpose of this study was to compare knee extension torque variability in patients with ACL reconstructed knees before and after exercise. Thirty two patients with an ACL reconstructed knee (ACL-R group) and 32 healthy controls (control group) completed measures of maximal isometric knee extension torque (90° flexion) at baseline and following a 30-min exercise protocol (post-exercise). Exercise included 30-min of repeated cycles of inclined treadmill walking and hopping tasks. Dependent variables were the coefficient of variation (CV) and raw-change in CV (ΔCV): CV = (torque standard deviation/torque mean x 100), ΔCV = (post-exercise - baseline). There was a group-by-time interaction (p = 0.03) on CV. The ACL-R group demonstrated greater CV than the control group at baseline (ACL-R = 1.07 ± 0.55, control = 0.79 ± 0.42, p = 0.03) and post-exercise (ACL-R = 1.60 ± 0.91, control = 0.94 ± 0.41, p = 0.001). ΔCV was greater (p = 0.03) in the ACL-R group (0.52 ± 0.82) than control group (0.15 ± 0.46). CV significantly increased from baseline to post-exercise (p = 0.001) in the ACL-R group, while the control group did not (p = 0.06). The ACL-R group demonstrated greater knee extension torque variability than the control group. Exercise increased torque variability more in the ACL-R group than control group.

Repeated Bouts of Exercise in Patients with Anterior Cruciate Ligament Reconstruction

Reduced quadriceps activation after anterior cruciate ligament reconstructions (ACL-R) has been reported. Patients often return to daily exercise or sport after ACL-R; however, there is little information regarding quadriceps function after exercise in this population. Therefore, the purpose of this study was to compare quadriceps strength and central activation after repeated bouts of exercise between individuals with and without a history of ACL-R. Eighteen recreationally active subjects participated in this study: 8 with unilateral ACL-R at least 6 months earlier and 10 healthy controls. All subjects performed 30 min of continuous exercise on two consecutive days. Exercise included repeated bouts of inclined treadmill walking and jumping exercises. We measured maximal isometric knee extension torque and quadriceps central activation ratio (CAR) using the superimposed burst technique before and after exercise on day 1. Subjects returned 24 h later (day 2) for a repeat testing session. There was a significant group-time interaction for knee extension torque. ACL-R subjects were weaker at baseline on day 1 of testing (P = 0.01) but exhibited no significant reduction in knee extension torque after exercise (P = 0.13), whereas the healthy control subjects did (P = 0.01). Knee extension torque on day 2 remained significantly lower than baseline for the controls (P = 0.03), but not the ACL-R (P = 0.73). On day 2, both groups experienced significantly reduced knee extension torque after exercise. There was no group-time interaction for CAR, but a group main effect indicated that, on average, ACL-R had significantly lower CAR bilaterally compared with healthy controls. The quadriceps in ACL-R knees were weaker and showed less reduction of isometric knee extension torque compared with healthy group in day 1. However, there were no group differences of quadriceps strength on day 2.

Induced Anterior Knee Pain Immediately Reduces Involuntary and Voluntary Quadriceps Activation

To examine the immediate effects of experimentally induced anterior knee pain (AKP) on involuntary and voluntary quadriceps strength and activation. Crossover 3 × 3 randomized controlled laboratory study with repeated measures. Human Performance Research Center, Brigham Young University. Thirteen neurologically sound volunteers (age, 21.9 ± 3.2 years). Subjects underwent 3 different conditions (pain, sham, and control). To induce AKP and sham condition, 5% sodium chloride and 0.9% sodium chloride (total volume of 1.0 mL for each condition), respectively, were injected into the infrapatellar fat pad on the dominant leg. No injection was performed for the control condition. The vastus medialis peak Hoffmann reflex normalized by the peak motor response (H:M ratio) was used to measure involuntary quadriceps activation. Quadriceps central activation ratio (CAR) using maximal isometric knee extension torque (N·m) was calculated to assess voluntary quadriceps activation. The visual analog scale was used to measure pain perception. Our pain model increased perceived pain immediately after the 5% hypertonic saline injection and pain lasted for 12 minutes on average (F40,743 = 16.85, P < 0.001). During the pain condition, subjects showed a 12% decrease in H:M ratio (F2,59 = 8.64, P < 0.001), a 34% decrease in maximal isometric knee extension torque (F2,59 = 5.89, P < 0.01), and a 5% decrease in CAR (F2,59 = 3.83, P = 0.03). Our data showed that joint pain may be an independent factor to alter function of the muscles surrounding the painful joint. Both involuntary and voluntary inhibitory pathways may play a role in an immediate reduction of muscle activation.

Long-term Aerobic Exercise Is Associated With Greater Muscle Strength Throughout the Life Span

Aging is associated with a progressive decline in muscle strength, muscle mass, and aerobic capacity, which reduces mobility and impairs quality of life in elderly adults. Exercise is commonly employed to improve muscle function in individuals of all ages; however, chronic aerobic exercise is believed to largely impact cardiovascular function and oxidative metabolism, with minimal effects on muscle mass and strength. To study the effects of long-term aerobic exercise on muscle strength, we recruited 74 sedentary (SED) or highly aerobically active (ACT) men and women from within three distinct age groups (young: 20-39 years, middle: 40-64 years, and older: 65-86 years) and tested their aerobic capacity, isometric grip and knee extensor strength, and dynamic 1 repetition maximum knee extension. As expected, ACT subjects had greater maximal oxygen uptake and peak aerobic power output compared with SED subjects (p < .05). Grip strength relative to body weight declined with age (p < .05) and was greater in ACT compared with SED subjects in both hands (p < .05). Similarly, relative maximal isometric knee extension torque declined with age (p < .05) and was higher in ACT versus SED individuals in both legs (p < .05). Absolute and relative 1 repetition maximum knee extension declined with age (p < .05) and were greater in ACT versus SED groups (p < .05). Knee extensor strength was associated with a greater amount of leg lean mass in the ACT subjects (p < .05). In summary, long-term aerobic exercise appears to attenuate age-related reductions in muscle strength in addition to its cardiorespiratory and metabolic benefits.

Effects of Low-Load Resistance Training with Vascular Occlusion on the Mechanical Properties of Muscle and Tendon

The present study aimed to investigate the effects of low-load resistance training with vascular occlusion on the specific tension and tendon properties by comparing with those of high-load training. Nine participants completed 12 weeks (3 days/week) of a unilateral isotonic training program on knee extensors. One leg was trained using low load (20% of 1 RM) with vascular occlusion (LLO) and other leg using high load (80% of 1 RM) without vascular occlusion (HL). Before and after training, maximal isometric knee extension torque (MVC) and muscle volume were measured. Specific tension of vastus lateralis muscle (VL) was calculated from MVC, muscle volume, and muscle architecture measurements. Stiffness of tendon-aponeurosis complex in VL was measured using ultrasonography during isometric knee extension. Both protocols significantly increased MVC and muscle volume of quadriceps femoris muscle. Specific tension of VL increased significantly 5.5% for HL, but not for LLO. The LLO protocol did not alter the stiffness of tendon-aponeurosis complex in knee extensors, while the HL protocol increased it significantly. The present study demonstrated that the specific tension and tendon properties were found to remain following low-load resistance training with vascular occlusion, whereas they increased significantly after high-load training.

Muscular adaptation to concentric and eccentric exercise at equal power levels

The effect of training with concentric and eccentric contractions on fiber hypertrophy and isometric torque production was investigated in 20 healthy subjects. One group (eight female and two male subjects) performed concentric contractions of their quadriceps femoris muscles at an intensity of 90% of their maximal concentric power. The other group (six female and four male subjects) performed eccentric contractions at the same relative power level. Both groups exercised three times per week for 4 wk at a constant speed of 60 degrees.s-1 on a Kin-Com dynamometer. Needle biopsies were obtained from the vastus lateralis before and after the exercise program. Fiber-type differentiation was performed using a myosin ATPase stain at a preincubation of 10.5. Maximal isometric knee extension torque was also measured before and after the exercise program. An analysis of covariance was used to determine whether there were significant differences between the exercise groups in: 1) the post-exercise fiber areas and 2) maximal isometric torque (MIso), while controlling for initial differences. Results showed a significant difference between the Type II fiber areas (P < 0.01) and the MIso (P = 0.01). These data indicate that, when exercising at the same relative power level, a subject performing concentric contractions will show greater muscle hypertrophy and improve in MIso production more than a subject training with eccentric contractions.

Compatibility of adaptive responses with combining strength and endurance training

Impairment in strength development has been demonstrated with combined strength and endurance training as compared with strength training alone. The purpose of this study was to examine the effects of combining conventional 3 d.wk-1 strength and endurance training on the compatibility of improving both VO2peak and strength performance simultaneously. Sedentary adult males, randomly assigned to one of three groups (N = 10 each), completed 10 wk of training. A strength-only (S) group performed eight weight-training exercises (4 sets/exercise, 5-7 repetitions/set), an endurance-only (E) group performed continuous cycle exercise (50 min at 70% heart rate reserve), and a combined (C) group performed the same S and E exercise in a single session. S and C groups demonstrated similar increases (P < 0.0167) in 1RM squat (23% and 22%) and bench press (18% for both groups), in maximal isometric knee extension torque (12% and 7%), in maximal vertical jump (6% and 9%), and in fat-free mass (3% and 5%). E training did not induce changes in any of these variables. VO2peak (ml.kg-1.min-1) increased (P < 0.01) similarly in both E (18%) and C (16%) groups. Results indicate 3 d.wk-1 combined training can induce substantial concurrent and compatible increases in VO2peak and strength performance.

Fatigue effects of marathon running on neuromuscular performance

Nine experienced endurance runners performed individual marathon runs that involved several tests of neuromuscular performance before, during and after the marathon. The tests were performed with special force platform and dynamometer techniques. The results showed an overall decrease in performance from the marathon. The maximal sprint velocity decreased parabolically during the marathon, reaching the final value of 84% of the pre‐marathon one. Similarly, the other test results after marathon indicated that maximal isometric knee extension torque was 78%, the performance in a special rebound test (drop jump) 84% and the 5‐jump performance 92% of the pre‐marathon values. These reductions were accompanied by alteration in the ground reaction force curves in the sprint and jump tests, suggesting reduced tolerance to stretch load as well as loss in the recoil characteristics of the muscles.