Eccentric Quadriceps Research Articles

EFFECTS OF HEAVY RESISTANCE TRAINING ON MUSCLE PROFILE, STRENGTH AND SOCCER PERFORMANCE IN FEMALE ELITE SOCCER PLAYERS.

PURPOSE: The aim of the present study was to evaluate the effect of heavy resistance training on maximal and ‘explosive' muscle strength, soccer performance and muscle morphology of female elite soccer players. METHODS: 16 players were tested at end of autumn season (P1), after 12 weeks of either isolated heavy resistance training (1.7 sessions/wk) (HRT) or detraining (CO) (P2), and at end of the following spring season (P3). Isokinetic eccentric and concentric strength was measured in a Kincom. Explosive strength was determined as the contractile Rate of Force Development (RFD) in maximal isometric contraction. Sprint, countermovement jump, and kicking performance were measured. Histochemical analyses were performed to identify fibre type composition and fibre area (type I, IIA and IIX). Non-parametric tests were used for statistical analyses. RESULTS: At P2, the HRT group increased maximal eccentric quadriceps muscle strength and RFD (p < 0.05). A significant decrease in RFD of the hamstrings was observed in the CO group (p < 0.05). At P2, an increase in percentage of type IIA fibres with a corresponding decrease in type IIX fibres were observed for the HRT group (p < 0.05). Fibre area of type IIA and IIX increased in the HRT group, and the fibre area of type IIX decreased in the CO group (p < 0.05). The HRT group improved jump, sprint and kicking performance significantly at P3. CONCLUSIONS: Heavy resistance strength training induced significant increases in maximal eccentric and explosive quadriceps strength. Soccer performance improved only when resistance training was followed by a period of soccer training. Strength increases were accompanied by fibre type transformation from IIX towards IIA and hypertrophy of type IIA and IIX muscle fibres. 12 weeks of detraining induced a significant decrease in RFD of the hamstrings in the CO group. A decrease in RFD of the hamstrings could be a potential risk factor for knee injury in fast and explosive movements.

Understanding muscle coordination of the human leg with dynamical simulations

Muscles coordinate multijoint motion by generating forces that cause reaction forces throughout the body. Thus, a muscle can redistribute existing segmental energy by accelerating some segments and decelerating others. In the process, a muscle may also produce or absorb energy, in which case its summed energetic effect on the segments is positive or negative, respectively. This Borelli Lecture shows how dynamical simulations derived from musculoskeletal models reveal muscle-induced segmental energy redistribution and muscle co-functions and synergies. Synergy occurs when co-excited muscles distribute segmental energy differently to execute the motor task. In maximum height jumping, high vertical velocity at lift-off occurs desirably at full body extension because biarticular leg muscles redistribute the energy produced by the uniarticular leg muscles. In pedaling, synergistic ankle plantarflexor force generation during leg extension allows the high energy produced by the uniarticular hip and knee extensors to be delivered to the crank. An analogous less-powerful flexor synergy exists during leg flexion. Hamstrings reduce crank deceleration during the leg extension-to-flexion transition by not only producing energy but delivering it to the crank through its contribution to the tangential (accelerating) crank force, though this hamstrings function occurs at the opposite (flexion-extension) transition when pedaling backwards. In walking, the eccentric quadriceps activity in early stance not only decelerates the leg but also accelerates the trunk. In mid-stance, the uni- and biarticular plantarflexors, by having opposite segmental energetic effects, act in synergy to support the whole body, so segmental potential and kinetic energy exchange can occur. To conclude, the extraction of unmeasurable variables from dynamical simulations emulating task kinematics, kinetics, and EMGs shows how the production of force and energy by individual muscles contribute to the energy flow among the individual segments during task execution.

Differences in activation patterns between eccentric and concentric quadriceps contractions

Previous studies analysing electromyograms (EMGs) from indwelling electrodes have indicated that fast-twitch motor units are selectively recruited for low-intensity eccentric contractions. The aim of this study was to compare the frequency content of surface EMGs from quadriceps muscles during eccentric and concentric contractions at various contraction intensities. Electromyograms were recorded from the rectus femoris, vastus lateralis and vastus medialis muscles of 10 men during isokinetic (1.05 rad·s -1) eccentric and concentric knee extension contractions at 25%, 50%, 75% and 100% of maximal voluntary contraction (MVC) for each contraction mode. Additionally, isometric contractions (70°) were performed at each intensity. The mean frequency and root mean square (RMS) of the surface EMG were computed. Mean frequency was higher for eccentric than concentric contractions at 25% (P ≪ 0.01), 50% (P ≪ 0.01) and 75% (P ≪ 0.05) but not at 100% MVC. It increased with increasing contraction intensity for isometric (P ≪ 0.001) and concentric (P ≪ 0.01) contractions but not for eccentric contractions (P = 0.27). The EMG amplitude (RMS) increased with increasing contraction intensity similarly in each contraction mode (P ≪ 0.0001). Higher mean frequencies for eccentric than concentric contractions at submaximal contraction intensities is consistent with more fast-twitch motor units being active during eccentric contractions.

The effect of patellar taping on quadriceps peak torque and perceived pain: a preliminary study

Objective: To investigate the effects of corrective patellar taping on quadriceps peak torque and perceived pain levels of patellofemoral pain syndrome (PFPS) patients, while carrying out maximal quadriceps contractions. Method: Fourteen clinically diagnosed PFPS patients had their eccentric and concentric quadriceps peak torques assessed on an isokinetic dynamometer. This procedure was performed with and without corrective patella taping at the contraction velocities of 60 and 180 degrees per second. Perceived pain levels were assessed using a visual analogue scale. Results: In all subjects patella taping reduced perceived pain levels and improved peak torque during both eccentric and concentric contraction modes and at both testing velocities, these changes were all statistically significant (P<0·01). Perceived pain levels were lower at the higher testing speed, for both taped and un-taped situations. Conclusion: These findings have a number of potential treatment implications. Firstly, the relatively greater decrease in pain at the higher testing velocity would indicate the use of faster speeds when treating PFPS. Secondly, taping of the patella provides a useful adjunct to treatment, especially if the goal of treatment is improvement in quadriceps strength, facilitating greater levels of force generation in the quadriceps.

Strength and Flexibility of the Quadriceps Muscle in Adolescent Athletes with Osgood-Schlatter Disease.

In order to investigate the prevention of Osgood-Schlatter disease (OSD) in adolescent athletes, the strength and flexibility of the quadriceps muscles were examined in 30 adolescent athletes with unilateral OSD and 20 adolescent soccer players as a control. The following three factors were examined: 1) quadriceps strength in concentric and eccentric contraction, 2) quadriceps flexibility, and 3) the laterality of the involved knee. There was no significant difference in quadriceps muscle strength between athletes with OSD and soccer players, while quadriceps muscle flexibility in athletes with OSD was significantly low in comparison with soccer players. Although there was no significant difference in quadriceps muscle strength between the uninvolved and involved sides in our patients with unilateral OSD, the left knee was more prone to be affected than the right knee in adolescent athletes. In the great majority of adolescent athletes, the left knee had a tendency to be a dominant leg which was defined as the take-off leg. Since the dominant leg is susceptible to eccentric quadriceps contraction during rapid deceleration while jumping, landing or running when playing sport, we consider that these factors may play a role in the decrease of the quadriceps muscle flexibility in adolescent athletes with OSD. With regard to the prevention of OSD, stretching exercises to relieve the decrease of the quadriceps muscle flexibility and training to reduce the load on the dominant leg are recommended in adolescent athletes.

Neural inhibition during maximal eccentric and concentric quadriceps contraction: effects of resistance training.

Despite full voluntary effort, neuromuscular activation of the quadriceps femoris muscle appears inhibited during slow concentric and eccentric contractions. Our aim was to compare neuromuscular activation during maximal voluntary concentric and eccentric quadriceps contractions, hypothesizing that inhibition of neuromuscular activation diminishes with resistance training. In 15 men, pretraining electromyographic activity of the quadriceps muscles [vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF)] was 17-36% lower during slow and fast (30 and 240 degrees/s) eccentric and slow concentric contractions compared with fast concentric contractions. After 14 wk of heavy resistance training, neuromuscular inhibition was reduced for VL and VM and was completely removed for RF. Concurrently, electromyographic activity increased 21-52, 22-29, and 16-32% for VL, VM, and RF, respectively. In addition, median power frequency decreased for VL and RF. Eccentric quadriceps strength increased 15-17%, whereas slow and fast concentric strength increased 15 and 8%, respectively. Pre- and posttraining median power frequency did not differ between eccentric and concentric contractions. In conclusion, quadriceps motoneuron activation was lower during maximal voluntary eccentric and slow concentric contractions compared with during fast concentric contraction in untrained subjects, and, after heavy resistance training, this inhibition in neuromuscular activation was reduced.

The relationship between functional capacity, muscle size and strength in chronic ACL deficient and ACL reconstructed individuals

Aim: The aim of this study was to assess the relationship between the quadriceps muscle atrophy and strength deficits caused by chronic ACL deficiency, and to ascertain whether these deficits were rectified in subjects who had undergone ACL reconstruction.Methods: Thirteen ACL deficient subjects (ACLD) and eight subjects who had undergone ACL reconstruction (ACLR) participated in the study. Functional capacity, lean thigh volume (LTV), and isokinetic peak torque of the quadriceps and hamstrings muscles were assessed.Results: The ACLD group had a significantly lower score for episodes of giving way compared to the ACLR group (7.4 +/- 3.8 vs. 18.0 +/- 3.7; p &lt; 0.01) and a lower score for inability to perform jumping/twisting activities (1.8 +/- 0.8 vs. 3.6 +/- 1.1; p &lt;0.01; ACLD vs. ACLR) suggesting decreased functional capacity. However, there was no significant difference between the ACLD group and ACLR group for LTV differences (416.0 +/- 276.5 vs. 238.3 +/- 224.4 cc) and quadriceps eccentric peak torque differences (38.1 +/- 13.7 vs. 23.7 +/- 18.3 Nm) between involved and uninvolved limbs. The relationship between LTV and quadriceps isokinetic peak torque was r = 0.59 (p &lt; 0.05) for the ACLD group and r = 0.50 (NS) for the ACLR group.Conclusion: Quadriceps strength deficits are present in ACL deficient subjects, particularly during eccentric contractions. ACL reconstruction improved subjective function and reduced the episodes of giving way, but did not prevent eccentric quadriceps muscle weakness. A low correlation exists between reported function and LTV and eccentric peak torque activity, and between LTV and eccentric peak torque in both ACLD and ACLR groups. These findings suggest that factors other than muscle atrophy are responsible for the functional changes described, in ACL deficient and. ACL reconstructed groups.

Eccentric and concentric isokinetic moment characteristics in the quadriceps and hamstrings of the chronic isolated posterior cruciate ligament injured knee.

OBJECTIVE: Functional strength deficits associated with chronic isolated posterior cruciate ligament (PCL) insufficiency have received limited attention in the literature. The purpose of this study was to determine the eccentric...

Anterior tibial translation during eccentric, isokinetic quadriceps work in healthy subjects.

The effect of increasing isokinetic, eccentric quadriceps torques on sagittal translation of the tibia was examined in six healthy volunteers and compared to the translation at 20 degrees of knee flexion during a drawer test with 90 N force. The tibial translation increased in a linear fashion with a mean of 0.5 mm per 20% torque increase. In 20 degrees of knee flexion, 10% of eccentric quadriceps peak torque consumed 80% of the anterior tibial translation induced by the 90 N Lachman test while eccentric quadriceps peak torque utilized 100% of the translation at the same test. The in vivo relation between muscle force and tibial translation is of importance in the treatment of patients with injury to the cruciate ligaments. The results indicate that an already low eccentric quadriceps torque causes a tibial translation that reaches the limit of the passive knee joint displacement where strain is assumed to develop in the anterior cruciate ligament. Already low eccentric quadriceps torque levels may therefore be harmful during rehabilitation after anterior cruciate ligament surgery.

Unilateral lower limb injury: Its long-term effects on quadriceps, hamstring, and plantarflexor muscle strength

Objective: To ascertain if long-term deficits in quadriceps, hamstring, and plantarflexor muscle strength remain after unilateral lower-limb musculoskeletal injury and to quantify whether improvements in performance continue once a subject concludes rehabilitation and returns to everyday activities. The relation between the size of decrement and limb dominance, type of injury, and time since injury was also considered. Design: Isometric and/or dynamic muscle strength of both legs was measured (using the KinCom 500H isokinetic dynamometer) in 48 subjects. Setting: A physiological laboratory at Brunel University. Patients: Patients were recruited locally via a district general hospital, sports injury clinic, and university. Main Outcome Measures: Muscle strength in the injured limb, reported as a percentage of muscle strength in the uninjured limb. It was assumed that the preinjury state of the injured limb was similar to that of the uninjured limb. Results: Decrements were seen in mean isometric and peak isometric, concentric, and eccentric quadriceps activity ( p < .0001) and isometric plantarflexor activity ( p < .05) in the injured limb, with the type of injury influencing the size of the decrement. Minimal difference was found in the hamstring muscles. Conclusions: The decrements in performance in the quadriceps muscle imply that full recovery (as defined by the preinjury state) is frequently not achieved and stress the need for accurate, objective assessment of muscle strength and further investigation into the nature and duration of rehabilitation after musculoskeletal injury.

Effect of visual feedback and verbal encouragement on eccentric quadriceps and hamstrings peak torque

Biofeedback may be a valuable tool in the rehabilitation of musculoskeletal injury whenever a maximal contraction is desired. The purpose of this study was to investigate the effect of visual feedback (VF) and verbal encouragement (VE) on eccentric quadriceps and hamstrings peak torque of males and females. Fifteen males and 15 females performed eccentric knee flexion/extension at 60°/s on the Biodex B‐2000. Four data collection sessions included one of the following randomly ordered conditions: VF via a bar graph display, VE via a tape recording, VF and VE together, and a control situation (no feedback). Analyses of variance with repeated measured and Tukey post‐hoc tests revealed a significant difference in the results with regard to gender regardless of condition and a significant difference with regard to condition regardless of gender. Males generated more eccentric peak torque than females. VF and combined VF and VE resulted in a higher peak torque value than VE alone and the control condition for both males and females, as well as for quadricep and hamstring muscles.

Correlation between contractile strength and myosin heavy chain isoform composition in human skeletal muscle.

The purpose of this study was to investigate the relationship between myosin heavy chain (MHC) composition and maximal contraction strength of the human quadriceps femoris muscle. Muscle biopsies were obtained from m. vastus lateralis in your highly physical active males (N = 7). The MHC composition of muscle homogenates was determined by electrophoresis techniques (SDS-PAGE). Isokinetic peak torque and constant-angle torque (50 degrees knee flexion) were obtained during slow (30 degrees.s-1), medium (120 degrees.s-1), and fast (240 degrees.s-1) maximal concentric and eccentric quadriceps contractions and expressed relative to muscle volume. The percentage of MHC II in the quadriceps muscle was positively correlated (rs = 0.61-0.93; P < 0.05-0.01) to maximal concentric quadriceps strength obtained at medium to high knee angular velocity. In contrast, no consistent pattern of correlation was observed for maximal eccentric quadriceps strength. The relationship observed between muscular MHC composition and maximal contractile strength is suggested to appear as a consequence of MHC -related differences in contractile force-velocity characteristics and/or contractile Rate of Force Development (RFD).

NEURAL INHIBITION DURING ECCENTRIC AND CONCENTRIC QUADRICEPS CONTRACTION: EFFECTS OF RESISTANCE TRAINING

1178 The aim of this study was to examine the degree of neural inhibition during maximal volitional quadriceps activation, hypothesizing a diminished inhibition after resistance training. Quadriceps EMG and Moment of Force(KinCom) were obtained (1 kHz) during maximal isokinetic knee extensions in young sedentary males (n=15) pre and post 12 wks of heavy resistance training(36 sessions). Slow (30 °·s-1) and fast (240°·s-1) concentric and eccentric quadriceps contractions were tested between 90 ° and 10 ° knee joint angle (0 °=full extension). EMG of the lateral and medial vastii (VL,VM) and rectus femoris(RF) were rectified and smoothed by zero-lag, 4th order Butterworth filter. Subsequently, the average EMG between 30 ° and 70 ° joint angle was computed (iEMG divided by integration time). Prior to training EMG was lower(p<0.0001) in slow concentric, eccentric (30CON, 30ECC) and fast eccentric contraction (240ECC) compared to fast concentric contraction (240CON), indicating significant neural inhibition to appear. To quantify the degree of inhibition, EMG at 30CON, 30ECC, 240ECC were expressed relative to EMG obtained at 240CON: TableTableIn conclusion, substantial neural inhibition was observed for the quadriceps muscle. Post training this inhibition was reduced (VL,VM) or even completely removed (RF).

A new concept for isokinetic hamstring: quadriceps muscle strength ratio.

Conventionally, the hamstring:quadriceps strength ratio is calculated by dividing the maximal knee flexor (hamstring) moment by the maximal knee extensor (quadriceps) moment measured at identical angular velocity and contraction mode. The agonist-antagonist strength relationship for knee extension and flexion may, however, be better described by the more functional ratios of eccentric hamstring to concentric quadriceps moments (extension), and concentric hamstring to eccentric quadriceps moments (flexion). We compared functional and conventional isokinetic hamstring: quadriceps strength ratios and examined their relation to knee joint angle and joint angular velocity. Peak and angle-specific (50 degrees, 40 degrees, and 30 degrees of knee flexion) moments were determined during maximal concentric and eccentric muscle contractions (10 degrees to 90 degrees of motion; 30 and 240 deg/sec). Across movement speeds and contraction modes the functional ratios for different moments varied between 0.3 and 1.0 (peak and 50 degrees), 0.4 and 1.1 (40 degrees), and 0.4 and 1.4 (30 degrees). In contrast, conventional hamstring:quadriceps ratios were 0.5 to 0.6 based on peak and 50 degrees moments, 0.6 to 0.7 based on 40 degrees moment, and 0.6 to 0.8 based on 30 degrees moment. The functional hamstring:quadriceps ratio for fast knee extension yielded a 1:1 relationship, which increased with extended knee joint position, indicating a significant capacity of the hamstring muscles to provide dynamic knee joint stability in these conditions. The evaluation of knee joint function by use of isokinetic dynamometry should comprise data on functional and conventional hamstring:quadriceps ratios as well as data on absolute muscle strength.

Isokinetic Muscle Strength and Capacity for Muscular Knee Joint Stabilization in Elite Sailors

In the present study isokinetic dynamometry was used to evaluate the capacity for dynamic knee joint stabilization via muscle contraction in elite sailors (15 males, SM; 6 females, SF) compared to a group of matched controls (8 males, CM). Maximal concentric, eccentric and isometric moment of force (peak moment and moment at 50 degree knee flexion) was obtained for the knee extensors (quadriceps) and flexors (hamstrings) during isokinetic knee joint movement at angular velocities 0, 30, 120 and 180 degrees x s(-1). High levels of eccentric knee extension strength were observed for the elite sailors compared to the controls (p < 0.05). Based on peak moment and 50 degree moment, respectively, conventional hamstring/quadriceps (H/Q) strength ratio (+/-SD) ranged from 0.37+/-0.06 to 0.54+/-0.06 and from 0.42+/-0.07 to 0.57+/-0.10 across groups, speed and contraction mode. The female elite sailors displayed lower (p<0.05) concentric H/Q ratios at 120 and 180 degrees x s(-1) compared to the controls (0.41-0.45 vs. 0.51-0.56, respectively). The ratio of eccentric hamstring to concentric quadriceps strength (H/Q for extension) or concentric hamstring to eccentric quadriceps strength (H/Q for flexion) may provide a more functional estimate of the capacity for muscular knee joint stabilization (1). Based on peak moment and 50 degree moment, respectively, this "functional" H/Q ratio ranged from 0.24+/-0.03 and 0.25+/-0.02 for knee flexion at 180 degrees x s(-1) to 0.97+/-0.17 and 0.88+/-0.12 for knee extension at 180 degrees x s(-1) among the three groups. Comparable levels of "functional" H/Q ratio were observed (p>0.05) for fast knee extension in the elite sailors (SF:0.81-0.97, SM: 0.88-0.95) and the male controls (CM: 0.80-0.84). In conclusion, a "functional" H/Q ratio of 0.8-1.0 observed for all subjects indicated a significant functional capacity of the hamstring muscles for providing muscular stability at the knee joint in fast knee extension. A significant potential for muscular knee joint stabilization appeared for the elite sailors despite their high maximal quadriceps strength and partially lower (SF) conventional H/Q ratios.

Fatigue after eccentric quadriceps femoris work produces earlier gastrocnemius and delayed quadriceps femoris activation during crossover cutting among normal athletic women.

Athletic women are at greater risk of anterior cruciate ligament (ACL) injury than men. Twenty, healthy, athletic women were evaluated for the effect of preferred stance limb isokinetic quadriceps femoris and hamstring fatigue from eccentric work compared with controls on the activation onset of vastus medialis, rectus femoris, vastus lateralis, the medial hamstrings, biceps femoris, and gastrocnemius muscles. Following 3 weeks of crossover cut training, subjects were tested for fatigue effects (5 subjects/week, 3 conditions, 1 condition/day, order effect controlled) on muscle activation onsets prior to crossover cut landing heelstrike (mixed model, ANOVA, P < 0.05). Fatigue from eccentric quadriceps femoris work produced delayed vastus medialis (P = 0.03), rectus femoris (P = 0.007), and vastus lateralis (P = 0.03) activation onsets compared with control, but did not differ compared to hamstring fatigue. Neither hamstring nor quadriceps femoris fatigue produced differences (P > 0.05) in medial hamstring or biceps femoris activation onsets compared to control. Quadriceps femoris fatigue from eccentric work produced earlier gastrocnemius activation onsets (P = 0.048) than control, but did not differ for hamstring fatigue. The gastrocnemius appears to provide synergistic and compensatory dynamic knee stabilization in closed kinetic chain function during quadriceps femoris fatigue. This finding in a normal group at high risk of ACL injury while performing a maneuver with a high ACL injury risk supports gastrocnemius inclusion in knee rehabilitation and conditioning programs and suggests the need for comparative evaluations of knee injured/reconstructed subjects.

The Effect of Quadriceps Femoris, Hamstring, and Placebo Eccentric Fatigue on Knee and Ankle Dynamics During Crossover Cutting

This study attempted to determine the effect of eccentric quadriceps femoris, hamstring, and placebo fatigue on stance limb dynamics during the plant-and-cut phase of a crossover cut. Twenty female college students (task trained) were tested. Hamstring fatigue resulted in decreased peak impact knee flexion moments (p < or = .01), increased internal tibial rotation at peak knee flexion (p < or = .05), and decreased peak ankle dorisflexion (p < or = .05). Quadriceps fatigue resulted in increased peak ankle dorsiflexion moments (p < .01), decreased peak posterior braking forces (p < or .01), decreased peak knee extension moments (p < or = .01), delayed peak knee flexion (p < or = .01), delayed peak propulsive forces (p < .01), and delayed subtalar peak inversion moments (p < or = .05). Fatigue of either muscle group produced earlier peak ankle plantar flexion moments (p < = .05) and decreased peak propulsive knee flexion moments (p < or = .05). Variables requiring further study (p < or = .1) provide discussion data. Soleus, gastrocnemius, tibialis anterior, and deep posterior compartment calf muscles serve as dynamic impact force attenuators, compensating for fatigued proximal muscles.

Anterior tibial translation related to isokinetic concentric quadriceps torques

A complete rupture of the anterior cruciate ligament (ACL) results in static and often in functional instability. After an ACL-injury, most patients have to decrease their activity level, while some can cope with their injury and manage to keep a high activity level. A better tmderstanding of the influence of muscle activation and external load on the non-injured and injured knee, but also of the adaptive motion strategies employed by the patients with an unstable knee, is of importance for the construction of rehabilitation programs.The general purpose of this thesis was to study certain knee motions during activities focused on rehabilitation, in individuals with anterior cmciate ligament injury and uninjured controls. The sagittal tibial translation and knee flexion angle were registered during motion with the CA-4000 computerized electrogoniometer and EMG was used for analysis of muscle activity. The injured knee had increased static laxity compared to the contralateral non-injured knee and the non-impaired group.The amount of tibial translation increased with increased quadriceps torque during nonweight bearing activities (isokinetic and isotonic contractions). In the non-injured knees, the restraining mechanism was engaged above 50% of isokinetic concentric quadriceps torque and during the eccentric contractions already at low quadriceps torques (<10% of maximum). The motion pattern was similar in the injured knees and the amount of individual translation was larger during the eccentric contractions, compared to the non-injured knees.During weight bearing, tibia translated anteriorly and remained in that position. In the non-injured knee, different loads and performance of weight bearing activities produced different amount of translation. Level walking and squat with the center of gravity behind the feet produced somewhat smaller amount of translations, while other weight bearing activities produced similar amount of translation compared to the non-weight bearing isotonic knee extension. In the injured knee, all weight bearing activities produced similar amount of translation, smaller compared to the non-weight bearing isotonic knee extension.Quadriceps - hamstrings co-activation was not present during non-weight bearing quadriceps dominant activities and therefore, it was not shown to be a factor limiting anterior tibial translation. Also, during the weight bearing activities, hamstrings eo-contraction could not limit the anterior tibial translation. Quadriceps and gastrocnemius seems to work synergistically to stabilize the knee by maintaining an anterior position of tibia.In the injured knee, isokinetic concentric quadriceps contraction below 50% of maximum torque produced the smallest amount of tibial translation. Weight bearing exercises produced similar ammmt of translation despite of load and performance, indicating that when level walking is allowed after an injury, other weight bearing activities can be performed without increasing the amount of translation. Eccentric isokinetic quadriceps contractions above 50% of maximum torque and isotonic quadriceps exercise with and without weights at flexion angles less that 40°, should be avoided in order protect the knee joint.

Effect of cold treatment on the concentric and eccentric torque-velocity relationship of the quadriceps femoris

This study examined the effect of cold treatment on the force-velocity relationship of the quadriceps muscle of 16 athletes. Each subject performed three maximal concentric and eccentric quadriceps contractions on the Kin-Com at 25, 50, 75, 100, 125, 150, 175 and 2000s -I. On one of two testing sessions, subjects received a 20 min ice application prior to testing, and for the remaining session, no ice was applied. The results revealed no significant change in the torque-velocity relationship. A trend analysis revealed linear relationships for the concentric ice [F 0,15) = 82.23] and no ice [F 0,15) = 44.86] conditions as well as for the eccentric ice [F 0,15) = 38.58] and no ice [F (1,15) = 26.40] conditions. There were no significant differences between the concentric ice and no ice means at any velocity, but peak torque at 2000s -I was significantly different from peak torque at 25-1000s -I. For eccentric contractions there was a difference between ice and no ice means, with an increase of 20% and 16% for the ice condition at 175 and 2000s -I, respectively. For the eccentric ice conditions across velocities, the PT at 2000s -I was significantly different from the PT at 125-2000s -I. This suggests that the application of ice will not decrease strength but may in fact result in an increase in eccentric strength.

The Influence of Aging on Muscle Strength and Muscle Fiber Characteristics With Special Reference to Eccentric Strength

It is well established that aging seriously reduces isometric and concentric muscle strength due to atrophy, deterioration of mechanical properties, and motor unit loss. However, there is limited information on the impact of aging on eccentric strength despite the fact that such forces play an equally important role during daily activities. The purpose of this study was to examine the influence of aging on three expressions of muscle strength (isometric, concentric, and eccentric) in relation to muscle fiber characteristics, with special emphasis on eccentric force. Sedentary but healthy men (age range 18-80 years, n = 60) and women (20-74 years, n = 30) were tested for maximal effort isometric, concentric, and eccentric (1.05, 2.09, 3.14 rads.s-1) quadriceps strength, body composition, and muscle fiber characteristics of the vastus lateralis (men only). There was a significant (p < .05) approximately 30 N per decade decline in isometric and concentric forces, but only 9 N per decade reduction in eccentric strength. There was a significant reduction in Type II muscle fiber area with aging (p < .05). Isometric, eccentric, and concentric force correlated r = .33, r = .32 (p < .05), and r = .12 (p > .05) with Type II muscle fiber area, respectively. The correlation between age and fat-free mass/force ratio ranged from r = .39 to .43 in men and r = .27 to .50 in women. The data suggest a relative preservation of eccentric strength with aging in men and women that seems to be independent of muscle mass or muscle fiber type or size.