Evidence of neuromuscular fatigue after prolonged cycling exercise

PURPOSE: The purpose of this study was to analyze the effects of prolonged cycling exercise on metabolic, neuromuscular, and biomechanical parameters. METHODS: Eight well-trained male cyclists or triathletes performed a 2-h cycling exercise at a power output corresponding to 65% of their maximal aerobic power. Maximal concentric (CON; 60, 120, 240 degrees x s(-1)), isometric (ISO; 0 degrees s(-1)), and eccentric (ECC; -120, -60 degrees x s(-1)) contractions, electromyographic (EMG) activity of vastus lateralis (VL) and vastus medialis (VM) muscles were recorded before and after the exercise. Neural (M-wave) and contractile (isometric muscular twitch) parameters of quadriceps muscle were also analyzed using electrical stimulation techniques. RESULTS: Oxygen uptake (VO2), minute ventilation (VE), and heart rate (HR) significantly increased (P < 0.01) during the 2-h by, respectively, 9.6%, 17.7%, and 12.7%, whereas pedaling rate significantly decreased (P < 0.01) by 21% (from 87 to 69 rpm). Reductions in muscular peak torque were quite similar during CON, ISO, and ECC contractions, ranging from 11 to 15%. M-wave duration significantly increased (P < 0.05) postexercise in both VL and VM, whereas maximal amplitude and total area decreased (VM: P < 0.05, VL: NS). Significant decreases in maximal twitch tension (P < 0.01), total area of mechanical response (P < 0.01), and maximal rate of twitch tension development (P < 0.05) were found postexercise. CONCLUSIONS: A reduction in leg muscular capacity after prolonged cycling exercise resulted from both reduced neural input to the muscles and a failure of peripheral contractile mechanisms. Several hypothesis are proposed to explain a decrease in pedaling rate during the 2-h cycling with a constancy of power output and an increase in energy cost.     

EMG threshold determination in eight lower limb muscles during cycling exercise: a pilot study

The first aim of this study was to verify the occurrence of the EMG threshold (EMG (Th)) in each of eight lower limb muscles (vastus lateralis [VL], vatus medialis [VM], rectus femoris [RF], semimembranosus [SM], biceps femoris [BF], gastrocnemius lateralis [GL] and medialis [GM], and tibialis anterior [TA]) during incremental cycling exercise. The second aim was to investigate the test-retest reproducibility of the EMG (Th) occurrence. Six sedentary male subjects (27 +/- 1 years) performed the same incremental cycling test until exhausted, (workload increments of 25 W/min starting at 100 W) twice. During the tests, the EMG Root Mean Square (RMS) response was studied in the aforementioned muscles. The EMG (Th) was detected mathematically from the RMS vs. workload relationship. All the subjects showed an EMG (Th) in the VL muscle, and the response was reliable in both tests (246 +/- 33 W and 254 +/- 33 W for the first and second test, respectively; coefficient of variation: 9.6 %, standard error of measurement: 28.9). However, few of them showed an EMG (Th) in the other muscles, especially in RF, SM or GM. When present, the EMG (Th) occurred at 75 - 80 % of the peak power output obtained during the tests. Our results suggest that EMG (Th) determination can be used as a reliable method for studying neuromuscular adjustments in the VL of untrained individuals, but not in other lower limb muscles.     

The effects of a prolonged running exercise on strength characteristics

The aim of this study was to examine concentric, isometric, and eccentric strength reductions in the quadriceps muscle following a prolonged running exercise. Before and after a 2 h run (28.4+/-1.4 km) peak torque (PT) of the knee extensors at angular velocities of -120, -90, -60, 0, 60, 120, 180, 240 degrees x s(-1) using an isokinetic dynamometer, electromyographic (EMG) activity of the vastus lateralis (VL) and vastus medialis (VM) muscles and height of a counter movement jump were recorded in twelve well-trained triathletes. Counter movement jump performances decreased by 10% and PT values were all significantly lower (p < 0.01) at each angular velocity following the run. The torque loss was significantly (p < 0.01) greater under eccentric contractions (from 18 to 21%) than under concentric ones (from 11 to 14%). EMG activity (RMS) was lower in both VL and VM muscles after the 2 h run but no difference existed in RMS losses between concentric and eccentric contractions. The present results demonstrate that 1) a prolonged running exercise more greatly affects eccentric force production in the quadriceps muscle, and 2) this specificity seems to be due to an impairment of the muscular contractile mechanism rather than a modification to the neural input.     

Using surface electrodes for the evaluation of the rectus femoris, vastus medialis and vastus lateralis muscles in children with cerebral palsy

The purpose of this study was to determine if surface electrodes are adequate in the determination of the activity patterns of the rectus femoris, vastus medialis and vastus lateralis in children with cerebral palsy (CP). Ninety patients with a diagnosis of CP underwent electromyography (EMG) testing. Surface electrodes were placed on the rectus femoris (RF), hamstrings, vastus medialis (VM) and vastus lateralis (VL). Muscle isolation tests revealed no cross-talk of the RF muscle on the vastii electrodes in any subject indicating surface EMG is sufficient for testing RF, VM and VL function in children. Muscle activation patterns during gait showed that the RF and not the VM or VL was active in mid-swing in the majority of cases.     

Gender, muscle, and velocity comparisons of mechanomyographic and electromyographic responses during isokinetic muscle actions

The purpose of this study was to examine the responses of peak torque (PT), mean power output (MP), mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) in males and females during maximal, concentric isokinetic muscle actions. Subjects performed maximal leg extensions at 60 degrees s(-1), 120 degrees s(-1), 180 degrees s(-1), 240 degrees s(-1), 300 degrees s(-1), 360 degrees s(-1), 420 degrees s(-1), and 480 degrees s(-1). No gender differences were observed, but there were muscle-specific differences for the patterns of MMG MPF, EMG amplitude, and EMG MPF. The MP and MMG amplitude increased to 180-240 degrees s(-1), plateaued, and then decreased to 480 degrees s(-1). MMG MPF for the VL and VM remained unchanged to 300 degrees s(-1), but then increased to 480 degrees s(-1). The EMG amplitude for the RF and EMG MPF for the VL decreased across velocity. Overall, these findings indicated that there were muscle-specific, velocity-related differences in the associations among motor control strategies (EMG amplitude and MPF) and the mechanical aspects of isokinetic muscular activity (MMG amplitude and MPF).     

Electromyostimulation training effects on neural drive and muscle architecture

PURPOSE: The purpose of the study was to investigate the effect of 4 and 8 wk of electromyostimulation (EMS) training on both muscular and neural adaptations of the knee extensor muscles. METHODS: Twenty males were divided into the electrostimulated group (EG, N = 12) and the control group (CG, N = 8). The training program consisted of 32 sessions of isometric EMS over an 8-wk period. All subjects were tested at baseline (B) and retested after 4 (WK4) and 8 (WK8) wk of EMS training. The EMG activity and muscle activation obtained under maximal voluntary contractions (MVC) was used to assess neural adaptations. Torque and EMG responses obtained under electrically evoked contractions, muscle anatomical cross-sectional area (ACSA), and vastus lateralis (VL) pennation angle, both measured by ultrasonography imaging, were examined to analyze muscular changes. RESULTS: At WK8, knee extensor MVC significantly increased by 27% (P < 0.001) and was accompanied by an increase in muscle activation (+6%, P < 0.01), quadriceps muscle ACSA (+6%, P < 0.001), and VL pennation angle (+14%, P < 0.001). A significant increase in normalized EMG activity of both VL and vastus medialis (VM) muscles (+69 and +39%, respectively, P < 0.001) but not of rectus femoris (RF) muscle was also found at WK8. The ACSA of the VL, VM, and vastus intermedius muscles significantly increased at WK8 (5-8%, P < 0.001) but not at WK4, whereas no changes occurred in the RF muscle. CONCLUSION: We concluded that the voluntary torque gains obtained after EMS training could be attributed to both muscular and neural adaptations. Both changes selectively involved the monoarticular vastii muscles.     

Effect of knee joint angle on neuromuscular activation of the vastus intermedius muscle during isometric contraction

The purpose of this study was to compare the relationship between surface electromyography (EMG) and knee joint angle of the vastus intermedius muscle (VI) with the synergistic muscles in the quadriceps femoris (QF) muscle group. Fourteen healthy men performed maximal voluntary contractions during isometric knee extension at four knee joint angles from 90°, 115°, 140°, and 165° (180° being full extension). During the contractions, surface EMG was recorded at four muscle components of the QF muscle group: the VI, vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles. The root mean square of the surface EMG at each knee joint angle was calculated and normalized by that at a knee joint angle of 90° for individual muscles. The normalized RMS of the VI muscle was significantly lower than those of the VL and RF muscles at the knee joint angles of 115° and 165° and those of the VL, VM, and RF muscles at the knee joint angle of 140° (P<0.05). The present results suggest that the neuromuscular activation of the VI muscle is regulated in a manner different from the alteration of the knee joint angle compared with other muscle components of the QF muscle group.     

Effect of high-intensity intermittent cycling sprints on neuromuscular activity

High-intensity intermittent sprints induce changes in metabolic and mechanical parameters. However, very few data are available about electrical manifestations of muscle fatigue following such sprints. In this study, quadriceps electromyographic (EMG) responses to repeated all-out exercise bouts of short duration were assessed from maximal voluntary isometric contractions (MVC) performed before and after sprints. Twelve men performed ten 6-s maximal cycling sprints, separated by 30-s rest. The MVC were performed pre-sprints ( pre), post-sprints ( post), and 5 min post-sprints ( post5). Values of root-mean-square (RMS) and median frequency (MF) of vastus lateralis (VL) and vastus medialis (VM) were recorded during each MVC. During sprints, PPO decreased significantly in sprints 8, 9, and 10, compared to sprint 1 (- 8 %, - 10 %, and - 11 %, respectively, p < 0.05). Significant decrements were found in MVC post (- 13 %, p < 0.05) and MVC post5 (- 10.5 %, p < 0.05) compared to MVC pre. The RMS value of VL muscle increased significantly after sprints (RMS pre vs. RMS post: + 15 %, p < 0.05). Values of MF decreased significantly in both VL and VM after sprints. In conclusion, our results indicate that the increase in quadriceps EMG amplitude following high-intensity intermittent short sprints was not sufficient to maintain the required force output. The concomitant decrease in frequency components would suggest a modification in the pattern of muscle fiber recruitment, and a decrease in conduction velocity of active fibers.     

Heterogeneous recruitment of quadriceps muscle portions and fibre types during moderate intensity knee-extensor exercise: effect of thigh occlusion

The involvement of quadriceps femoris muscle portions and fibre type recruitment was studied during submaximal knee-extensor exercise without and with thigh occlusion (OCC) and compared with responses during intense exercise. Six healthy male subjects performed 90-s of moderate exercise without (MOD; 29±4 W) and with thigh OCC, and moderate exercise followed by 90-s of intense exercise (HI; 65±8 W). Temperatures were continuously measured in m. vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) and successive muscle biopsies were obtained from VL. During MOD, muscle temperature increase (Δ T _m) in RF was 0.52±0.09 °C, which was 57% and 73% higher ( P <0.05) than in VL and VM, respectively. During OCC, Δ T _m in RF was 0.39±0.05 °C, which was not different from VM but 54% higher ( P <0.05) than in VL. After MOD, muscle CP in slow twitch (ST) and fast twitch (FT) fibres was 81% and 91% of resting levels, respectively, with lower ( P <0.05) values after OCC (15% and 22%) and HI (24% and 13%). After MOD, OCC and HI, a total of 48%, 93% and 96% of the ST fibres had CP levels below mean-1 SD, respectively, with corresponding values for FT fibres being 41%, 89% and 100%, respectively. In conclusion, a heterogeneous recruitment of the quadriceps muscle portions and muscle fibres was observed during submaximal knee-extensor exercise, whereas recruitment pattern was homogenous during intense exercise. Thigh OCC caused an altered recruitment of fibres and muscle portions, suggesting a significant afferent response affecting the activation of fibres in the contracting muscles.     

Influence of different racing positions on mechanical and electromyographic patterns during pedalling

The aim of this study was to test the hypothesis that, in comparison with standard postures, aero posture (AP) would modify the coordination of lower limb muscles during pedalling and consequently would influence the pedal force production. Twelve triathletes were asked to pedal at an intensity near the ventilatory threshold (VT+Δ20%) and at an intenisty corresponding to the respiratory compensation point (RCP). For each intensity, subjects were tested under three positions: (1) upright posture (UP), (2) dropped posture (DP), and (3) AP. Gas exchanges, surface electromyography and pedal effective force were continuously recorded. No significant difference was found for the gas-exchange variables among the three positions. Data illustrate a significant increase [ gluteus maximus (GMax), vastus medialis (VM)] and decrease [ rectus femoris (RF)] in electromyography (EMG) activity level in AP compared with UP at RCP. A significant shift forward of the EMG patterns (i.e. later onset of activation) was observed for RF (at VT+Δ20% and RCP), GMax, VL, and VM (at RCP) in AP compared with UP. These EMG changes are closely related to alteration of force profile in AP (higher downstroke positive peak force, lower upstroke negative peak force, and later occurrence of these peaks along the crank cycle).     

Quadriceps EMG/force relationship in knee extension and leg press

PURPOSE: This study compared the relationship between surface electromyographic (EMG) activity and isometric force of m. quadriceps femoris (QF) in the single-joint knee extension (KE) and the multi-joint leg press (LP) exercises. METHODS: Nine healthy men performed unilateral actions at a knee angle of 90 degrees at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC). EMG was measured from m. vastus lateralis (VL), m. vastus medialis (VM), m. rectus femoris (RF), and m. biceps femoris (BF). RESULTS: There were no differences in maximum EMG activity of individual muscles between KE and LP. The QF EMG/force relationship was nonlinear in each exercise modality. VL showed no deviation from linearity in neither exercise, whereas VM and RF did. BF activity increased linearly with increased loads. CONCLUSIONS: The EMG/force relationship of all quadricep muscles studied appears to be similar in isometric multi-joint LP and single-joint KE actions at a knee angle of 90 degrees. This would indicate the strategy of reciprocal force increment among muscles involved is comparable in the two models. Furthermore, these data suggest a nonuniform recruitment pattern among the three superficial QF muscles and surface EMG recordings from VL to be most reliable in predicting force output.     

The effects of ACL injury on lower extremity activation during closed kinetic chain exercise

AIM: Injury to the anterior cruciate ligament (ACL) has been suggested to alter the neuromuscular mechanism in the lower extremity. However, conclusive evidence regarding this occurrence has yet to be established during closed kinetic chain exercise. The purpose of this study was to assess differences in muscle activation during slideboard exercise between non-injured, ACL deficient, and ACL reconstructed individuals. METHODS: Experimental design: comparative study. Setting: research laboratory. Participants: subjects for this study included 10 healthy, non-injured (NI) individuals, 7 uni-lateral ACL deficient (ACLD) individuals, and 6 uni-lateral ACL reconstructed (ACLR) individuals. Interventions: EMG activity was measured from the vastus medialis (VM), vastus lateralis (VL), medial hamstring (MH), lateral hamstring (LH), tibialis anterior (TA), and medial gastrocnemius (MG) muscles during slideboard performance. Measures: EMG for each muscle during each of 6 phases of 1 average slideboard cycle was expressed as a percentage of EMG during a maximal voluntary contraction. RESULTS: The results demonstrated that during slideboard phase I the VM, VL, and TA muscles generated the greatest amount of activity as compared to the other muscles. Vastus medialis muscle activation was found to be significantly higher than the other muscles in the involved/dominant limb, as compared to the non-involved/non-dominant limb during slideboard phase II. During slideboard phases III-VI, tibialis anterior muscle activation was found to be consistently higher than the other muscles, while hamstring muscle activity was consistently the lowest. CONCLUSION: It is concluded that adaptive changes following ACL injury during a dynamic, closed kinetic chain activity such as the slideboard exercise, may be a restoration of a bi-lateral balance in muscle activation.     

Gastrocnemius medialis and vastus lateralis oxygenation during whole-body vibration exercise

PURPOSE: The aim of this study was to investigate the effects of different whole-body vibration (WBV) frequencies on oxygenation of vastus lateralis (VL) and gastrocnemius medialis (GM) muscles during static squatting in sedentary and physically active healthy males. METHODS: Twenty volunteers (age: 24.6 +/- 2.9 yr; body mass: 80.6 +/- 11.8 kg; height: 178.1 +/- 7.6 cm) participated in this study. Ten subjects were sedentary individuals and 10 were athletes practicing different sports. All subjects completed four trials (control, and 30-, 40-, and 50-Hz WBV) in a randomized controlled crossover design. The trials consisted of static squatting on a vibrating platform for a total duration of 110 s. Muscle-oxygenation status was recorded with near-infrared spectroscopy. RESULTS: The data analysis revealed no significant treatment-by-time interactions in tissue-oxygenation index (TOI) or Delta total hemoglobin volume (tHb) in VL and GM muscles. A significant main effect of time in TOI of both VL and GM muscles was identified (P<0.001). VL TOI significantly decreased by 2.8% at 90 s in the control condition and by 3.3% at 110 s in the 30-Hz condition; VL TOI significantly increased by 2.1 and 3.0% at 30 s in the 40- and 50-Hz conditions, respectively. GM TOI significantly decreased by 3.2% at 60 s, by 4.1% at 90 s, and by 4.3% at 110 s in the control condition, and by 5.5% at 110 s in the 30-Hz condition. CONCLUSION: This study showed that WBV exercise with frequencies of 30, 40, and 50 Hz and small amplitudes does not affect muscle oxygenation of VL and GM muscles to a higher degree than a nonvibration condition.     

Determination of thigh muscle stiffness using magnetic resonance elastography

PURPOSE: To measure the elastic properties of the vastus lateralis (VL), vastus medialis (VM), and sartorius (Sr) muscles using magnetic resonance elastography (MRE). MATERIALS AND METHODS: To obtain a normative database of the aforementioned muscles, oblique scan directions were prescribed passing through each muscle. Shear waves were induced into the muscles using pneumatic and mechanical drivers at 90 and 120 Hz, respectively. These drivers were attached to the distal end of the right thigh with the knee flexed at 30 degrees . The foot was placed in a footplate containing MR-compatible load cells to record the force during a contraction (10% and 20% of the maximum voluntary contraction). RESULTS: The shear moduli measured at rest in the VL (N = 12), VM (N = 14), and Sr (N = 13) were 3.73 +/- 0.85 kPa, 3.91 +/- 1.15 kPa, and 7.53 +/- 1.63 kPa, respectively. The stiffness of both vasti increased with the level of contraction, while the stiffness of the Sr remained the same. CONCLUSION: The MRE technique was able to approximate the stiffness of different thigh muscles. Furthermore, the wave length was sensitive to the morphology (unipennate or longitudinal) and fiber composition (type I or II) in each muscle.     

Assessment of magnetic resonance techniques to measure muscle damage 24 h after eccentric exercise

The study examined which of a number of different magnetic resonance (MR) methods were sensitive to detecting muscle damage induced by eccentric exercise. Seventeen healthy, physically active participants, with muscle damage confirmed by non‐MR methods were tested 24 h after performing eccentric exercise. Techniques investigated whether damage could be detected within the quadriceps muscle as a whole, and individually within the rectus femoris, vastus lateralis (VL), vastus medialis (VM), and vastus intermedius (VI). Relative to baseline values, significant changes were seen in leg and muscle cross‐sectional areas and volumes and the resting inorganic phosphate concentration. Significant time effects over all muscles were also seen in the transverse relaxation time (T2) and apparent diffusion coefficient (ADC) values, with individually significant changes seen in the VL, VM, and VI for T2 and in the VI for ADC. A significant correlation was found between muscle volume and the average T2 change (r = 0.59) but not between T2 and ADC or Pi alterations. There were no significant time effects over all muscles for magnetization transfer contrast images, for baseline pH, phosphocreatine (PCr), phosphodiester, or ATP metabolite concentrations or the time constant describing the rate of PCr recovery following exercise.     

A clinical case and anatomical study of the innervation supply of the vastus medialis muscle

The innervation supply to the vastus medialis (VM) muscle, a component of quadriceps femoris (QF), is provided by a branch of the femoral nerve (FN) running along the muscle. The course of the nerve from lumbar roots to the muscle has been described by many researchers. It is known to ride along the femoral vein, artery and saphenous nerve and enter the adductor canal (Hunter's canal), and then to divide into branches that supply vastus medialis and the knee joint. Femoral mononeuropathy is uncommon, and is usually due to compression in the spinal level. Hematoma in the psoas and iliacus muscles, drug abuse, lithotomy position and limb lengthening are the other associated reasons for a mononeuropathy of the femoral nerve. Isolated vastus lateralis (VL) atrophies have been reported by a few authors, suggesting that compression of the nerve and direct violation of the nerve with injections might be the reason for mononeuropathy. Isolated VM atrophy has not been previously reported. The purpose of the study was to identify the anatomical structures around the FN branch which innervates the VM muscle.     

New insights into the function of the vastus medialis with clinical implications

PURPOSE: To investigate the gross anatomy of the distal portion of the quadriceps, and to compare the relative contributions of the vastus medialis oblique (VMO) and vastus lateralis (VL) during dynamic weight-bearing conditions. METHODS: Dissection was carried out on 10 cadavers by a longitudinal incision from the anterior superior iliac spine to the patella and completed with upper and lower transverse cuts to reinvestigate the gross anatomy and innervation patterns of the quadriceps femoris. A biomechanical test of knee kinematics was conducted on 10 healthy male volunteers. Maximal isometric force, squat jump, and drop movement jump exercises were performed on a force plate and filmed using a Saga-3 3D system, and surface EMG activity was recorded for the VMO and the VL. RESULTS: The oblique fibers of the vastus medialis (VM) are not only attached to the medial border of the patella, but they also have a small region of direct continuity with the patellar tendon. Furthermore, VMO fibers in the middle and proximal thirds of the thigh attached to vastus intermedius, whereas distally, the fibers were independent. Both parts of the VM (proximal and distal) had independent motor points. During jumping exercises, the VMO and VL were activated in a coordinated manner in a squat jump using both legs. However, in a single-leg squat jump (which challenged the stability of the knee joint more acutely), VMO activation was higher during landing. CONCLUSION: VMO activity was pronounced during the weight-bearing conditions, with increased medial and lateral knee movements. This suggests that the VM should not be considered simply as a knee extensor or as a muscle whose main role is to maintain normal patellar tracking.     

Whole body vibration does not potentiate the stretch reflex

Whole body vibration (WBV) is theorized to enhance neural potentiation of the stretch reflex. The purpose of this study was to determine if WBV affects the quadriceps reflex from a patellar tendon tap. Subjects were 22 volunteers (age 23 +/- 2 yrs, ht 172.8 +/- 10.8 cm, body mass 68.6 +/- 12.3 kg). The stretch reflex was elicited from the dominant leg pre, post, and 30-min post WBV treatment. A matched control group repeated the procedure without WBV. WBV treatment consisted of 5, 1-min bouts at 26 Hz with a 1-min rest period between bouts while maintaining a standardized squatting position. Two-way ANOVAs were used to detect differences between groups over time for vastus medialis (VM) and vastus lateralis (VL) latency, EMG amplitude, electromechanical delay (EMD), and force output. No group x time interactions were detected for latency (VM; F ((2,40)) = 1.20, p = .313: VL; F ((2,40)) = 0.617, p = .544), EMG mean amplitude (VM; F ((2,40)) = 0.169, p = .845: VL; F ((2,40)) = 0.944, p = .398), EMD (VM; F ((2,40)) = 0.715, p = .495: VL; F ((2,40)) = 1.24, p = .301), or quadriceps force (F ((2,40)) = 1.11, p = .341) A single session WBV treatment does not affect the quadriceps stretch reflex in terms of timing or amplitude.     

Atrophy of thigh muscles after meniscal lesions and arthroscopic partial menisectomy

The purpose of this study was to investigate the atrophic pattern of the muscle groups and their individual muscles in the thigh after meniscal lesions and arthroscopic partial menisectomy. A total of 32 individuals (17 men and 15 women) who underwent arthroscopic knee surgery participated in this study. Their operated and non-operated thighs were scanned by magnetic resonance imaging to determine the volume of the quadriceps (QF), hamstring (HM), and adductors (AD). Compared with the non-operated limb, the volume of the QF was significantly lower in the operated limb; however, no significant difference was observed in the HM and AD. The volume of individual muscles of the QF, i.e. the rectus femoris (RF), vastus lateralis (VL), vastus intermedius (VI), and vastus medialis (VM), in the operated limb was significantly lower than the volume of those in the non-operated limb (P<0.01, all). Although the relative change in the VM was significantly higher than that of the RF (P<0.05), specific atrophy was not found among four individual muscles in the QF. We concluded that meniscal lesions and partial menisectomy induce atrophy in the QF only in the thigh, and that no specific atrophy, e.g. VM, seemed to occur within the individual muscles in the QF.     

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 (T ₂)‐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 60 minutes with −10% slope, 6 km/h velocity, and 20% body mass load carried. At pre‐ and 24‐, 48‐, and 72‐hours post‐exercise, T ₂‐MRI was scanned and T ₂ 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 24‐48 hours after all exercises. T ₂ significantly increased (3%‐9%) at 24‐72 hours after all exercises, with heterogeneities within the muscles found in each exercise. Effect size and peak change of T ₂, 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 T ₂ 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.