The role of cadence on the VO2 slow component in cycling and running in triathletes.

The purpose of this study was to compare the effect of two different types of cyclic severe exercise (running and cycling) on the VO2 slow component. Moreover we examined the influence of cadence of exercise (freely chosen [FF] vs. low frequency [LF]) on the hypothesis that: 1) a stride frequency lower than optimal and 2) a pedalling frequency lower than FF one could induce a larger and/or lower VO2 slow component. Eight triathletes ran and cycled to exhaustion at a work-rate corresponding to the lactate threshold + 50% of the difference between the work-rate associated with VO2max and the lactate threshold (delta 50) at a freely chosen (FF) and low frequency (LF: - 10 % of FF). The time to exhaustion was not significantly different for both types of exercises and both cadences (13 min 39 s, 15 min 43 s, 13 min 32 s, 15 min 05 s for running at FF and LF and cycling at FF and LF, respectively). The amplitude of the VO2 slow component (i.e. difference between VO2 at the last and the 3rd min of the exercise) was significantly smaller during running compared with cycling, but there was no effect of cadence. Consequently, there was no relationship between the magnitude of the VO2 slow component and the time to fatigue for a severe exercise (r = 0.20, p = 0.27). However, time to fatigue was inversely correlated with the blood lactate concentration for both modes of exercise and both cadences (r = - 0.42, p = 0.01). In summary, these data demonstrate that: 1) in subjects well trained for both cycling and running, the amplitude of the VO2 slow component at fatigue was larger in cycling and that it was not significantly influenced by cadence; 2) the VO2 slow component was not correlated with the time to fatigue. If the nature of the linkage between the VO2 slow component and the fatigue process remains unclear, the type of contraction regimen depending on exercise biomechanic characteristics seems to be determinant in the VO2 slow component phenomenon for a same level of training.     

VO2 slow component is independent from critical power

The aim of this study was to determine whether the amplitude of the V˙O (2) slow component was dependent from Critical Power (CP; the slope of the linear time - distance relationship) in individuals matched for V˙O (2) peak. 30 moderately-trained endurance athletes completed a maximal graded exercise test, 2 randomly ordered constant power tests at 90 and 100% of peak power output (PPO), and 2 constant duration test of 6 min at 30% of the difference between CP and PPO. Afterwards, participants were ranked according to their relative CP (%PPO; a direct measure of aerobic endurance). The median third was excluded to form a low aerobic endurance group (LEG) and a high aerobic endurance group (HEG). A t-test revealed no difference between LEG and HEG in peak oxygen consumption, but a large difference in their relative CP (p<0.001, effect size=3.2). A' (2) was similar between groups (626 ± 96 and 512 ± 176 ml, corresponding to 26 ± 4 and 24 ± 8% of end exercise oxygen consumption, respectively; NS) and was not associated with relative CP (r=0.10; NS). These results suggest that increasing CP probably extends the range of exercise intensities over which the V˙O (2) slow component does not develop, but does not decrease the amplitude of this phenomenon once it occurs.     

The slow component of VO2 in professional cyclists

OBJECTIVES: To analyse the slow component of oxygen uptake (VO2) in professional cyclists and to determine whether this phenomenon is due to altered neuromuscular activity, as assessed by surface electromyography (EMG). METHODS: The following variables were measured during 20 minute cycle ergometer tests performed at about 80% of VO2MAX in nine professional road cyclists (mean (SD) age 26 (2) years; VO2max 72.6 (2.2) ml/kg/min): heart rate (HR), gas exchange variables (VO2, ventilation (VE), tidal volume (VT), breathing frequency (fb), ventilatory equivalents for oxygen and carbon dioxide (VE/VO2 and VE/VCO2 respectively), respiratory exchange ratio (RER), and end tidal PO2 and PCO2 (PETO2 and PETCO2 respectively)), blood variables (lactate, pH, and [HCO3-]) and EMG data (root mean from square voltage (rms-EMG) and mean power frequency (MPF)) from the vastus lateralis muscle. RESULTS: The mean magnitude of the slow component (from the end of the third minute to the end of exercise) was 130 (0.04) ml in 17 minutes or 7.6 ml/min. Significant increases from three minute to end of exercise values were found for the following variables: VO2 (p<0.01), HR (p<0.01), VE (p<0.05), fb (p<0.01), VE/VO2 (p<0.05), VE/VCO2 (p<0.01), PETO2 (p<0.05), and blood lactate (p<0.05). In contrast, rms-EMG and MPF showed no change (p>0.05) throughout the exercise tests. CONCLUSIONS: A significant but small VO2 slow component was shown in professional cyclists during constant load heavy exercise. The results suggest that the primary origin of the slow component is not neuromuscular factors in these subjects, at least for exercise intensities up to 80% of VO2MAX.     

Branched-chain amino acids supplementation attenuates the accumulation of blood lactate dehydrogenase during distance running

AIM: We investigated the effect of branched-chain amino acids (BCAA) supplementation on tissue damage during distance running. METHODS: Eight male distance runners (mean +/- standard deviation; age: 20.4+/-1.2 years, body weight: 58.4+/-4.2 kg) participated in a double blinded cross over designed study conducted during training camp. During each intervention period, the subjects were asked to participate in a 25-km run, and the blood BCAA and lactate dehydrogenase (LDH) level, an index of tissue damage, were measured pre- and post-run. Either a drink containing BCAA (0.4% BCAA in a 4% carbohydrate solution) or an iso-calorie placebo drink was provided to the subjects 5 times during the run without any restriction in the volume. RESULTS: The total volume of the drink consumed by the subjects did not differ substantially between the trials: 591+/-188 (2.36 g BCAA) vs 516+/-169 mL in BCAA and placebo trial, respectively. During the run, the blood BCAA concentration was maintained in the BCAA trial. However, the blood BCAA concentration level tended to decrease in the placebo trial (P<0.1). The extent of the blood LDH increase in the BCAA trial was significantly less than that of the placebo trail (48% vs 58%, P<0.05). CONCLUSION: Maintaining the blood BCAA level throughout a long distance run contributes to a reduction in the LDH release and, therefore, the effect of BCAA supplementation is suggested to reduce the degree of muscle damage.     

ACL reconstructed patients with a BPTB graft present an impaired vastus lateralis neuromuscular response during high intensity running

The purpose of the present study was to investigate whether the electromyographic response of the vastus lateralis (VL) muscle in the anterior cruciate ligament (ACL) reconstructed leg is similar to that of the intact contralateral leg and healthy controls, during moderate and high intensity running. Fourteen bone–patellar tendon–bone (BPTB) ACL reconstructed amateur soccer players and fourteen healthy control amateur soccer players volunteered to participate in the study. Electromyographic (EMG) traces from the vastus lateralis (VL) muscle were collected bilaterally, as athletes ran on a treadmill for 10 min on separate occasions, at moderate and high intensity. The dependent variable examined was the EMG amplitude during stance. During the moderate intensity running, EMG amplitude of the VL did not increase with time for any of the tested legs. During the high intensity running, the EMG amplitude of the VL increased significantly with time for the intact (F = 6.747, p = 0.001) and the control leg (F = 4.258, p = 0.008), but remained unchanged for the ACL reconstructed leg. During moderate intensity running, there was no difference in the neuromuscular response of the VL in the reconstructed leg compared to the intact and control leg. High intensity running resulted in an impaired neuromuscular response of the VL in the reconstructed leg compared to the intact and control leg. It seems that potential impairments of the neuromuscular response after ACL reconstruction should be tested under high rather than moderate intensity efforts.     

Time limit and VO2 slow component at intensities corresponding to VO2max in swimmers

The purpose of this study was to measure, in swimming pool conditions and with high level swimmers, the time to exhaustion at the minimum velocity that elicits maximal oxygen consumption (TLim at vVO(2)max), and the corresponding VO(2) slow component (O(2)SC). The vVO(2)max was determined through an intermittent incremental test (n = 15). Forty-eight hours later, TLim was assessed using an all-out swim at vVO(2)max until exhaustion. VO(2) was measured through direct oximetry and the swimming velocity was controlled using a visual light-pacer. Blood lactate concentrations and heart rate values were also measured. Mean VO(2)max for the incremental test was 5.09 +/- 0.53 l/min and the corresponding vVO(2)max was 1.46 +/- 0.06 m/s. Mean TLim value was 260.20 +/- 60.73 s and it was inversely correlated with the velocity of anaerobic threshold (r = -0.54, p < 0.05). This fact, associated with the inverse relationship between TLim and vVO(2)max (r = -0.47, but only for p < 0.10), suggested that swimmers' lower level aerobic metabolic rate might be associated with a larger capacity to sustain that exercise intensity. O(2)SC reached 274.11 +/- 152.83 l/min and was correlated with TLim (r = 0.54), increased ventilation in TLim test (r = 0.52) and energy cost of the respiratory muscles (r = 0.51), for p < 0.05. These data suggest that O(2)SC was also observed in the swimming pool, in high level swimmers performing at vVO(2)max, and that higher TLim seems to correspond to higher expected O(2)SC amplitude. These findings seem to bring new data with application in middle distance swimming.     

Relationship of ergometer-specific VO2 max and muscle enzymes to blood lactate during submaximal exercise.

This study compared the relationship of maximum oxygen uptake and skeletal muscle enzyme activities to the submaximal exercise intensity eliciting 4 mM blood lactate (OBLA). Twelve subjects performed both cycle (Cy) and treadmill (Tr) submaximal exercise with step-wise increments each fourth minute. Blood lactate concentration and oxygen uptake (VO2) were determined during the final minute of each step. Peak VO2 during exhaustive exercise was also measured on each ergometer. Biopsies were taken from the gastrocnemius (gast) and vastus lateralis (vl) muscles as representatives of muscles recruited during Tr and Cy exercise, respectively. Citrate synthase (CS), phosphofructokinase (PFK), and lactate dehydrogenase (LDH) activities were assayed. Peak VO2 was 10% greater and the VO2 at OBLA was 16% greater during Tr compared to Cy exercise. The percent of peak VO2 at OBLA was 85% and 79% for Tr and Cy exercise, respectively. The absolute enzyme activities were not different in the two muscles, however the ratio LDH/CS was greater in the vl than in the gast. The results indicate that the absolute differences between Cy and Tr exercise in peak VO2 are not commensurate with the differences in the relative exercise intensity at which OBLA occurs.     

The relationship between the VO2 slow component, muscle metabolites and performance during very-heavy exhaustive exercise.

This study examined the relationship between the V O(2) response, particularly the slow component (SC), muscle metabolite changes and performance during very-heavy exhaustive exercise. Sixteen active females performed a graded exercise test to determine V O(2peak) and the lactate threshold followed 48h later by a constant-load cycle test to exhaustion (ET) at 85% V O(2peak) intensity. Muscle biopsies and capillary blood samples were obtained before and after the ET to determine changes in muscle ATP, pH, lactate and phosphocreatine and also plasma pH and lactate. Breath-by-breath data from the ET were smoothed using 5-s averages and fit to a three-component exponential model. The mean time to exhaustion (t(exh)) during the ET was 16.8 (+/-6.4) min. Results showed no correlation between the SC and t(exh) or any muscle metabolite changes (p>0.05). Significant correlations (p<0.05) were evident between t(exh) and tau; tau(0) (r=-0.54), tau(1) (r=-0.65), change in (Delta) pH(b) (r=-0.60), Delta[La(-)](b) (r=-0.58) and [La(-)](b post) (r=-0.64). Significant correlations (p<0.05) were also evident between tau(1) and [La(-)](b post) (r=0.54). Furthermore, a negative value resulted when the accumulated oxygen deficit was calculated for the entire duration of the ET. Results showed no association between the amplitude of the SC and t(ext) or to changes in muscle/blood metabolites, suggesting that the SC is not a determinant of high-intensity exercise tolerance. Furthermore, it is possible that a reduced perturbation of anaerobic energy sources, as a result of a faster tau(1), may have contributed to a longer t(exh).     

Plasma lactate accumulation and distance running performance

Laboratory and field assessments were made on eighteen male distance runners. Performance data were obtained for distances of 3.2, 9.7, 15, 19.3 km (n = 18) and the marathon (n = 13). Muscle fiber composition expressed as percent of slow twitch fibers (%ST), maximal oxygen consumption (Vo2max), running economy (Vo2 for a treadmill velocity of 268 m/min), and the Vo2 and treadmill velocity corresponding to the onset of plasma lactate accumulation (OPLA) were determined for each subject. %ST (R greater than or equal to .47), Vo2max (r greater than or equal to .83), running economy (r greater than or equal to .49), Vo2 in ml/kg min corresponding to the OPLA (r greater than or equal to .91) and the treadmill velocity corresponding to the OPLA (r greater than or equal to .91) were significantly (p less than .05) related to performance at all distances. Multiple regression analysis howed that the treadmill velocity corresponding to the OPLA was most closely related to performance and the addition of other factors did not significantly raise the multiple R values suggesting that these other variables may interact with the purpose of keeping plasma lactates low during distance races. The slowest and fastest marathoners ran their marathons 7 and 3 m/min faster than their treadmill velocities corresponding to their OPLA which indicates that this relationship is independent of the competitive level of the runner. Runners appear to set a race pace which allows the utilization of the largest possible Vo2 which just avoids the exponential rise in plasma lactate.     

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.     

A disproportionate increase in VO2 coincident with lactate threshold during treadmill exercise.

PURPOSE: The purpose of this study was to assess the relationship between pulmonary VO2 and running speed over a range of exercise intensities. During constant-load cycle exercise above the lactate threshold (Tlac), it has been shown that VO2 does not attain a steady state within 3 min but continues to rise until either a delayed but elevated steady-state VO2 is attained or exhaustion occurs. Since this greater oxygen cost of exercise (V02 slow component) has only been demonstrated at discrete exercise intensities above Tlac, it was hypothesised that the onset of the VO2 slow component would coincide with Tlac during an incremental test if the stage durations were of sufficient length. METHODS: Five male subjects (mean +/- SD age 31 +/- 2 yr: VO2peak 60.1 +/- 5.8 mL x kg(-1) x min(-1)) performed four identical treadmill tests within an 8-d period. The tests involved the completion of six stages of 7-min duration. Running speed was increased by 0.5 km x h(-1) between stages. In the first test, fingertip capillary blood was sampled at the end of each stage for determination of Tlac. For all tests expired air was collected into Douglas bags from 3.0 to 3.75 min and from 6.0 to 6.75 min of each stage to determine any increase in V02 (deltaVO2) over the duration of the stage. RESULTS: The mean deltaVO2 for each stage over the four tests was determined for each subject. Repeated measures ANOVA with post-hoc Tukey tests revealed a significant increase in deltaVO2 at running speeds above, but not below, Tlac. CONCLUSIONS: The results of this study confirm the close association between the VO2 slow component and the onset of lactic acidosis and demonstrate alinearity in the VO2-exercise intensity relationship above Tlac for incremental treadmill exercise.     

The VO2 slow component: relationship between plasma ammonia and EMG activity

PURPOSE: An increased recruitment of type II muscle fibers has been suggested as a major cause of the slow component of O(2) uptake (VO(2)) kinetics. Furthermore, the rise in plasma ammonia (NH(3)) during high-intensity exercise, where a slow component is observed, has been associated with the activation of type II muscle fibers. Therefore, the purpose of this study was to examine the relationship between the VO(2) slow component, plasma NH3 concentration, and electromyography (EMG) responses during constant-load cycling. METHODS: Eight healthy adults (mean age +/- SEM: 21.4 +/- 1.0 yr) performed 7 min of heavy constant-load exercise. The breath-by-breath VO(2) response was characterized using a two-term exponential model. Plasma NH(3) concentration was measured at rest, following 3 min of unloaded cycling and at 3 and 7 min of constant-load exercise. Surface EMG activity of the right vastus lateralis muscle was measured during the final 10 s of every minute of exercise. RESULTS: The amplitude of the slow component was 561 +/- 52 mL.min(-1), and occurred 132 +/- 11 s following the onset of constant-load exercise. Plasma NH(3) concentration increased significantly from 3 to 7 min of constant-load exercise by 32.2 +/- 2.9 micromol.L(-1). The rise in plasma NH(3) concentration correlated significantly with the amplitude of the slow component (r = 0.79, P < 0.05). The mean power frequency of the EMG increased significantly while the integrated EMG/VO(2) ratio remained constant over the duration of the slow component. CONCLUSION: The rise in NH(3) concentration and the amplitude and spectral components of the EMG are consistent with a progressive increase in the recruitment of type II muscle fibers during the slow component phase of exercise.     

Relationship among oxygenation, myoelectric activity, and lactic acid accumulation in vastus lateralis muscle during exercise with constant work rate

The purpose of this study was to determine whether oxygenation in localized working muscle depended on the muscle activity and on the lactic acidosis level. Seven healthy male subjects underwent the five 6-min cycling exercises with work rates of 50 watts (25.0 +/- 5.0% VO2max), 100 watts (36.6 +/- 6.2% VO2max), 150 watts (50.6 +/- 7.7% VO2max), 200 watts (67.8 + 6.9% VO2max), and 250 watts (82.9 +/- 7.5% VO2max) while gas exchange parameters and blood lactate concentration (BL) were measured. We also measured oxygenated hemoglobin and myoglobin concentration (oxy-Hb/Mb) with continuous-wave near infrared spectroscopy (NIR) and surface myoelectric activity with surface electrodes (EMG). The NIR probe and electrodes were positioned on the vastus lateralis muscle of the right leg. The relative change in oxy-Hb/Mb was estimated by regarding oxy-Hb/Mb in the resting condition as 100% and that obtained during thigh occlusion as 0%. The mean values of oxy-Hb/Mb and integrated EMG (iEMG) were determined from 5'30" to 6'00" at each work rate. The percentage of oxy-Hb/Mb was sustained at the first two work rates corresponding to 25.0 +/- 5.0 and 36.6 +/- 6.2% VO2max and decreased slightly at 150 watts corresponding to 50.6 +/- 7.7% VO2max, which was followed by a linear decrease at 200 and 250 watts corresponding to 67.8 +/- 6.9 and 82.9 +/- 7.5% VO2max. The iEMG, however, was increased slowly at 25.0 +/- 5.0 to 50.6 +/- 7.7% VO2max, and a rapid increment of the iEMG occurred at 67.8 +/- 6.9 and 82.9 +/- 7.5% VO2max. BL was sustained at 25.0 +/- 5.0 to 50.6 +/- 7.7% VO2max and increased linearly at 67.8 +/- 6.9 and 82.9 +/- 7.5% VO2max. There was a significant negative correlation for each subject between the percentage of oxy-Hb/Mb and iEMG (r = -0.947 to -0.993), between the percentage of oxy-Hb/Mb and BL (r = -0.890 to -0.982), and between the percentage of oxy-Hb/Mb and VO2 (r = -0.929 to -0.994) These results indicated that oxygenated hemoglobin/myoglobin concentration measured with NIR reflected the muscle activity and the lactic acidosis.     

.VO2 kinetics during supramaximal exercise: relationship with oxygen deficit and 800-m running performance

The aim of this study was to compare .VO2 kinetics of highly- versus recreationally-trained subjects during a constant velocity test of supramaximal intensity. Eighteen trained male subjects were recruited to one of two groups: highly trained (HT, n = 8, .VO(2max) = 70.1 +/- 6.5 ml . min (-1) . kg (-1)) and recreationally trained (RT, n = 10, .VO(2max) = 63.2 +/- 6.4 ml . min (-1) . kg (-1)). All subjects performed an incremental test to exhaustion for the determination of .VO(2max) and peak treadmill velocity (PTV), two constant velocity tests at 110 % of PTV to determine .VO2 kinetics and oxygen deficit (O(2)def), and a 800-m time trial to determine running performance (mean velocity over the distance, V (800 m)). We found significant differences between HT and RT for the on-transient of the .VO2 response (tau, 24.7 +/- 3.3 and 30.9 +/- 7.0 s, respectively), the amplitude of the .VO2 response (60.0 +/- 5.0 and 53.5 +/- 5.7 ml . min (-1) . kg (-1), respectively) and V (800 m) (6.27 +/- 2.1 and 5.45 +/- 0.38 m . s (-1), respectively). O(2)def (24.6 +/- 2.7 and 27.7 +/- 7.8 ml . kg (-1), respectively) and the gain of the .VO2 response (193 +/- 14 and 194 +/- 13 ml . kg (-1) . m (-1), respectively) were similar between groups. tau was associated with O(2)def (r = 0.90, p < 0.05), but not with V (800 m) (r = 0.30, p > 0.05). It was concluded that HT subjects exhibited faster on-kinetics and higher amplitude than their RT counterparts. The higher amplitude was not thought to reflect any difference in underlying physiological mechanisms. The faster tau, whose exact mechanisms remain to be elucidated, may have practical implications for coaches.     

Muscle activation of vastus medialis obliquus and vastus lateralis during a dynamic leg press exercise with and without isometric hip adduction

ObjectivesTo investigate the effects of submaximal and vigorous isometric hip adduction on the vastus medialis obliquus (VMO) and vastus lateralis (VL) activity during the leg press exercise from 90° of knee flexion until full extension.DesignExperimental.SettingUniversity biomechanics laboratory.ParticipantsTen healthy male college students.Main outcome measuresElectromyographic (EMG) activation of VMO, VL and hip adductor longus (HAL) of the dominant leg were recorded during double leg press (LP), leg press with submaximal isometric hip adduction force (LP+), and leg press with vigorous isometric hip adduction force (LP++). The VMO, VL muscle activation, as well as the VMO/VL ratio between different leg press exercises were analyzed by MANOVA over concentric and eccentric phases, and in 15° increments of knee flexion motion. The effect size was calculated.ResultsNeither LP+ nor LP++ changed the overall VMO-VL activation patterns. Specific to knee angle, however, small to medium effect size was shown with incorporation of isometric hip adduction to the leg press exercise for VMO/VL ratio.ConclusionTargeted training using the leg press exercise to the last 45° of knee extension/flexion with vigorous hip adduction may be useful in promoting a greater VMO/VL ratio.     

Serum and saliva cortisol responses and blood lactate accumulation during incremental exercise testing.

In six male physically active subjects the adrenocortical and metabolic changes in response to incremental exercise testing were investigated. Blood and saliva samples were taken at rest, at the end of every workload (duration 4 min with 50 W increment), immediately and 10 min after 1 min all out spurt on the electrically braked cycle ergometer. Both saliva and serum cortisol were measured as well as blood lactate. The cortisol response in serum and in saliva showed similar dynamics (r = 0.86, p less than 0.001, n = 50) at submaximal work. At maximal work the serum cortisol concentration showed a transitory decrease, which was not manifested in saliva. It is hypothesized that a factor related to the metabolic acidosis masks the actual adrenocortical response in the serum but not in saliva. Correlation analysis revealed a positive relation between lactate and cortisol in serum (r = 0.56, p less than 0.01, n = 50) and saliva (r = 0.70, p less than 0.01, n = 50). Apparently, salivary cortisol closely reflects plasma free cortisol level, presenting advantage over total cortisol measurements. Moreover salivary measurement will permit studies in their authentic settings and should assist attempts to understand the nature of the adrenocortical function in exercise.     

Motor control of the vastus medialis oblique and vastus lateralis muscles is disrupted during eccentric contractions in subjects with patellofemoral pain

BACKGROUND: Inappropriate control of the vastus medialis oblique and vastus lateralis muscles by the central nervous system can contribute to maltracking of the patella. HYPOTHESIS: The activation timing and amplitude of the vastus medialis oblique and vastus lateralis muscles will be different between normal subjects and patients with patellofemoral pain. STUDY DESIGN: Controlled laboratory study. METHODS: Subjects with patellofemoral pain and asymptomatic control subjects performed maximum voluntary knee extension contractions initiated from a flexed and an extended position. The activation timing and amplitude of the vastus lateralis and vastus medialis oblique muscles were quantified from the recorded electromyographic signals. RESULTS: There were no between-group differences in activation timing. The activation amplitude of the vastus medialis oblique and vastus lateralis muscles of the patellofemoral pain subjects was altered to the greatest extent during eccentric contractions and differed significantly from that of control subjects. CONCLUSIONS: The activation amplitudes of the vastus medialis oblique and vastus lateralis muscles of subjects with patellofemoral pain are consistent with a laterally tracking patella during eccentric contractions. Clinical Relevance: The findings suggest the clinical importance of determining whether altered activation patterns are sensitive to rehabilitation, and, if so, if subjective reports of knee joint pain and function parallel changes in the activation patterns as a result of rehabilitation.