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PubMed2006

Medial gastrocnemius muscle behavior during human running and walking.

Utilization of elastic energy in the tendinous tissues (TT) of the human skeletal muscle may be task dependent. The present study was designed to investigate this problem by comparing the fascicle-TT interaction of the medial gastrocnemius muscle (MG) during ground contact of running and walking. Seven subjects ran and walked with a natural cadence. Ankle and knee joint angular data were recorded by electrogoniometers for estimating the entire MG muscle-tendon unit (MTU) length, together with the ground reaction forces. The MG fascicle length was measured by using the high-speed ultrasound image scanning during movements. The results showed that in running, after the rapid early fascicle stretching (0-10% of the contact period), the fascicles shortened throughout the ground contact while TT was stretched prior to shortening. In walking, the fascicles shortened initially (0-15% of the contact period) due to sudden plantar-flexion. Thereafter, the fascicles and TT lengthened slowly until the end of single support (15-70% of the contact period.). The fascicles then shorted during the push-off phase (70-100% of the contact period). These results demonstrate that the MG fascicles behaved differently between running and walking and did not follow the length change pattern of the MTU during the ground contact period. The estimated working range of active muscle fibers in force-length relationship could shift more to an ascending limb (shorter length) phase in running than in walking. These results suggest that MG fascicles can work within the optimal working range of the sarcomeres in the force-length relation but are responsible for the effective utilization of the TT elasticity during human running.

Adult↗

PubMed2006

Lower extremity mechanics of iliotibial band syndrome during an exhaustive run.

Injury patterns in distance running may be related to kinematic adjustments induced by fatigue. The goal was to measure changes in lower extremity mechanics during an exhaustive run in individuals with and without a history of iliotibial band syndrome (ITBS). Sixteen recreational runners ran to voluntary exhaustion on a treadmill at a self-selected pace. Eight runners had a history of ITBS. Twenty-three reflective marker positions were recorded by an eight-camera 120 Hz motion capture system. Joint angles during stance phase were exported to a musculoskeletal model (SIMM) with the iliotibial band (ITB) modeled as a passive structure to estimate strain in the ITB. For ITBS runners, at the end of the run: (1) knee flexion at heel-strike was higher than control (20.6 degrees versus 15.3 degrees, p=0.01); (2) the number of knees with predicted ITB impingment upon the lateral femoral epicondyle increased from 6 to 11. Strain in the ITB was higher in the ITBS runners throughout all of stance. Maximum foot adduction in the ITBS runners was higher versus control at the start of the run (p=0.003). Maximum foot inversion (p=0.03) and maximum knee internal rotation velocity (p=0.02) were higher versus control at the end of the run. In conclusion, ITB mechanics appear to be related to changes in knee flexion at heel-strike and internal rotation of the leg. These observations may suggest kinematic discriminators for clinical assessment.

Adult↗

PubMed2005

Influence of swing leg movement on running stability.

The aim of this study was to investigate the role of the swing leg movement on running stability. A simple model was used describing a forward hopping motion. The model consisted of two sub-models, namely a spring-mass system for the stance phase and a functional control model for the swing phase (represented by a passive or actively driven pendulum). To verify the main simulation results, an experimental study on treadmill running was performed. The results of the model indicated that for certain running speeds and pendulum lengths, the behavior of the mechanical system was stable. The following characteristic dependencies between the model parameters were observed. (1) Pendulum length and hip muscle activity determined running height and therefore swing duration. (2) Horizontal velocity was inversely related to leg angle of attack. Increased speed corresponded to flatter leg angles at touch-down, which is in agreement with experimental studies and previous predictions of spring-mass running. It was shown that a biologically motivated control approach with oscillating leg movements is well capable of generating stable hopping movements. Due to its simplicity, however, the monopedal model failed to explain more detailed mechanisms like the swing-leg to stance-leg interaction or the functional role of the leg segmentation. This simple model is therefore considered as a functional mechanical template for legged locomotion, which could help to build more elaborate models in the future.

Biomechanical Phenomena↗

PubMed2004

Heel-shoe interactions and the durability of EVA foam running-shoe midsoles.

A finite element analysis (FEA) was made of the stress distribution in the heelpad and a running shoe midsole, using heelpad properties deduced from published force-deflection data, and measured foam properties. The heelpad has a lower initial shear modulus than the foam (100 vs. 1050 kPa), but a higher bulk modulus. The heelpad is more non-linear, with a higher Ogden strain energy function exponent than the foam (30 vs. 4). Measurements of plantar pressure distribution in running shoes confirmed the FEA. The peak plantar pressure increased on average by 100% after 500 km run. Scanning electron microscopy shows that structural damage (wrinkling of faces and some holes) occurred in the foam after 750 km run. Fatigue of the foam reduces heelstrike cushioning, and is a possible cause of running injuries.

Adult↗

PubMed2005

Examination of extrinsic foot muscles during running using mfMRI and EMG.

Over-pronation has been cited as a key contributor to many types of running injuries. However, the roles of the extrinsic foot muscles during running have not been adequately identified. The purpose of this study was to examine the muscle functional (mf) MRI and EMG responses to perturbations of the foot by running in varus, neutral and valgus wedged shoes. Ten males ran at 3.6 m/s in specially constructed shoes for 5 min with T2-weighted mfMRI collected before and after each run. The change in T2 from before to after each run characterized the level of metabolic activity in each of muscle. Kinematic and EMG data were also collected while subjects ran on a treadmill. There were no T2 differences across the three shoe conditions. In contrast, there was significantly less EMG activity in the tibialis anterior and soleus while wearing the neutral shoe. Overall, the results did not support the theory that muscle activity would increase as the degree of eversion increased. It also appears that surface EMG was more sensitive to differences between conditions than mfMRI. However, this study illustrated that mfMRI may be a useful tool for quantifying muscle activity in cases where surface EMG is inadequate.

Adaptation, Physiological↗

PubMed2006

Multidimensional analysis of metabolism contributions involved in running track tests.

It is difficult to interpret the training induced changes in middle-distance running, since numerous aerobic and anaerobic determinants of the performance are interdependent. Several aerobic and anaerobic tests are available but their results, particularly those from anaerobic tests, may be discordant, not providing univocal interpretation of training. The purpose of this study is to use a multidimensional approach to distinguish aerobic and anaerobic capacities assessed by two running tests on a track: the maximal anaerobic running test (MART) and V(O2max) tests. Eleven runners carried out two maximal tests on a synthetic track before and after a 4-week training period: (i) a maximal test to determine V(O2max), the velocity associated with V(O2max) (vV(O2max)) and the velocity at the lactate threshold (v(LT)), (ii) a maximal anaerobic running test to estimate anaerobic capacity. An all-out test run at v(LT)+50% of the difference between v(LT) and vV(O2max), known to be affected by both aerobic and anaerobic energy production, was used to test this approach. A principal components analysis (PCA) shows that two components (i.e., aerobic and anaerobic) explained 79% of the variation in the physiological variables. The PCA suggests that V(O2max) and MART tests assess the aerobic and the anaerobic capacities, respectively. In contrast, the performance in the all-out test is affected by both aerobic and anaerobic energy production. The PCA shows that v(LT) and DeltaP (difference between the maximal power of the MART and V(O2max)) are clear markers of the long-term endurance and the anaerobic capacity, respectively. This multidimensional approach can be a useful way to disentangle the aerobic and anaerobic components of track tests.

Adult↗

PubMed2005

Differential responsiveness of c-Fos expression in the rat medulla oblongata to different treadmill running speeds.

Expression of the inducible transcription factor c-Fos was mapped in the rat medulla oblongata to identify the brain areas respond to different running speeds. Rats were subjected to 30 min of running, either at high speed, low speed or just sitting on a treadmill (control). Blood lactate levels were measured to confirm the physiological impact of different exercise intensities. The number of c-Fos-ir cells was counted and their spatial distributions were mapped through the rostral to the caudal level in the medulla. A statistically significant exercise intensity-dependent induction of c-Fos was observed in the nucleus of the solitary tract (NTS) and caudal ventrolateral medulla (CVL) in the medulla. Further, c-Fos induction was more predominant in the caudal part of each nucleus. The present data clearly show that different running speeds cause differential activation of each nucleus in the medulla, and in particular, the caudal parts of the NTS and the CVL are the most responsive to speed changes. The present study identifies brain areas newly found to be responsive to changes in running speed. These findings are likely to be particularly helpful in studies of specific neural circuits and their functions in response to different running speeds.

Animals↗

PubMed2005

Biomechanics and analysis of running gait.

Physical activity, including running, is important to general health by way of prevention of chronic illnesses and their precursors. To keep runners healthy, it is paramount that one has sound knowledge of the biomechanics of running and assessment of running gait. More so, improving performance in competitive runners is based in sound training and rehabilitation practices that are rooted firmly in biomechanical principles. This article summarized the biomechanics of running and the means with which one can evaluate running gait. The gait assessment techniques for collecting and analyzing kinetic and kinematic data can provide insights into injury prevention and treatment and performance enhancement.

Biomechanical Phenomena↗

PubMed2006

Oxytocin levels in the posterior pituitary and in the heart are modified by voluntary wheel running.

We hypothesized that voluntary wheel running results in increased secretion of oxytocin, a peptide involved in the stress response. An additional hypothesis was that prolonged exercise affects oxytocin levels in the heart, which is in line with the potential role of oxytocin in cardiovascular functions. Voluntary wheel running lasted 3 weeks and daily running distances increased progressively reaching maximum levels about 8 km (Sprague-Dawley rats) and 4 km (Lewis strain). The exercise resulted in significant reduction of epididymal fat, slight increase in glucose transporter GLUT4 mRNA levels and significant enhancement of plasma density. Voluntary exercise failed to influence plasma oxytocin levels either in Lewis or Sprague-Dawley rats, but it resulted in a significant decrease of oxytocin concentrations in the posterior pituitary. Plasma oxytocin concentrations were not modified even if the measurements were made in the dark phase of the day. In voluntary wheel running Sprague-Dawley rats, the content of oxytocin in the right heart atrium was lower than in controls. Thus, the present findings demonstrate that prolonged voluntary wheel running results in a decrease in pituitary oxytocin content without evident changes in hormone concentrations in peripheral blood. However, prolonged exercise used has a significant impact on oxytocin levels in the heart.

Animals↗

PubMed2000

Tibiocalcaneal kinematics of barefoot versus shod running.

Barefoot running kinematics has been described to vary considerably from shod running. However, previous investigations were typically based on externally mounted shoe and/or skin markers, which have been shown to overestimate skeletal movements. Thus, the purpose of this study was to compare calcaneal and tibial movements of barefoot versus shod running using skeletal markers. Intracortical bone pins with reflective marker triads were inserted under standard local anesthetic into the calcaneus and tibia of five healthy male subjects. The subjects ran barefoot, with a normal shoe, with three shoe soles and two orthotic modifications. The three-dimensional tibiocalcaneal rotations were determined using a joint coordinate system approach. Test variables were defined for eversion and tibial rotation. The results showed that the differences in bone movements between barefoot and shod running were small and unsystematic (mean effects being less than 2 degrees ) compared with the differences between the subjects (up to 10 degrees ). However, differences may occur during midstance when extreme shoe modifications (i.e. posterior orthosis) are used. It is concluded that calcaneal and tibial movement patterns do not differ substantially between barefoot and shod running, and that the effects of these interventions are subject specific. The result of this in vivo study contrasts with previous investigations using skin and shoe mounted markers and suggests that these discrepancies may be the result of the overestimation with externally mounted markers.

Adult↗

PubMed2003

Does training have consequences for the walk-run transition speed?

A number of authors when studying the walk-run transition phenomenon focused either on the mechanical or energy expenditure whilst only a few used both parameters concurrently. Moreover the literature demonstrates that the contribution of these variables changes along with the level and method of training. Consequently the purpose of this study is to find, by analyzing concurrently these two variables, if the walk-run transition speed is linked to the type of training. To this end we calculated two theoretical transition speeds: one based on the metabolic energy expenditure St(1) and the second one based on the internal work St(2). Subjects were divided into three groups (untrained, sprint and endurance-trained men) who were required to walk and run on a treadmill at increasing speeds. Firstly we show that the relationship between St(1) and St(2) differs depending on the groups. Sprinters have a significantly lower St(2) than St(1) whereas the opposite is found for untrained subjects. We also show that the transition speed is linked to the subject's type of training. To conclude it seems that acquiring running techniques through specific training has consequences for the walk-run transition phenomenon.

Acceleration↗

PubMed2003

Foot orthotics affect lower extremity kinematics and kinetics during running.

OBJECTIVE: To quantify the effects of posting and custom-molding of foot orthotics on lower extremity kinematics and kinetics during running. DESIGN: Repeated measures.Background. Several kinematic and kinetic factors have been suggested to increase a runner's risk for injuries. It has been speculated that foot orthotics can be used to reduce injury related complaints or even prevent running injuries by affecting these factors. METHODS: Twenty one volunteers participated in this study. Kinematic and kinetic variables obtained during overground running for medial posting, custom-molding, and the combination of medial posting and custom-molding of foot orthotics were compared to a control condition. Repeated measures ANOVA and student t-tests were used to detect significant differences (alpha=0.05). RESULTS: Posting of foot orthotics reduced maximum foot eversion and ankle inversion moment and increased vertical loading rate and maximum knee external rotation moment (P<0.05). Molding and posting and molding reduced vertical loading rate and ankle inversion moment and increased maximum foot inversion and maximum knee external rotation moment (P<0.05). CONCLUSIONS: The effects of posting and molding of foot orthotics are extremely different and when combining posting and molding, the effects of molding appear to be dominant. It yet remains to be determined whether posting or molding is more beneficial with respect to overuse running injuries. RELEVANCE: The potential of foot orthotics for reducing pain and injuries is convincing. The current study provides valuable information about the role of specific structural components of foot orthotics and contributes to the knowledge about the mechanism underlying the effect of foot orthotics in running.

Adult↗

PubMed2003

Combined forced running stress and subclinical paraoxon exposure have little effect on pyridostigmine-induced acute toxicity in rats.

Pyridostigmine is a short-acting inhibitor of cholinesterase (ChE) used as a pretreatment against potential nerve agent exposure during the Persian Gulf War. As pyridostigmine contains a quaternary ammonium group, it is generally believed to elicit changes in the peripheral nervous system function only. It has been hypothesized, however, that the neurotoxicity of pyridostigmine may be altered by either stress or combined exposures to other toxicants. We evaluated the effects of forced running stress, exposure to the organophosphate anticholinesterase paraoxon, or a combination of both on the acute neurotoxicity of pyridostigmine. ChE (blood, diaphragm, and selected brain regions) and carboxylesterase (CE; liver, plasma) inhibition was also evaluated. Young adult male Sprague-Dawley rats were either given vehicle or paraoxon (0.1 mg/kg, i.m.) and subsets placed in their home cage or forced to run on a treadmill for 60 min. Pyridostigmine (0, 10 or 30 mg/kg, p.o.) was given 60 min after paraoxon dosing and rats were evaluated for cholinergic toxicity just prior to sacrifice 60 min later. No signs of toxicity were noted following paraoxon exposure while both dosages of pyridostigmine (10 and 30 mg/kg, p.o.) elicited signs of functional toxicity. Toxicity was not different with combined paraoxon-pyridostigmine exposures and forced running did not influence toxicity under any conditions. Paraoxon (0.1 mg/kg, i.m.) caused moderate (23-46%) ChE inhibition in blood, diaphragm and brain 2 h after exposure. Pyridostigmine (10 or 30 mg/kg, p.o.) caused extensive inhibition of blood (88-94%) and diaphragm (75-85%) ChE activity but no significant effect on brain regional ChE activity. Forced running stress did not influence the degree of tissue ChE inhibition following either paraoxon, pyridostigmine or paraoxon-pyridostigmine combined exposures. CE activities were inhibited (26-43%) in plasma and liver by paraoxon but inhibition was not influenced by either stress or combined paraoxon-pyridostigmine exposures. These results suggest that subclinical paraoxon exposure and forced running stress, by themselves or in combination, have little effect on acute pyridostigmine toxicity in rats.

Animals↗

PubMed1999

Changes to the gait initiation programme following a running exercise in human subjects.

The question addressed by the present study was whether the programme for gait initiation is fully invariant or can be modified by a prior long duration running exercise. Eight subjects performed a series of gait initiation movements on a force platform in three different speed conditions before and after running on a treadmill (3.3 m/s, 0% slope). Following the running exercise, the first step length and velocity were greater and the double stance phase duration was shorter, while the relationships between the temporal parameters of gait initiation and the velocity of the centre of gravity at the end of the first step were not significantly different. During the anticipation phase, the maximal variation of the ankle joints moment remained significantly correlated with the integrated EMG activity of the Tibialis Anterior after the run. However the displacement of the centre of foot pressure, displayed some post-exercise changes, indicating a modification to the postural part of the gait initiation programme. The greater velocities reached after the running exercise could be explained by a recalibration of gravitational force control, while the invariance of time necessary to reach these velocities showed the rigidity of the initiation gait.

Adaptation, Physiological↗

PubMed2004

Reproducibility of electromyography and ground reaction force during various running techniques.

This study examined the validity of the assumption of electromyographic (EMG) and vertical ground reaction force (GRF) parameter reproducibility during running at different velocities and stride frequencies. Each of 12 female long distance runners ran on a treadmill in combinations of three velocities (2.5, 3.0 and 3.5 m/s) and three stride frequencies (preferred, +/-10% from preferred). Seven parameters from the GRF and five parameters from the EMG signals from five muscles of the lower extremity were evaluated (1000 Hz). The GRF was analysed by a pressure measuring insoles. A total number of three trials for each running condition were recorded. GRF parameters during all running conditions showed high intraclass correlation coefficients (ICC average 0.87). The ICC of the EMG parameters of gastrocnemius medialis and lateralis were high (r>0.69 in 73% of the data), while those for vastus lateralis (22%), hamstrings (42%) and tibialis anterior (51%) were clearly lower. The results revealed that GRF parameters were reproducible during all running techniques indicating that a single trial would provide reproducible GRF-data. The reproducibility of the EMG parameters was not influenced by the running technique but dependent on the parameter itself and on the muscle studied.

Adult↗

PubMed2002

Bovine colostrum supplementation during endurance running training improves recovery, but not performance.

This study examined the effect of supplementation with concentrated bovine colostrum protein powder (intact) on plasma insulin-like growth factor I (IGF-I) concentrations, endurance running performance and recovery. Thirty physically active males completed 8 weeks of running training whilst consuming 60 g x day(-1) of intact powder (n=17) or a concentrated whey protein powder placebo (n=13) in a randomised, double-blind, parallel design. Plasma IGF-I concentrations were measured prior to subjects performing two (approximately 30 min) incremental treadmill running tests to exhaustion (RUN1 and RUN2) separated by 20 min of passive recovery at Weeks 0. 4 and 8. Plasma IGF-I concentrations showed little change in either group (p=0.83). Effective peak running speed (PRSE; i.e. equivalent of peak power) during RUN1 was not different between groups at Week 0 (p>0.99), and had increased by a similar amount in both groups by Week 4 (mean+/-SD, intact 2.2+/-4.0%, placebo 3.2+/-3.3%; 95% confidence interval [95% CI 15.7 to -13.7%; p=0.89) and Week 8 (intact 3.6+/-5.6%, placebo 3.4+/-4.4 %; 95% CI -100.0 to 100.0%; p>0.99). PRSE was less in both groups during RUN2 (p<0.05), but was not significantly different between groups at Week 0 (p>0.99). PRSE during RUN2 tended to have increased more in the placebo group by Week 4 (intact 1.8+/-4.8%, placebo 4.2+/-3.9%; 95% CI 0.2 to -5 0%; p=0.07), but the intact group had increased PRSE significantly more by Week 8 (intact 4.6+/-6.1%, placebo 2.0+/-4.5%; 95% Cl 0.0 to 5.2%; p=0.05). resulting in a significantly faster PRSE (p=0.003). We conclude that supplementation with intact powder did not increase plasma IGF-I concentrations or improve performance during an initial bout of incremental running to exhaustion in our sample. However, performance during a second bout of exercise may be improved by as much as 5.2% in the average subject after 8 weeks of supplementation, possibly due to an enhancement of recovery.

Adolescent↗

PubMed2005

The oxygen uptake response of sprint- vs. endurance-trained runners to severe intensity running.

We compared the oxygen uptake (VO2) response of sprint- and endurance-trained runners for an exhaustive square wave run lasting approximately 2 minutes. Six sprinters and six middle- and long-distance runners each performed two exhaustive square wave runs lasting approximately 2 min and two exhaustive ramp tests. VO2 was determined breath-by-breath (QP9000; Morgan Medical, Rainham, UK) and averaged across the two repeats of each test; for the square wave test, the averaged VO2 response (excluding the first 15 s) was then modelled using a monoexponential function. Both VO2peak for the ramp test (67.5+/-3.3 vs. 54.5+/-8.5 mlxkg(-1)xmin(-1); P= 0.006) and the asymptotic VO2 for the square wave run (59.6+/-2.7 vs. 50.7+/-4.6 mlxkg(-1)xmin(-1); P= 0.002) were higher for the endurance than for the sprint group. However, as a percentage of VO2peak, this asymptotic VO2 did not differ between the groups (90.1+/-3.2% (endurance) vs. 96.2+/-9.0% (sprint); P= 0.145). Across all 12 subjects, the %VO2peak attained in the square wave run was negatively correlated with VO2peak (Pearson's r= -0.811, P= 0.001). We conclude that VO2max is more important than training history as a determinant of the %VO2max attained in exhaustive square wave running lasting approximately 2 min.

Adult↗

PubMed2001

Chronic stretching and running economy.

Research demonstrates an inverse relationship between the range of motion of selected joint movements (flexibility) and running economy. Since stretching exercises have been shown to increase joint range of motion, stretching exercises may be contraindicated for endurance running performance. Hence, this study investigated the influence of a 10-week program of stretching exercises on the oxygen costs of a 10 min sub-maximal (approx. 70% peak VO(2)) treadmill run. Thirty-two (16 female, 16 male) physically active, treadmill accommodated, college students participated in the study. All participants maintained their current activity level, with half the participants (8 female, 8 male) adding a 40 min, 3 days per week session of thigh and calf muscle stretching exercises. After 10 weeks, the stretching group (STR) exhibited a significant (P<0.05) increase (3.1+/-2.2 cm) in the sit-and-reach, while the non-stretching group (CON) experienced no significant (P>0.05) change (0.0+/-0.4 cm). However, neither the STR nor the CON exhibited a significant (P>0.05) change in the O(2) cost for the submaximal run. It is concluded, therefore, that a chronic stretching program does not necessarily negatively influence running economy.

Adult↗