Prolonged Running Research Articles

Soreness-related changes in three-dimensional running biomechanics following eccentric knee extensor exercise

Runners often experience delayed onset muscle soreness (DOMS), especially of the knee extensors, following prolonged running. Sagittal knee joint biomechanics are altered in the presence of knee extensor DOMS but it is unclear how muscle soreness affects lower limb biomechanics in other planes of motion. The purpose of this study was to assess the effects of knee extensor DOMS on three-dimensional (3D) lower limb biomechanics during running. Thirty-three healthy men (25.8 ± 6.8 years; 84.1 ± 9.2 kg; 1.77 ± 0.07 m) completed an isolated eccentric knee extensor damaging protocol to elicit DOMS. Biomechanics of over-ground running at a set speed of 3.35 m s−1±5% were measured before eccentric exercise (baseline) and, 24 h and 48 h following exercise in the presence of knee extensor DOMS. Knee flexion ROM was reduced at 48 h (P = 0.01; d = 0.26), and peak knee extensor moment was reduced at 24 h (P = 0.001; d = 0.49) and 48 h (P < 0.001; d = 0.68) compared to baseline. Frontal and transverse plane biomechanics were unaffected by the presence of DOMS (P > 0.05). Peak positive ankle and knee joint powers and, peak negative knee joint power were all reduced from baseline to 24 h and 48 h (P < 0.05). These findings suggest that knee extensor DOMS greatly influences sagittal knee joint angular kinetics and, reduces sagittal power production at the ankle joint. However, knee extensor DOMS does not affect frontal and transverse plane lower limb joint biomechanics during running.

300 plus days on ECMO – lessons learned

Background: Veno-venous extracorporeal membrane oxygenation (VV-ECMO) provides the respiratory support in acute severe respiratory failure until the underlying acute lung pathology improves. 1,2 VV-ECMO support for >100 days is rare and in most situations requires a destination therapy of lung transplant. 3,4 This may not be an option in some centers. We had our longest ECMO case of >300 days with severe residual fibrotic lung disease and inability to wean off ECMO. This presentation briefly discusses the multifaceted challenges and lessons learned from this experience. Discussion/lessons learned: Prolonged ECMO can lead to various challenges, some of which are briefly described below. 1. General ECMO-related issues: These are more common due to prolonged ECMO run and include membrane failure, thrombosis, DIC, etc. Right ventricular failure may prove to be a terminal event in these patients. 2. Rare ECMO-related issues: Prolonged heparin therapy may lead to osteoporosis and heparin-induced thrombocytopeni...

ACTN3 genotype influences exercise-induced muscle damage during a marathon competition

Exercise-induced muscle damage has been identified as one of the main causes of the progressive decrease in running and muscular performance in marathoners. The aim of this investigation was to determine the influence of the ACTN3 genotype on exercise-induced muscle damage produced during a marathon. Seventy-one experienced runners competed in a marathon race. Before and after the race, a sample of venous blood was obtained and maximal voluntary leg muscle power was measured during a countermovement jump. In the blood samples, the ACTN3 genotype (R577X) and the changes in serum creatine kinase and myoglobin concentrations were measured. Data from RX heterozygotes and XX mutant homozygotes were grouped as X allele carriers and compared to RR homozygotes. At the end of the race, X allele carriers presented higher serum myoglobin (774 ± 852 vs 487 ± 367 UL-1; P = 0.02) and creatine kinase concentrations (508 ± 346 vs 359 ± 170ngmL-1; P = 0.04) than RR homozygotes. Pre-to-post-race maximal voluntary leg muscle power reduction was more pronounced in X allele carriers than RR homozygotes (-34.4 ± 16.1 vs -27.3 ± 15.4%; P = 0.05). X allele carriers self-reported higher levels of lower limb muscle pain (7 ± 2 vs 6 ± 2cm; P = 0.02) than RR homozygotes at the end of the race. In comparison to RR homozygotes, X allele carriers for the R577X polymorphism of the ACTN3 gene presented higher values for typical markers of exercise-induced muscle damage during a competitive marathon. Thus, the absence of a functional α-actinin-3 produced by the X allele might induce higher levels of muscle breakdown during prolonged running events.

Effects of chronic nitric oxide synthase inhibition on V’O2max and exercise capacity in mice

Acute inhibition of NOS by L-NAME (Nω-nitro-L-arginine methyl ester) is known to decrease maximal oxygen consumption (V'O2max) and impair maximal exercise capacity, whereas the effects of chronic L-NAME treatment on V'O2max and exercise performance have not been studied so far. In this study, we analysed the effect of L-NAME treatment, (LN2 and LN12, respectively) on V'O2max and exercise capacity (in maximal incremental running and prolonged sub-maximal incremental running tests), systemic NO bioavailability (plasma nitrite (NO2-) and nitrate (NO3-)) and prostacyclin (PGI2) production in C57BL6/J mice. Mice treated with L-NAME for 2weeks (LN2) displayed higher V'O2max and better running capacity than age-matched control mice. In LN2 mice, NO bioavailability was preserved, as evidenced by maintained NO2- plasma concentration. PGI2 production was activated (increased 6-keto-PGF1α plasma concentration) and the number of circulating erythrocytes (RBC) and haemoglobin concentration were increased. In mice treated with L-NAME for 12weeks (LN12), NO bioavailability was decreased (lower NO2- plasma concentration), and 6-keto-PGF1α plasma concentration and RBC number were not elevated compared to age-matched control mice. However, LN12 mice still performed better during the maximal incremental running test despite having lower V'O2max. Interestingly, the LN12 mice showed poorer running capacity during the prolonged sub-maximal incremental running test. To conclude, short-term (2weeks) but not long-term (12weeks) treatment with L-NAME activated robust compensatory mechanisms involving preservation of NO2- plasma concentration, overproduction of PGI2 and increased number of RBCs, which might explain the fully preserved exercise capacity despite the inhibition of NOS.

Prolonged Intermittent Running Induces Inspiratory-Muscle Fatigue in Female Runners

Prolonged Intermittent Running Induces Inspiratory-Muscle Fatigue in Female Runners

APPLICABILITY OF FS-ALL-METAL SELF-LOCK NUTS FOR RAILWAY ROLLING STOCK OF 1520 MM GAUGE

Purpose. One of key requirements for rolling stock of next generation is essential increase of warranty period or running between maintenance depots and in periods between programming repair works. This will lead to a reduction of costs to maintenance and repair during service life of rolling stock. In this regard, the industry aspires to use (during construction, repairs, modernization of rolling stock) a modern screw joints in structures for fixing parts. These screw joints could provide a high reliability under the action of vibration load. FS-hexagon all-metal self-lock nuts of multiple use, Flaig + Hommel GmbH company meets these requirements. Therefore, there is the need to consider the results of tests to confirm the reliability of FS-nuts in the new environment. Methodology. Test complex of developed programs and methods was carried out on railway rolling stock for functional demonstration of screw joints with FS-nuts. These tests include: 1) proof test and locking moment test as specified in ISO 2320 under normal climatic conditions and after low temperatures impact; 2) running test for rolling stock, secured the most load condition and according to supervised operation of next generation cars on the railway. Findings. Results of the tests testify that FS-all-metal self-lock nuts meet the requirements of international standards and confirm the reliability of the next generation rolling stock during its operation on the railway of 1520 mm gauge. Namely, locking moment and tightening torque is maintained in screw joints both on spring-suspended and unspring parts of freight car bogies by the action of vibration load under multiple use of FS-nuts. Originality. The developed software and methods was improved by conducting additional tests after exposure of screw joints with FS-nuts to low temperatures, as well as by control operations for assessing the condition of screw joints with FS-nuts, in the conditions of controlled operation of rolling stock. It fully allows confirming the reliability of the FS-nuts on the rolling stock of 1520 mm gauge railways.Practical value. Application of FS-nuts makes it possible to stop using secondary members in screw joints of railway rolling stock of 1520 mm gauge. These secondary members are used for reaction to slacking under vibration and consist of castle nuts, retaining washers, locking washers, serrated washers, check plates, disposable clamps. Using FS-nuts allow providing the rating rules for next generation of rolling stock. Besides the modern technologies of FS-nuts production provide their prolonged running time under the conditions of pollution, humidity, differential temperature and other adverse factors.

Effects of Prolonged Running-Induced Fatigue on the Periodicity of Shank-Foot Segment Coupling and Free Torque

Objective: The purpose of this study was to determine the periodicity of shank-foot segment coupling and free torque before and after fatigue induced by prolonged running. Method: Fifteen young healthy male participants with a rear-foot strike ran on instrumented dual-belt treadmills at 70% of their maximum oxygen uptake for 65 min. Kinematic and ground reaction force data were collected for 20 continuous strides at 5 and 65 min (considered the fatigued condition). The approximate entropy tool was applied to assess the periodicity of the shank internal-external rotation, foot inversion-eversion, shank-foot segment coupling, and free torque for the two running conditions. Results: The periodicity of all studied parameters, except foot inversion-eversion, decreased after 65 min of running (fatigued condition) for 80% of the participants in this study. Furthermore, 60% of the participants showed similarities in the change of periodicity pattern in shank internal-external rotation, coupling, and free torque. Conclusion: The findings indicated that the foot inversion-eversion motion may pose a higher risk of injury than the shank internal-external rotation, coupling, and free torque in the fatigued condition during prolonged running.

Individual responses in biomarkers of health after marathon and half-marathon running: is age a factor in troponin changes?

Although strenuous physical activity is known to cause notable perturbations in blood chemistries, only few studies exist observing exercise-induced simultaneous changes in biomarkers of health status. We compared markers of muscle, cardiovascular, renal, hepatic and inflammatory status at baseline and at 3-h and at 48-h postrace in recreational runners who successfully completed either a marathon (mean age 27 ± 13 years, finishing time 199 ± 8 min, n = 4) or half-marathon (mean age 38 ± 13 years, finishing time 131 ± 6 min, n = 6) race. Significant postrace changes occurred in myoglobin (p < .001), creatinine kinase (p < .01), CK-MB-mass (p < .01), high sensitivity troponin I (p < .05), high sensitivity troponin T (p < .05), brain natriuretic peptide (p < .001), creatinine (p < .01), aminotransferase enzymes (p < .001 for AST and p < .01 for ALT), uric acid (p < .001) cortisol (p < .01), C-reactive protein (p < .05), leukocytes (p < .001), haematocrit (p < .05) and mean corpuscular volume (p < .01). In comparison between the two types of exercise, marathon running lead to more pronounced responses in myoglobin, CK-MB-mass, ALT, AST, lactate and phosphate. Notable elevations in troponin levels were observed only in young participants (<30 years), most strikingly in those ≤20 years of age. The data indicates that prolonged running leads to distinct biomarker alterations, which should be considered in the assessment of health status after recent acute bouts of strenuous exercise. The observations suggesting more pronounced cardiac troponin responses in young individuals warrant further studies in larger populations.

A comprehensive evaluation of physical and environmental performances for wet-white leather manufacture

This paper presents the comprehensive evaluation results of physical and environmental performances for a novel wet-white (chrome-free) leather manufacturing. The tanning process is optimized as 15 wt% tannic acid (TA) combination with 4 wt% Laponite nanoclay, giving the leather with shrinkage temperature (Ts) above 86 °C. Inductively coupled plasma-atomic emission spectrometry (ICP-AES) measurements indicate that Laponite can be evenly and tightly bound within the leather matrix, which is further confirmed by scanning electron microscopy and energy dispersive X-ray (SEM-EDX) spectroscopy analysis. The resultant wet-white leathers have reasonable good physical properties that can meet the standard requirements for furniture leather without containing hazardous Cr(VI) and formaldehyde. Further life cycle assessment (LCA) studies shows that tanning process is the main contributor to environmental impact categories in the wet-white tanning process, and tannic acid is the most significant substance factor. Compared to conventional chrome tanning, the wet-white tanning process exhibits much lower abiotic depletion potential (ADP), and reduced global warming potential (GWP) and human toxicity potential (HTP) impacts due to the nature of vegetable tanning; whereas, GWP excluding biogenic carbon and energy consumption are higher owing to prolonged run time.

Fatigue associated with prolonged graded running.

Scientific experiments on running mainly consider level running. However, the magnitude and etiology of fatigue depend on the exercise under consideration, particularly the predominant type of contraction, which differs between level, uphill, and downhill running. The purpose of this review is to comprehensively summarize the neurophysiological and biomechanical changes due to fatigue in graded running. When comparing prolonged hilly running (i.e., a combination of uphill and downhill running) to level running, it is found that (1) the general shape of the neuromuscular fatigue-exercise duration curve as well as the etiology of fatigue in knee extensor and plantar flexor muscles are similar and (2) the biomechanical consequences are also relatively comparable, suggesting that duration rather than elevation changes affects neuromuscular function and running patterns. However, 'pure' uphill or downhill running has several fatigue-related intrinsic features compared with the level running. Downhill running induces severe lower limb tissue damage, indirectly evidenced by massive increases in plasma creatine kinase/myoglobin concentration or inflammatory markers. In addition, low-frequency fatigue (i.e., excitation-contraction coupling failure) is systematically observed after downhill running, although it has also been found in high-intensity uphill running for different reasons. Indeed, low-frequency fatigue in downhill running is attributed to mechanical stress at the interface sarcoplasmic reticulum/T-tubule, while the inorganic phosphate accumulation probably plays a central role in intense uphill running. Other fatigue-related specificities of graded running such as strategies to minimize the deleterious effects of downhill running on muscle function, the difference of energy cost versus heat storage or muscle activity changes in downhill, level, and uphill running are also discussed.

Can Trained Runners Effectively Attenuate Impact Acceleration During Repeated High-Intensity Running Bouts?

The purpose of this study was to investigate the effects of prolonged high-intensity running on impact accelerations in trained runners. Thirteen male distance runners completed two 20-minute treadmill runs at speeds corresponding to 95% of onset of blood lactate accumulation. Leg and head accelerations were collected for 20 s every fourth minute. Rating of perceived exertion (RPE) scores were recorded during the third and last minute of each run. RPE responses increased (P < .001) from the start (11.8 ± 0.9, moderate intensity) of the first run to the end (17.7 ± 1.5, very hard) of the second run. Runners maintained their leg impact acceleration, impact attenuation, stride length, and stride frequency characteristics with prolonged run duration. However, a small (0.11-0.14g) but significant increase (P < .001) in head impact accelerations were observed at the end of both first and second runs. It was concluded that trained runners are able to control leg impact accelerations during sustained high-intensity running. Alongside the substantial increases in perceived exertion levels, running mechanics and frequency domain impact attenuation levels remained constant. This suggests that the present trained runners are able to cope from a mechanical perspective despite an increased physiological demand.

The effects of a systematic increase in relative humidity on thermoregulatory and circulatory responses during prolonged running exercise in the heat

ABSTRACTThis study examined the thermoregulatory and circulatory responses, and exercise performance of trained distance runners during exercise in the heat (31°C) at varying relative humidity (RH). In a randomized order, 11 trained male distance runners performed 5 60 min steady-state runs at a speed eliciting 70% of VO2max in RH of 23, 43, 52, 61 and 71%. This was followed immediately with an incremental exercise test to volitional exhaustion. Core (Tre) and mean skin temperature (T¯sk), cardiac output (Q), heart rate (HR), and stroke volume (SV) were recorded at regular intervals. A significant (P = 0.003) main effect was detected for RH on mean body temperature (Tb), with a significantly higher Tb detected during steady-state exercise in the 61 and 71% RH compared to that in the 23% RH. During the steady-state exercise, no differences were detected in whole body sweat loss (P = 0.183). However, a significant main effect of RH was observed for HR and SV (P = 0.001 and 0.006, respectively) but not Q (P = 0.156). The time to exhaustion of the incremental exercise test was significantly reduced at 61 and 71% RH compared with 23% RH (P = 0.045 and 0.005, respectively). Despite an increase in dry heat loss, a greater thermoregulatory and circulatory stress was evident during steady-state exercise at 61 and 71% RH. This ultimately limits the capacity to perform the subsequent incremental exercise to exhaustion. This study highlighted that in a warm environment, the range of the prescriptive zone progressively narrows as RH increases.

Compression Garment with Moderate Pressure Attenuated Decrement of Muscular Performance and Inflammation During Prolonged Running

PURPOSE:To investigate the effect of wearing lower body compression garment (CG) with exerting different pressure levels during prolonged running on exercise-induced muscle damage and inflammatory responses. METHODS: Nine male subjects (23.2 ± 0.4 years, 170.5 ± 0.4 cm, 62.6 ± 0.7 kg) completed 3 exercise trials in a random order. The exercise consisted of 120 min of uphill running (7%) on treadmill at 60 % of VO2max. The exercise trials included 1) wearing lower body CG with exertion of 40 hPa of compression [HIGH]; 2) wearing lower body CG with exertion of 20 hPa of compression [MED]; and 3) wearing lower body CG with exertion of under 10 hPa of compression [LOW]. Time-courses of changes in jump height, heart rate (HR) and rating of perceived exertion (RPE) for respiration and legs were monitored. Blood samples were also drawn to determine blood glucose, lactate, serum creatine kinase, myoglobin, free fatty acid, glycerol, cortisol and plasma IL-6 concentrations. P < 0.05 was considered to be statistically significant. RESULTS: Jump performance was decreased immediately after exercise compared with pre-values in the HIGH and LOW trials, whereas jump performance did not change significantly in the MED trial. Furthermore, the MED trial showed significantly higher value of jump height compared with the HIGH trial immediately after exercise. The HR during exercise was significantly elevated in all trials. However, average HR during 120 min of exercise was significantly lower in the MED trial (159 ± 3 bpm) than in the HIGH (163 ± 3 bpm) and LOW trials (169 ± 5 bpm). Although the RPE for respiratory significantly increased during exercise, the MED trial showed significantly lowest value among 3 trials during latter 60 min of exercise. Plasma IL-6 concentration significantly increased with exercise in all trials. However, area under the curve for IL-6 concentration during 120 min of exercise was significantly lower in the MED trial (397 ± 58 pg/ml•120 min) than in the LOW trial (670 ± 86 pg/ml•120 min). No significant difference among 3 trials was observed for time-course changes in other blood variables. CONCLUSIONS: Wearing lower body CG with exerting moderate pressure (20 hPa) significantly attenuated reduction of power output for lower body muscles and inflammatory response during prolonged running.

The Influence Of Drinking Vs. Rinsing With Water During Prolonged Running Exercise On Affective Response

The Influence Of Drinking Vs. Rinsing With Water During Prolonged Running Exercise On Affective Response

Effects of glucose–fructose versus glucose ingestion on stride characteristics during prolonged treadmill running

Scarce research has examined the effects of carbohydrate composition on running stride characteristics. On two occasions, 14 males and 6 females completed a 120-min sub-maximal run followed by a 4-mile time trial. Participants consumed glucose (GLU) or glucose–fructose (GLU–FRU) beverages supplying 1.3 g/min carbohydrate. Substrate use, psychological affect [Feeling Scale (FS)], and stride characteristics (stride frequency, stride length, and contact time) were assessed. Effects were expressed as Cohen’s d (90% confidence limits [90% CL]). CLs for stride frequency differences at 53 min (90% CL = 0.04–0.21) and 113 min (90% CL = 0.02–0.24) did not cover 0, indicating a positive effect of GLU–FRU. However, effect sizes were small (d = 0.13) and likely-to-very-likely trivial. Energy expenditure differences at sub-maximal end were very likely trivial (d = 0.08; 90% CL = 0.00–0.17), while FS ratings were possibly higher for GLU–FRU at 50 (d = 0.19; 90% CL = −0.10–0.48) and 110 min (d = 0.16; 90% CL = −0.13–0.45). During the time trial, stride length was possibly higher with GLU–FRU (d = 0.13; 90% CL = −0.08–0.33). Glucose–fructose co-ingestion has no significant effect on stride characteristics during constant-velocity running but may result in slightly higher stride length during self-paced running.

Timing of carbohydrate ingestion did not affect inflammatory response and exercise performance during prolonged intermittent running.

BackgroundCarbohydrate ingestion during exercise is known to attenuate exercise-induced elevation of plasma IL-6 concentration. However, the influence of timing of carbohydrate ingestion remains unclear.PurposeThe present study investigated the influence of different timing of carbohydrate ingestion during a simulated soccer game on exercise performance, metabolic and inflammatory responses.MethodsSeven active males performed 3 exercise trials in a randomized order. The exercise consisted of two consecutive bouts of 45 min running (4–16 km/h), separated with 15 min rest period between bouts. The subjects ingested carbohydrate gel (1.0 g/kg) immediately before the first bout of exercise (ONE), immediately before first and second bouts of exercise (0.5 g/kg for each ingestion) (TWO) or placebo immediately before exercise (PLA) Time course changes of maximal jump height, peak power output during 6-s maximal pedaling, perceived fatigue and heart rate (HR) were monitored. Blood samples were also drawn to determine blood glucose, serum insulin, free fatty acid (FFA), myoglobin (Mb), creatine kinase (CK) and plasma IL-6 concentrations.ResultsBlood glucose and serum insulin concentrations were significantly higher in the ONE trial after first bout of 45 min exercise compared with PLA trial (P < 0.05), while serum FFA concentration was significantly elevated in PLA compared with ONE and TWO trials after second bout of exercise (P < 0.05). However, changes of jump height, peak power output during 6-s maximal pedaling, perceived fatigue, HR, or indirect muscle damage (Mb, CK) and inflammatory (IL-6) markers were not significantly different among three trials (P > 0.05).ConclusionsThe timing of carbohydrate ingestion did not affect exercise performance, exercise-induced muscle damage or inflammatory response during a simulated soccer game.

Match demands of professional rugby football codes: A review from 2008 to 2015

Rugby football codes have continually increased in popularity and are played professionally around the world at domestic, national and international level. Coaching professionals can use the findings of this review to guide training practices for the professional rugby football player, particularly those players who may be competing concurrently or transferring between codes. The development of repeated high-intensity exercise ability should be a key emphasis of training programmes especially for players who are aiming to compete at higher competition standards. Importantly, there are considerable differences in repeated high-intensity exercise demands of match-play for different positional groups. For greatest transference to match performance, training programs should replicate the frequency and duration of repeated high-intensity exercise bouts in addition to the relative contribution of high-intensity running, tackling and physical collisions. Training programmes should not neglect developing players’ prolonged high-intensity running ability as high-speed running efforts may occur separately from repeated high-intensity exercise bouts and likely place considerable demands on rugby football players, particularly in rugby sevens competition. Rugby football players have been shown to experience transient fatigue patterns during match-play where teams may be susceptible to conceding points or sustaining injury. Improved physical conditioning strategies may reduce development of match-fatigue; however, research is yet to investigate the influence of fitness levels and team strategies. A better understanding of these factors and how they interact with match-fatigue will assist with the improvement of training practices for professional rugby football players.

Effects of Prolonged Exercise in the Heat and Cool Environments on Salivary Immunoglobulin A among Recreational Athletes

This study aims to determine the effects of prolonged exercise in the heat (31°C) and cool (18°C) environments on salivary Immunoglobulin A (SIgA) among recreational athletes. Thirteen healthy male participants (age: 20.9 ± 1.3 years old) were recruited and randomised in this cross-over study. In this study, participants performed the exercise trials in the heat environment at 31°C first followed by another exercise trial in the cool environment trial at 18°C or vice versa with one week of recovery period. Physiological parameters (heart rate, body weight changes and oxygen uptake) as well as room temperature and relative humidity were recorded. Cool water (3 ml.kg -1 body weight) was given to the participants at every 20 min during both exercise trials. Saliva samples were collected to calculate the saliva flow rate and analysed for salivary Immunoglobulin A (SIgA) concentrations and secretion rate. Paired t-test and two-way ANOVA with repeated measures were performed to analyse the data. The results revealed that saliva flow rate, SIgA concentration, and SIgA secretion rate did not significantly different between exercise trial in the heat and in the cool environments. However, prolonged exercise significantly decreased (p < 0.05) saliva flow rate in both trials with the values return to baseline 1 h post exercise. Salivary IgA concentration and secretion rate were not affected by prolonged running. As a conclusion, SIgA responses did not affected by ambient/room temperature. In addition, prolonged exercise with adequate fluid intake during exercise did not supress SIgA responses thus may not increase infection risk among athletes.

Effect of Prolonged Running-induced Fatigue on Free-torque Components

Running is a popular sport because it demands physical activity and can be performed at a convenient time in any place (Ida et al., 2010). Although running has a positive effect on health, it can have a negative impact on the body because of possible injury. In particular, the incidence of injury from prolonged running is reported to be 30~ 79% (Lun et al., 2004; Taunton et al., 2003; van Gent et al., 2007). There are various possible factors involved in injury from prolonged running, including mechanical abnor- malities previous injuries sex, body mass index, training frequency, intensity, and duration, muscle strength, flexibility, shoes, and fatigue (Taunton et al., 2003). Among prolonged running injuries, stress fractures are a common problem and account for a large proportion of running injuries (Taunton et al., 2002). In prolonged running, stress fractures of the tibia are most common, accounting for 35~56% of the stress fractures caused by prolonged running (Romani et al., 2002). One of the bio- mechanical factors causing tibial stress fractures is free torque (FT) (Milner & Davis, 2006). FT refers to the torque in the vertical axis that is generated by friction between the foot and the ground during the support phase in

Do footfall patterns in forefoot runners change over an exhaustive run?

ABSTRACTThe purpose of this study was to investigate possible footfall pattern changes in habitual forefoot runners over a prolonged, exhaustive run. A prolonged run was performed to exhaustion in 14 habitual forefoot runners. Vertical ground reaction forces (VGRFs) and kinematics were collected at the beginning and end of the run. Ankle plantar flexor torque and triceps surae electromyographic activity were measured during pre- and post-run isometric contractions. By run’s end, there was an increase in VGRF loading rate and impact peak magnitude, greater dorsiflexion at foot contact and greater knee flexion angle throughout stance. Ankle plantar flexor torque decreased significantly from pre- to post-run tests. This was accompanied by a decrease in the integrated electromyographic activity (iEMG) output for the lateral and medial gastrocnemius. There were significant changes in landing mechanics for forefoot runners that indicate a transition towards more midfoot footfall patterns. A contributing factor may be ankle plantar flexor muscle fatigue that, at touchdown, is exposed to exaggerated eccentric loading. These findings suggest that a forefoot running pattern may become difficult to maintain in longer endurance events, and thus runners should pay attention to this in training to improve performance and mitigate potential injury.