Joint stiffness and running economy during imposed forefoot strike before and after a long run in rearfoot strike runners

Research has focused on the effects of acute strike pattern modifications on lower extremity joint stiffness and running economy (RE). Strike pattern modifications on running biomechanics have mostly been studied while runners complete short running bouts. This study examined the effects of an imposed forefoot strike (FFS) on RE and ankle and knee joint stiffness before and after a long run in habitual rearfoot strike (RFS) runners. Joint kinetics and RE were collected before and after a long run. Sagittal joint kinetics were computed from kinematic and ground reaction force data that were collected during over-ground running trials in 13 male runners. RE was measured during treadmill running. Knee flexion range of motion, knee extensor moment and ankle joint stiffness were lower while plantarflexor moment and knee joint stiffness were greater during imposed FFS compared with RFS. The long run did not influence the difference in ankle and knee joint stiffness between strike patterns. Runners were more economical during RFS than imposed FFS and RE was not influenced by the long run. These findings suggest that using a FFS pattern towards the end of a long run may not be mechanically or metabolically beneficial for well-trained male RFS runners.     

Altered multi-muscle coordination patterns in habitual forefoot runners during a prolonged,exhaustive run

Abstract

Introduction: In response to fatigue during an exhaustive treadmill run, forefoot runner’s muscles must adapt to maintain their pace. From a neuromuscular control perspective, certain muscles may not be able to sustain the force to meet the run’s demands; thus, there may be alternative muscle coordination in the lower extremity that allows for continued running for an extended period of time. The aim of this study was to quantify the change in muscle coordination during a prolonged run in forefoot runners.

Methods: Thirteen forefoot runners performed exhaustive treadmill runs (mean duration: 15.4?±?2.2?min). The muscle coordination of seven lower extremity muscles was quantified using a high-resolution time–frequency analysis together with a pattern recognition algorithm.

Results: The mean EMG intensity for the lateral and medial gastrocnemius muscles decreased with the run (p?=?0.02; 0.06). The weight factors of the second principal pattern decrease by 128.01% by the end of run (p?=?0.05, Cohen’s d?=?0.42) representing a relatively greater biceps femoris activation in midstance but smaller midstance rectus femoris, vastus medialis, triceps surae, and tibialis anterior activation.

Discussion: These results suggest that forefoot runners cannot sustain plantar flexor activation throughout an exhaustive run and change their muscle coordination strategy as a compensation. Understanding the underlying compensation mechanisms humans use to cope with fatigue will help to inform training modalities to enhance these late stage muscle activation strategies for athletes with the goal of improving performance and reducing injury.     

The effect of shoe type on gait in forefoot strike runners during a 50-km run

PurposeTo observe the relative change in foot-strike pattern, pressure characteristics, surface electromyography (sEMG) recordings, and stride characteristics in forefoot strike runners wearing both minimalist and traditional shoes during a 50-km run.MethodsFour experienced minimalist runners were enrolled in this study. Each runner ran a 50-km simulated run in both minimalist shoes and traditional shoes. Pressure data, sEMG recordings, and limited 3D motion capture data were collected during the initial 0.8 km and final 0.8 km for each trial.ResultsThree runners in the traditional shoe type condition and one runner in the minimalist shoe type condition demonstrated a more posterior initial contact area (midfoot strike (MFS) pattern) after the 50-km run, which was supported by increased activity of the tibialis anterior in the pre-contact phase (as per root mean square (RMS) values). In addition, in both pre- and post-run conditions, there were increased peak pressures in the minimalist shoe type, specifically in the medial forefoot. Muscle fatigue as defined by a decreased median frequency observed in isometric, constant force contractions did not correspond with our hypothesis in relation to the observed foot strike change pattern. Finally, step rate increased and step length decreased after the 50-km run in both shoe type conditions.ConclusionMore runners adopted a more posterior initial contact area after the 50-km run in the traditional shoe type than in the minimalist shoe type. The runners who adopted a more posterior initial contact area were more closely associated with an increased median frequency of the medial gastrocnemius, which suggests there may be a change in motor unit recruitment pattern during long-distance, sustained velocity running. The increased peak pressures observed in the medial forefoot in the minimalist shoe type may predispose to metatarsal stress fractures in the setting of improper training.     

Influence of regression model and incremental test protocol on the relationship between lactate threshold using the maximal-deviation method and performance in female runners

Abstract

This study examined the influence of the regression model and initial intensity of an incremental test on the relationship between the lactate threshold estimated by the maximal-deviation method and the endurance performance. Sixteen non-competitive, recreational female runners performed a discontinuous incremental treadmill test. The initial speed was set at 7 km · h^?1, and increased every 3 min by 1 km · h^?1 with a 30-s rest between the stages used for earlobe capillary blood sample collection. Lactate-speed data were fitted by an exponential-plus-constant and a third-order polynomial equation. The lactate threshold was determined for both regression equations, using all the coordinates, excluding the first and excluding the first and second initial points. Mean speed of a 10-km road race was the performance index (3.04 ± 0.22 m · s^?1). The exponentially-derived lactate threshold had a higher correlation (0.98 ≤ r ≤ 0.99) and smaller standard error of estimate (SEE) (0.04 ≤ SEE ≤ 0.05 m · s^?1) with performance than the polynomially-derived equivalent (0.83 ≤ r ≤ 0.89; 0.10 ≤ SEE ≤ 0.13 m · s^?1). The exponential lactate threshold was greater than the polynomial equivalent (P < 0.05). The results suggest that the exponential lactate threshold is a valid performance index that is independent of the initial intensity of the incremental test and better than the polynomial equivalent.     

Salivary and plasma cortisol and testosterone responses to interval and tempo runs and a bodyweight-only circuit session in endurance-trained men

Abstract

The aim of this study was to examine the acute response to plasma and salivary cortisol and testosterone to three training protocols. Ten trained endurance athletes participated in three experimental trials, such as interval training (INT), tempo run (TEMP) and bodyweight-only circuit training (CIR), on separate days. Blood and saliva samples were collected pre- and 0, 15, 30 and 60 min post-exercise. Peak post-exercise salivary cortisol was higher than pre-exercise in all trials (P < 0.01). After INT, salivary cortisol remained elevated above pre-exercise than 60 min post-exercise. Salivary testosterone also increased post-exercise in all trials (P < 0.05). Plasma and salivary cortisol were correlated between individuals (r = 0.81, 0.73–0.88) and within individuals (r = 0.81, 0.73–0.87) (P < 0.01). Plasma and salivary testosterone was also correlated between (r = 0.57, 0.43–0.69) and within individuals (r = 0.60, 0.45–0.72), (P < 0.01). Peak cortisol and testosterone levels occurred simultaneously in plasma and saliva, but timing of post-exercise hormone peaks differed between trials and individuals. Further investigation is required to identify the mechanisms eliciting an increase in hormones in response to CIR. Furthermore, saliva is a valid alternative sampling technique for measurement of cortisol, although the complex, individual and situation dependent nature of the hormone response to acute exercise should be considered.     

Differences in lower-limb coordination and coordination variability between novice and experienced runners during a prolonged treadmill run at anaerobic threshold speed

This study investigated differences in lower-limb coordination and coordination variability between experienced and novice runners during a prolonged run. Thirty-four participants were categorised as either experienced (n = 17) or novice runners (n = 17). All participants performed a 31-min treadmill run at their individual anaerobic threshold speed, and lower-limb kinematic data were acquired in the sagittal plane at the beginning, middle, and end of the run. Lower-limb coordination and variability during the stance phase were quantified using a vector coding technique for hip-knee, knee-ankle, pelvis-thigh, thigh-shank, and shank-foot couplings. Repeated-measure analysis of covariance revealed that running experience and time had significant interactions on the coordination patterns for hip-knee and pelvis-thigh couplings. During the midstance, experienced runners exhibited a higher percentage of in-phase motion for pelvis-thigh and knee-ankle couplings while novice runners displayed a higher percentage of distal motion for pelvis-thigh coupling and anti-phase motion for hip-knee coupling. Experienced runners displayed more variability in hip-knee and shank-foot couplings, and novice runners had more variability in hip, knee, and thigh motion. Experienced and novice runners adapted to progressive fatigue through different lower-limb coordination patterns. Throughout the prolonged run, experienced runners demonstrated greater coordination variability and novice runners displayed greater joint and segment variability.     

Control of impact loading during distracted running before and after gait retraining in runners

Gait retraining using visual biofeedback has been reported to reduce impact loading in runners. However, most of the previous studies did not adequately examine the level of motor learning after training, as the modified gait pattern was not tested in a dual-task condition. Hence, this study sought to compare the landing peak positive acceleration (PPA) and vertical loading rates during distracted running before and after gait retraining. Sixteen recreational runners underwent a two-week visual biofeedback gait retraining program for impact loading reduction, with feedback on the PPA measured at heel. In the evaluation of PPA and vertical loading rates before and after the retraining, the participants performed a cognitive and verbal counting task while running. Repeated measures ANOVA indicated a significant interaction between feedback and training on PPA (F = 4.642; P = 0.048) but not vertical loading rates (F > 1.953; P > 0.067). Pairwise comparisons indicated a significantly lower PPA and vertical loading rates after gait retraining (P < 0.007; Cohen’s d > 0.68). Visual feedback after gait retraining reduced PPA and vertical loading rates during distracted running (P < 0.033; Cohen’s d > 0.36). Gait retraining is effective in lowering impact loading even when the runners are distracted. In dual-task situation, visual biofeedback provided beneficial influence on kinetics control after gait retraining.     

Effect of a marathon run on serum lipoproteins, creatine kinase, and lactate dehydrogenase in recreational runners

The objective of this study was to determine the effect of a marathon run on serum lipid and lipoprotein concentrations and serum muscle enzyme activities and follow their recovery after the run. These blood concentrations were measured before, immediately after, and serially after a marathon run in 15 male recreational runners. The triglyceride level was significantly elevated postrace, then fell 30% below baseline 1 day after the run, and returned to baseline after 1 week. Total cholesterol responded less dramatically but with a similar pattern. High-density lipoprotein cholesterol remained significantly elevated and low-density lipoprotein cholesterol was transiently reduced for 3 days after the run. The total cholesterol/high-density cholesterol ratio was significantly lowered for 3 days. Serum lactate dehydrogenase activity significantly doubled postrace and then declined but remained elevated for 2 weeks. Serum creatine kinase activity peaked 24 hr after the run, with a 15-fold rise, and returned to baseline after 1 week. The rise of these enzymes reflects mechanically damaged muscle cells leaking contents into the interstitial fluid. It is concluded that a prolonged strenuous exercise bout in recreational runners, such as a marathon, produces beneficial changes in lipid blood profiles that are significant for only 3 days. However, muscle damage is also evident for 1 week or more from the dramatic and long-lasting effect on enzyme levels. Laboratory values for these runners were outside normal ranges for some days after the race.     

Effect of resistance training regimens on treadmill running and neuromuscular performance in recreational endurance runners

Abstract

The purpose of this study was to assess the effects of heavy resistance, explosive resistance, and muscle endurance training on neuromuscular, endurance, and high-intensity running performance in recreational endurance runners. Twenty-seven male runners were divided into one of three groups: heavy resistance, explosive resistance or muscle endurance training. After 6 weeks of preparatory training, the groups underwent an 8-week resistance training programme as a supplement to endurance training. Before and after the 8-week training period, maximal strength (one-repetition maximum), electromyographic activity of the leg extensors, countermovement jump height, maximal speed in the maximal anaerobic running test, maximal endurance performance, maximal oxygen uptake ([Vdot]O_2max), and running economy were assessed. Maximal strength improved in the heavy (P = 0.034, effect size ES = 0.38) and explosive resistance training groups (P = 0.003, ES = 0.67) with increases in leg muscle activation (heavy: P = 0.032, ES = 0.38; explosive: P = 0.002, ES = 0.77). Only the heavy resistance training group improved maximal running speed in the maximal anaerobic running test (P = 0.012, ES = 0.52) and jump height (P = 0.006, ES = 0.59). Maximal endurance running performance was improved in all groups (heavy: P = 0.005, ES = 0.56; explosive: P = 0.034, ES = 0.39; muscle endurance: P = 0.001, ES = 0.94), with small though not statistically significant improvements in [Vdot]O_2max (heavy: ES = 0.08; explosive: ES = 0.29; muscle endurance: ES = 0.65) and running economy (ES in all groups < 0.08). All three modes of strength training used concurrently with endurance training were effective in improving treadmill running endurance performance. However, both heavy and explosive strength training were beneficial in improving neuromuscular characteristics, and heavy resistance training in particular contributed to improvements in high-intensity running characteristics. Thus, endurance runners should include heavy resistance training in their training programmes to enhance endurance performance, such as improving sprinting ability at the end of a race.     

Prediction of maximal oxygen uptake from a 20-m shuttle run as measured directly in runners and squash players

Abstract

The aim of this study was to assess the validity of the multistage shuttle run test in predicting maximal oxygen uptake (VO ₂ max) in athletes trained in sports with different physical demands. Over a 14-day period, 10 male long-distance runners (continuous high-intensity exercise) and 10 male squash players (intermittent high-intensity exercise) performed, in random order, the multistage shuttle run test and a maximal treadmill protocol of increasing elevation which elicited VO ₂ max. Compared with direct measurement of VO ₂ max, the shuttle run test significantly underpredicted the VO ₂ max of the group of runners (n=10; P<0.01) and of the athletes as a whole (n=20; P<0.01). The correlation (r) between VO ₂ max determined by the shuttle run test and by the treadmill protocol was 0.61 (P<0.05) for the squash players, 0.71 (P<0.05) for the runners and 0.67 (P<0.01) for the athletes as a whole. As the subjects represented athletes trained specifically in sports with different physical demands, this may explain why the correlations between the shuttle run test and direct measurement of VO ₂ max are less robust than those reported in previous studies. Furthermore, our results indicate that there are sport-specific differences when predicting VO ₂ max from the multistage shuttle run test.     

Influence of shod/unshod condition and running speed on foot-strike patterns,inversion/eversion,and vertical foot rotation in endurance runners

The aim of this study was to determine the influence of barefoot running on foot-strike patterns, eversion–inversion, running speed and vertical foot rotation in endurance runners. Eighty healthy recreational runners (age = 34.11 ± 12.95 years old, body mass index = 22.56 ± 2.65 kg · m^?2) performed trials in shod/unshod running conditions on a treadmill at comfortable and competitive self-selected speeds. Data were collected by systematic observation of lateral and back recordings at 240 Hz. McNemar’s test indicated significant differences between shod/unshod conditions and foot strike at comfortable and competitive speeds (P < 0.001). Speed was related to vertical foot rotation type for shod (P < 0.01) and unshod conditions (P < 0.05). Significant differences were found between shod/unshod conditions in foot rotation at comfortable running speeds (P < 0.001) and competitive running speeds (P < 0.01). No significant difference was found in inversion or eversion (P ≥ 0.05). In conclusion, the results suggest that running kinematics, in terms of foot-strike patterns and vertical foot rotation, differ between shod/unshod conditions, while the inversion or eversion degree remains unchanged.     

大学生冬季长跑活动耐力增长的“胡克”现象分析

本文通过文献资料法、专家访谈法、数理统计法对我省8所高校的学生进行了4个月的冬季长跑活动实验,一组采用每天1500M跑（4个月累计180KM）,一组按既定模式正常体育教学。实验结果发现两个不同形式体育练习的群体耐力有很大区别：实验组学生的耐力素质明显好于既定模式正常体育教学的学生,实验组学生耐力素质的增长遵循“胡克”定律（Hook’slaw,F=KX）。     

Kinetic changes during a six-week minimal footwear and gait-retraining intervention in runners

An evaluation of a six-week Combined minimal footwear transition and gait-retraining combination vs. gait retraining only on impact characteristics and leg stiffness. Twenty-four trained male runners were randomly assigned to either (1) Minimalist footwear transition Combined with gait-retraining over a six-week period (“Combined” group; n = 12) examined in both footwear, or (2) a gait-retraining group only with no minimalist footwear exposure (“Control”; n = 12). Participants were assessed for loading rate, impact peak, vertical, knee and ankle stiffness, and foot-strike using 3D and kinetic analysis. Loading rate was significantly higher in the Combined group in minimal shoes in pre-tests compared to a Control (P ≤ 0.001), reduced significantly in the Combined group over time (P ≤ 0.001), and was not different to the Control group in post-tests (P = 0.16). The impact peak (P = 0.056) and ankle stiffness reduced in both groups (P = 0.006). Loading rate and vertical stiffness was higher in minimalist footwear than conventional running shoes both pre (P ≤ 0.001) and post (P = 0.046) the intervention. There has a higher tendency to non-rearfoot strike in both interventions, but more acute changes in the minimalist footwear. A Combined intervention can potentially reduce impact variables. However, higher loading rate initially in minimalist footwear may increase the risk of injury in this condition.     

辽宁省中长跑运动员运动损伤的调查分析

运用文献资料法、问卷调查法、专家访谈法、数理统计法等,对中长跑运动员常见运动损伤的部位、损伤类型、损伤原因进行调查分析,并针对损伤的状况提出了预防措施及建议,以期为广大体育工作者进行中长跑教学和训练提供参考。     

Influence of recovery intensity on time spent at maximal oxygen uptake during an intermittent session in young,endurance-trained athletes

Abstract

In this study, we examined the effects of three recovery intensities on time spent at a high percentage of maximal oxygen uptake (t90[Vdot]O_2max) during a short intermittent session. Eight endurance-trained male adolescents (16 ± 1 years) performed four field tests until exhaustion: a graded test to determine maximal oxygen uptake ([Vdot]O_2max; 57.4 ± 6.1 ml · min^?1 · kg^?1) and maximal aerobic velocity (17.9 ± 0.4 km · h^?1), and three intermittent exercises consisting of repeat 30-s runs at 105% of maximal aerobic velocity alternating with 30 s active recovery at 50% (IE₅₀), 67% (IE₆₇), and 84% (IE₈₄) of maximal aerobic velocity. In absolute values, mean t90[Vdot]O_2max was not significantly different between IE₅₀ and IE₆₇, but both values were significantly longer compared with IE₈₄. When expressed in relative values (as a percentage of time to exhaustion), mean t90[Vdot]O_2max was significantly higher during IE₆₇ than during IE₅₀. Our results show that both 50% and 67% of maximal aerobic velocity of active recovery induced extensive solicitation of the cardiorespiratory system. Our results suggest that the choice of recovery intensity depends on the exercise objective.     

Relationship between physiological parameters and performance during a half-ironman triathlon in the heat

Abstract

Triathlon is a popular outdoor endurance sport performed under a variety of environmental conditions. The aim of this study was to assess physiological variables before and after a half-ironman triathlon in the heat and to analyse their relationship with performance. Thirty-four well-trained triathletes completed a half-ironman triathlon in a mean dry temperature of 29 ± 3ºC. Before and within 1 min after the end of the race, body mass, core temperature, maximal jump height and venous blood samples were obtained. Mean race time was 315 ± 40 min, with swimming (11 ± 1%), cycling (49 ± 2%) and running (40 ± 3%) representing different amounts of the total race time. At the end of the competition, body mass changed by ?3.8 ± 1.6% and the change in body mass correlated positively with race time (r = 0.64; P < 0.001). Core temperature increased from 37.5 ± 0.6ºC to 38.8 ± 0.7ºC (P < 0.001) and post-race core temperature correlated negatively with race time (r = ?0.47; P = 0.007). Race time correlated positively with the decrease in jump height (r = 0.38; P = 0.043), post-race serum creatine kinase (r = 0.55; P = 0.001) and myoglobin concentrations (r = 0.39; P = 0.022). In a half-ironman triathlon in the heat, greater reductions in body mass and higher post-competition core temperatures were present in faster triathletes. In contrast, slower triathletes presented higher levels of muscle damage and decreased muscle performance.     

The influence of performance level,age and gender on pacing strategy during a 100-km ultramarathon

The aim of this study is to analyse the influence of performance level, age and gender on pacing during a 100-km ultramarathon. Results of a 100-km race incorporating the World Masters Championships were used to identify differences in relative speeds in each 10-km segment between participants finishing in the first, second, third and fourth quartiles of overall positions (Groups 1, 2, 3 and 4, respectively). Similar analyses were performed between the top and bottom 50% of finishers in each age category, as well as within male and female categories. Pacing varied between athletes achieving different absolute performance levels. Group 1 ran at significantly lower relative speeds than all other groups in the first three 10-km segments (all P < 0.01), and significantly higher relative speeds than Group 4 in the 6th and 10th (both P < 0.01), and Group 2 in the 8th (P = 0.04). Group 4 displayed significantly higher relative speeds than Group 2 and 3 in the first three segments (all P < 0.01). Overall strategies remained consistent across age categories, although a similar phenomenon was observed within each category whereby ‘top’ competitors displayed lower relative speeds than ‘bottom’ competitors in the early stages, but higher relative speeds in the later stages. Females showed lower relative starting speeds and higher finishing speeds than males. ‘Top’ and ‘bottom’ finishing males displayed differing strategies, but this was not the case within females. Although pacing remained consistent across age categories, it differed with level of performance within each, possibly suggesting strategies are anchored on direct competitors. Strategy differs between genders and differs depending on performance level achieved in males but not females.     

Influence of shoe drop on running kinematics and kinetics in female runners

Abstract

This study investigated the effects of shoe drop on lower limb kinematics and kinetics in female runners.

Fifteen healthy female runners ran on a 15-m runway at their preferred speed with three different shoe-drop conditions: 0 (D₀), 6 (D₆) and 10 (D₁₀) mm. Three-dimensional marker positions and ground reaction forces were recorded to analyse kinetic and kinematic parameters using zero- (0D) and one-dimensional (1D) metrics (statistical parametric mapping, SPM). Regarding 0D parameters, significantly higher loading rates and transient peaks were found in D₀ compared to D₆ and D₁₀ conditions (both p?<?.01). For 1D analysis, significantly higher ankle dorsiflexion moments were found in D₀ compared to D₆ and D₁₀ during the braking phase (p?<?.01). Lower knee extension moments between 52% and 55% and 61% and 65% of contact time (p?<?.05) were also found. No difference was found between D₆ and D₁₀ conditions (p?>?.05). As previously shown in men, this study demonstrates that shoe drop influences running kinematic and kinetic patterns. Using SPM analysis in conjunction with classical analysis, the study adds new understanding on the influence of shoes on joint moment during contact time.     

耐力素质在现代竞技运动中的作用、影响因素及对策

对耐力素质在现代竞技运动中的作用、影响因素及对策进行了较深层次的研究，三大运动素质之一的耐力素质在运动训练中具有基础性的作用，与各个运动项目密切相关。     

论中长跑运动员身体素质训练的理论与方法

本文参考了大量的文献资料，收集了有关专家对中长跑运动员身体素质训练理论与方法的研究成果，对中长跑运动员身体素质训练理论与方法进行了综合归类、分析和研究，研究目的在于丰富中长跑运动员身体素质训练的理论与方法，为我国教练员和运动员训练时保证质量、提高运动成绩提供科学的参考依据。