Effect of downhill running grade on lower extremity loading in female distance runners

ABSTRACT

Hill running is often used as a foundational training mechanism to build strength and speed. Distance runners in particular are at an increased likelihood of encountering steep hills during training runs. There is limited research regarding downhill running, and there is no research available on the biomechanics of females specifically during downhill running. The purpose of this study was to quantify the differences in loading when running downhill at different grades compared to a level surface in female distance runners to determine the potential risk for injury. Fifteen female distance runners (age: 23.5 ± 4.9 y), who ran 56.3 ± 20.9 km a week participated in this study. Participants ran on a force-instrumented treadmill at 4.0 m/s for 2 min at 0%, ?5%, ?10%, ?15%, and ?20% grades, with 5 min of rest between conditions. Study findings showed increased impact forces (p < 0.001), and increased loading rates (p < 0.001) with increasing downhill grades compared to level. These results indicate a significantly greater risk of overuse injury to the lower extremity with steeper downhill grades. Individuals need to be aware of these risks to plan and implement training programmes that will increase performance while minimising injury risk.     

中长跑运动员跑台跑与场地跑下肢肌肉工作情况的比较分析

目的:通过EMG记录分析跑台跑和场地跑肌肉用力情况特征,比较这两种状态跑时肌肉用力方式的各自特点。方法:11名中长跑运动员,每名运动员分两天测试,随机让其以10 km/h、12 km/h、14 km/h、16 km/h、18 km/h的速度在场地和跑台(0%、5%、10%坡度)运动6min,每种速度跑之间间歇10min。使用便携式Megawin ME-6000肌电仪记录其下肢肌群(臀大肌、股外侧肌、股二头肌、腓肠肌内侧头、胫骨前肌)EMG变化情况。结果表明:在肌肉用力方面,5%坡度的跑台跑可以模拟场地跑,而10%坡度的跑台跑则可以给予下肢肌群更强的刺激,以满足训练的需要;跑台跑时,胫骨前肌需要比在场地跑时动员更多的运动单位参与工作,而跑台的坡度和速度增加对动员更多的运动单位影响不大。     

Side-sloped surfaces substantially affect lower limb running kinematics

Running on side-sloped surfaces is a common obstacle in the environment; however, how and to what extent the lower extremity kinematics adapt is not well known. The purpose of this study was to determine the effects of side-sloped surfaces on three-dimensional kinematics of hip, knee, and ankle during stance phase of running. Ten healthy adult males ran barefoot along an inclinable runway in level (0°) and side-sloped (10° up-slope and down-slope inclinations, respectively) configurations. Right hip, knee, and ankle angles along with their time of occurrence were analysed using repeated measures MANOVA. Up-slope hip was more adducted (p = 0.015) and internally rotated (p = 0.030). Knee had greater external rotations during side-sloped running at heel-strike (p = 0.005), while at toe-off, it rotated externally and internally during up-slope and down-slope running, respectively (p = 0.001). Down-slope ankle had greatest plantar flexion (p = 0.001). Up-slope ankle had greatest eversion compared with down-slope (p = 0.043), while it was more externally rotated (p = 0.030). These motion patterns are necessary to adjust the lower extremity length during side-sloped running. Timing differences in the kinematic events of hip adduction and external rotation, and ankle eversion were observed (p = 0.006). Knowledge on these alterations is a valuable tool in adopting strategies to enhance performance while preventing injury.     

Water immersion as a recovery aid from intermittent shuttle running exercise

Abstract

Aim: To investigate the effect of different water immersion (WI) treatments on recovery from intermittent shuttle running exercise in comparison to an ecologically relevant control.

Methods: Forty males performed 90 minutes intermittent shuttle running, following which they were assigned to either: (1) 12-min standing WI at 12°C; (2) 12-min standing WI at 35°C; (3) 2-min seated WI at 12°C; (4) an ecologically relevant control consisting of 12 minutes walking at 5 km h^?1. Muscle soreness, maximal voluntary contraction (MVC) of the knee flexors and extensors, hop distance, creatine kinase activity and myoglobin concentration were measured before exercise and in the 168 hours following the intervention. Between-group differences, time effects and interaction effects were investigated by mixed-model ANOVA.

Results: The shuttle running exercise induced an increase in muscle soreness (1, 24, 48 and 72 hours post-intervention) creatine kinase activity and myoglobin concentration (post-exercise and 1, 24 and 48 hours post-intervention), and reduced MVC of the knee extensors (11% reduction at 24 hours, remaining reduced at 48 and 72 hours), flexors (24% reduction at 24 hours, remaining reduced at 24, 48, 72 and 168 hours), and hop distance (24 and 48 hours). However, no between-group differences or interaction effects were evident for any of these parameters.

Conclusion: The WI protocols investigated were not better than light exercise in facilitating recovery from shuttle running exercise. Future studies examining the efficacy of WI as a recovery intervention should include a representative control condition to increase their relevance to sporting populations.     

The efficacy of downhill running as a method to enhance running economy in trained distance runners

Running downhill, in comparison to running on the flat, appears to involve an exaggerated stretch-shortening cycle (SSC) due to greater impact loads and higher vertical velocity on landing, whilst also incurring a lower metabolic cost. Therefore, downhill running could facilitate higher volumes of training at higher speeds whilst performing an exaggerated SSC, potentially inducing favourable adaptations in running mechanics and running economy (RE). This investigation assessed the efficacy of a supplementary 8-week programme of downhill running as a means of enhancing RE in well-trained distance runners. Nineteen athletes completed supplementary downhill (?5% gradient; n?=?10) or flat (n?=?9) run training twice a week for 8 weeks within their habitual training. Participants trained at a standardised intensity based on the velocity of lactate turnpoint (vLTP), with training volume increased incrementally between weeks. Changes in energy cost of running (E_C) and vLTP were assessed on both flat and downhill gradients, in addition to maximal oxygen uptake (?O_2max). No changes in E_C were observed during flat running following downhill (1.22?±?0.09 vs 1.20?±?0.07?Kcal?kg^?1?km^?1, P?=?.41) or flat run training (1.21?±?0.13 vs 1.19?±?0.12?Kcal?kg^?1?km^?1). Moreover, no changes in E_C during downhill running were observed in either condition (P?>?.23). vLTP increased following both downhill (16.5?±?0.7 vs 16.9?±?0.6?km?h^?1 _, P?=?.05) and flat run training (16.9?±?0.7 vs 17.2?±?1.0?km?h^?1, P?=?.05), though no differences in responses were observed between groups (P?=?.53). Therefore, a short programme of supplementary downhill run training does not appear to enhance RE in already well-trained individuals.     

Lower limb joint angles and ground reaction forces in forefoot strike and rearfoot strike runners during overground downhill and uphill running

This study investigated the normal and parallel ground reaction forces during downhill and uphill running in habitual forefoot strike and habitual rearfoot strike (RFS) runners. Fifteen habitual forefoot strike and 15 habitual RFS recreational male runners ran at 3 m/s ± 5% during level, uphill and downhill overground running on a ramp mounted at 6° and 9°. Results showed that forefoot strike runners had no visible impact peak in all running conditions, while the impact peaks only decreased during the uphill conditions in RFS runners. Active peaks decreased during the downhill conditions in forefoot strike runners while active loading rates increased during downhill conditions in RFS runners. Compared to the level condition, parallel braking peaks were larger during downhill conditions and parallel propulsive peaks were larger during uphill conditions. Combined with previous biomechanics studies, our findings suggest that forefoot strike running may be an effective strategy to reduce impacts, especially during downhill running. These findings may have further implications towards injury management and prevention.     

The effects of protease supplementation on skeletal muscle function and DOMS following downhill running

Protease supplementation has been shown to attenuate soft tissue injury resulting from intense exercise. The aim of this study was to evaluate the effects of protease supplementation on muscle soreness and contractile performance after downhill running. Ten matched pairs of male participants ran at a ?10% grade for 30?min at 80% of their predicted maximal heart rate. The participants consumed two protease tablets (325?mg pancreatic enzymes, 75?mg trypsin, 50?mg papain, 50?mg bromelain, 10?mg amylase, 10?mg lipase, 10?mg lysozyme, 2?mg chymotrypisn) or a placebo four times a day beginning 1 day before exercise and lasting a total of 4 days. The participants were evaluated for perceived muscle soreness of the front and back of the dominant leg, pressure pain threshold by dolorimetry of the anterior medial, anterior lateral, posterior medial and posterior lateral quadrants of the thigh, and knee extension/flexion torque and power. The experimental group demonstrated superior recovery of contractile function and diminished effects of delayed-onset muscle soreness after downhill running when compared with the placebo group. Our results indicate that protease supplementation may attenuate muscle soreness after downhill running. Protease supplementation may also facilitate muscle healing and allow for faster restoration of contractile function after intense exercise.     

The effects of protease supplementation on skeletal muscle function and DOMS following downhill running

Protease supplementation has been shown to attenuate soft tissue injury resulting from intense exercise. The aim of this study was to evaluate the effects of protease supplementation on muscle soreness and contractile performance after downhill running. Ten matched pairs of male participants ran at a -10% grade for 30 min at 80% of their predicted maximal heart rate. The participants consumed two protease tablets (325 mg pancreatic enzymes, 75 mg trypsin, 50 mg papain, 50 mg bromelain, 10 mg amylase, 10 mg lipase, 10 mg lysozyme, 2 mg chymotrypisn) or a placebo four times a day beginning 1 day before exercise and lasting a total of 4 days. The participants were evaluated for perceived muscle soreness of the front and back of the dominant leg, pressure pain threshold by dolorimetry of the anterior medial, anterior lateral, posterior medial and posterior lateral quadrants of the thigh, and knee extension/flexion torque and power. The experimental group demonstrated superior recovery of contractile function and diminished effects of delayed-onset muscle soreness after downhill running when compared with the placebo group. Our results indicate that protease supplementation may attenuate muscle soreness after downhill running. Protease supplementation may also facilitate muscle healing and allow for faster restoration of contractile function after intense exercise.     

人参提取物达玛烷苷元对人体运动后肌糖原恢复的影响及机制研究

目的：给受试者服用不同浓度的人参提取物达玛烷苷元（Dammarane Sapogenin,DS）,探究其对有氧运动后肌糖原恢复的影响及作用机制。方法：本研究采用双盲实验设计,选取9名受试者随机分为安慰剂组（placebo group）、服用 DS 240 mg / day 组（DS240）、服用 DS 480 mg / day 组（DS480）进行试验。受试者持续服用 DS 4周后,进行一次性60分钟、强度为75%VO2 max 的蹬功率自行车运动,运动后立刻给予高糖饮食。于运动后即刻及运动后3小时,分别进行肌肉活检,测定 AKT、GS 磷酸化及蛋白质表达;同时,运动后3小时内每隔30分钟取静脉血测定血糖浓度、胰岛素浓度。结果：DS240组较对照组显著提升运动后肌糖原储存速率（P <0.05）;运动后随着时间延长,DS240组的血糖浓度显著低于安慰剂组（P <0.05）,但各组胰岛素浓度无显著性差异;运动后 DS240组显著提高运动后 AKT 磷酸化水平、降低肌糖原合成酶磷酸化、提高肌糖原合成酶的蛋白质表达（P <0.05）。结论：长期补充低剂量达玛烷苷元可能提高人体运动后肌糖原储存速率,其可能机制与提升胰岛素作用及血糖吸收有关;研究结果推测达玛烷苷元可以增加胰岛素敏感度,因而可以将达玛烷苷元作为补剂用以运动竞赛或训练后加速肌糖原恢复。     

Energy cost and kinematics of level,uphill and downhill running: fatigue-induced changes after a mountain ultramarathon

This study aimed to determine whether the fatigue induced by a mountain ultramarathon (MUM) led to changes in energy cost and kinematic during level and graded running. Pre- and post-race, 14 ultratrail runners ran on a level, uphill (5%) and downhill (5%) treadmill at 10 km · h^?1. Kinematic data were acquired using a photocell system. Post-race, the downhill energy cost increased by 13.1% (P < 0.001). No change was noted in level and uphill running. Duty factor and stride frequency were increased, whereas swing time, cycle time and stride length were decreased in all conditions (P < 0.05). Contact time was increased and the rate of force generation was decreased only in the uphill and downhill conditions (P < 0.05). Positive correlations were observed between performance time and the pre- to post-changes in the energy cost of level (r = 0.52, P = 0.04) and uphill running (r = 0.50, P = 0.04). MUM-induced fatigue resulted in physiological and spatiotemporal changes, though the response to fatigue varied considerably between running conditions. These changes resulted in a significant increment only in the downhill energy cost. Incorporating downhill locomotion in the training programmes of ultratrailers may help to improve performance-related physiological and biomechanical parameters.     

Influence of cold-water immersion on limb blood flow after resistance exercise*

This study determined the influence of cold (8°C) and cool (22°C) water immersion on lower limb and cutaneous blood flow following resistance exercise. Twelve males completed 4 sets of 10-repetition maximum squat exercise and were then immersed, semi-reclined, into 8°C or 22°C water for 10-min, or rested in a seated position (control) in a randomized order on different days. Rectal and thigh skin temperature, muscle temperature, thigh and calf skin blood flow and superficial femoral artery blood flow were measured before and after immersion. Indices of vascular conductance were calculated (flux and blood flow/mean arterial pressure). The colder water reduced thigh skin temperature and deep muscle temperature to the greatest extent (P?<?.001). Reductions in rectal temperature were similar (0.2–0.4°C) in all three trials (P?=?.69). Femoral artery conductance was similar after immersion in both cooling conditions, with both conditions significantly lower (55%) than the control post-immersion (P?<?.01). Similarly, there was greater thigh and calf cutaneous vasoconstriction (40–50%) after immersion in both cooling conditions, relative to the control (P?<?.01), with no difference between cooling conditions. These findings suggest that cold and cool water similarly reduce femoral artery and cutaneous blood flow responses but not muscle temperature following resistance exercise.     

Movement velocity as a measure of exercise intensity in three lower limb exercises

The purpose of this study was to investigate the relationship between movement velocity and relative load in three lower limbs exercises commonly used to develop strength: leg press, full squat and half squat. The percentage of one repetition maximum (%1RM) has typically been used as the main parameter to control resistance training; however, more recent research has proposed movement velocity as an alternative. Fifteen participants performed a load progression with a range of loads until they reached their 1RM. Maximum instantaneous velocity (V_max) and mean propulsive velocity (MPV) of the knee extension phase of each exercise were assessed. For all exercises, a strong relationship between V_max and the %1RM was found: leg press (r²_adj = 0.96; 95% CI for slope is [?0.0244, ?0.0258], P < 0.0001), full squat (r²_adj = 0.94; 95% CI for slope is [?0.0144, ?0.0139], P < 0.0001) and half squat (r²_adj = 0.97; 95% CI for slope is [?0.0135, ?0.00143], P < 0.0001); for MPV, leg press (r²_adj = 0.96; 95% CI for slope is [?0.0169, ?0.0175], P < 0.0001, full squat (r²_adj = 0.95; 95% CI for slope is [?0.0136, ?0.0128], P < 0.0001) and half squat (r²_adj = 0.96; 95% CI for slope is [?0.0116, 0.0124], P < 0.0001). The 1RM was attained with a MPV and V_max of 0.21 ± 0.06 m s^?1 and 0.63 ± 0.15 m s^?1, 0.29 ± 0.05 m s^?1 and 0.89 ± 0.17 m s^?1, 0.33 ± 0.05 m s^?1 and 0.95 ± 0.13 m s^?1 for leg press, full squat and half squat, respectively. Results indicate that it is possible to determine an exercise-specific %1RM by measuring movement velocity for that exercise.     

Motor unit firing frequency of lower limb muscles during an incremental slide board skating test

This study investigated how the combination of workload and fatigue affected the frequency components of muscle activation and possible recruitment priority of motor units during skating to exhaustion. Ten male competitive speed skaters performed an incremental maximal test on a slide board. Activation of six muscles from the right leg was recorded throughout the test. A time-frequency analysis was performed to compute overall, high, and low frequency bands from the whole signal at 10, 40, 70, and 90% of total test time. Overall activation increased for all muscles throughout the test (p < 0.05 and ES > 0.80). There was an increase in low frequency (90 vs. 10%, p = 0.035, ES = 1.06) and a decrease in high frequency (90 vs. 10%, p = 0.009, ES = 1.38, and 90 vs. 40%, p = 0.025, ES = 1.12) components of gluteus maximus. Strong correlations were found between the maximal cadence and vastus lateralis, gluteus maximus and gluteus medius activation at the end of the test. In conclusion, the incremental skating test lead to an increase in activation of lower limb muscles, but only gluteus maximus was sensitive to changes in frequency components, probably caused by a pronounced fatigue.     

Electromyographic analysis of lower limb muscles during the golf swing performed with three different clubs

The aim of this study was to describe and compare the EMG patterns of select lower limb muscles throughout the golf swing, performed with three different clubs, in non-elite middle-aged players. Fourteen golfers performed eight swings each using, in random order, a pitching wedge, 7-iron and 4-iron. Surface electromyography (EMG) was recorded bilaterally from lower limb muscles: tibialis anterior, peroneus longus, gastrocnemius medialis, gastrocnemius lateralis, biceps femoris, semitendinosus, gluteus maximus, vastus medialis, rectus femoris and vastus lateralis. Three-dimensional high-speed video analysis was used to determine the golf swing phases. Results showed that, in average handicap golfers, the highest muscle activation levels occurred during the Forward Swing Phase, with the right semitendinosus and the right biceps femoris muscles producing the highest mean activation levels relative to maximal electromyography (70–76% and 68–73% EMG_MAX, respectively). Significant differences between the pitching wedge and the 4-iron club were found in the activation level of the left semitendinosus, right tibialis anterior, right peroneus longus, right vastus medialis, right rectus femuris and right gastrocnemius muscles. The lower limb muscles showed, in most cases and phases, higher mean values of activation on electromyography when golfers performed shots with a 4-iron club.     

热环境对力竭游泳运动恢复期大鼠下丘脑细胞外液单胺类神经递质的影响

观察大鼠在热环境中进行力竭游泳运动后24h恢复期下丘脑细胞外液单胺类神经递质含量的动态变化,分析其变化特点与相互关系,为探索热环境下运动性中枢疲劳的产生和恢复机制提供实验依据。方法:将32只SD雄性大鼠随机分成常温安静组、常温力竭组、高温安静组、高温力竭组,采集运动后4h、5h、6h、8h及24h微透析样品,并采用毛细管电泳-激光诱导荧光法检测单胺类神经递质含量。结论:热环境下大鼠力竭运动恢复期下丘脑细胞外液5-羟色胺(5-HT)含量与常温力竭运动相比升高更加显著,介导核心温度的升高;而多巴胺(DA)和去甲肾上腺素(NE)含量的降低,导致机体对热的耐受性降低;高5-HT浓度、高核心温度和机体低热耐受性的共同作用,加快中枢疲劳的发生,降低机体运动能力。     

Neuromuscular,biomechanical, and energetic adjustments following repeated bouts of downhill running

Purpose:This study used downhill running as a model to investigate the repeated bout effect(RBE) on neuromuscular performance,running biomechanics,and metabolic cost of running.Methods:Ten healthy recreational male runners performed two 30-min bouts of downhill running(DR1 and DR2) at a-20% slope and 2.8 m/s3 weeks apart.Neuromuscular fatigue,level running biomechanics during slow and fast running,and running economy parameters were recorded immediately before and after the downhill bouts,and at...     

Changes in segment coordination variability and the impacts of the lower limb across running mileages in half marathons: Implications for running injuries

BackgroundSegment coordination variability (CV) is a movement pattern associated with running-related injuries. It can also be adversely affected by a prolonged run. However, research on this topic is currently limited. The purpose of this study was to investigate the effects of a prolonged run on segment CV and vertical loading rates during a treadmill half marathon.MethodsFifteen healthy runners ran a half marathon on an instrumental treadmill in a biomechanical laboratory. Synchronized kinematic and kinetic data were collected every 2 km (from 2 km until 20 km), and the data were processed by musculoskeletal modeling. Segment CVs were computed from the angle-angle plots of selected pelvis-thigh, thigh-shank, and shank-rearfoot couplings using a modified vector coding technique. The loading rate of vertical ground reaction force was also calculated. A one-way MANOVA with repeated measures was performed on each of the outcome variables to examine the main effect of running mileage.ResultsSignificant effects of running mileage were found on segment CVs (p ≤ 0.010) but not on loading rate (p = 0.881). Notably, during the early stance phase, the CV of pelvis frontal vs. thigh frontal was significantly increased at 20 km compared with the CV at 8 km (g = 0.59, p = 0.022). The CV of shank transverse vs. rearfoot frontal decreased from 2 km to 8 km (g = 0.30, p = 0.020) but then significantly increased at both 18 km (g = 0.05, p < 0.001) and 20 km (g = 0.36, p < 0.001).ConclusionAt the early stance, runners maintained stable CVs on the sagittal plane, which could explain the unchanged loading rate throughout the half marathon. However, increased CVs on the frontal/transverse plane may be an early sign of fatigue and indicative of possible injury risk. Further studies are necessary for conclusive statements in this regard.     

Orthotic control of rear foot and lower limb motion during running in participants with chronic Achilles tendon injury

This study examined the kinematic effects of orthoses in participants with a history of chronic Achilles tendon injury. Twelve participants ran at self-selected speeds on a treadmill with and without customized orthoses. Joint and segment angles including leg abduction, calcaneal, eversion, ankle dorsiflexion, and knee flexion angles were calculated from three-dimensional data throughout stance. Five footfalls were obtained for each participant and condition. Statistical tests revealed an increase in maximum eversion with orthoses (P < 0.001, eta(p)2 = 0.642). In the individual participant analysis, this was evident in 9 of 12 participants. Trends towards increased eversion range of motion and decreased ankle dorsiflexion maximum and range of motion angles were also observed. Increased eversion was unexpected as all devices were designed to provide pronation control as deemed necessary by the podiatrist. Despite this, participants reported between 50 and 100% (average 92%) relief from symptoms with the use of orthoses. Further analysis of the angle-time curves and coordination between angular measures is recommended.     

踢毽对中老年人下肢肌肉力量和伸展的影响

采用CybexⅡ^ 等速肌力测试系统对持续踢毽锻炼2年的广州市128名中老年人的膝关节屈、伸肌群力量进行标准化、定量化测量，结果表明：男、女屈、伸膝肌群耐力(ER)、爆发力(TAE)自身前后对照各项肌力指标均有显著性差异。