Level Running Research Articles

A single bout of downhill running attenuates subsequent level running-induced fatigue

Fatigue can be defined as exercise-induced strength loss. During running, fatigue can be partially explained by repetitive low-intensity eccentric contractions-induced muscle damage (EIMD). Previous studies showed that a bout of downhill running (DR) attenuated subsequent EIMD. Thus, we tested if a 30-min DR bout would attenuate fatigue induced by subsequent 60-min level running (LR). Twenty-seven male college students were randomly allocated to an experimental (EXP) or a control (CON) group. All participants performed LR on a treadmill at 70% of the velocity (vVO2peak) corresponding to peak oxygen uptake (VO2peak). Only EXP performed a 30-min DR (− 15%) on a treadmill at 70% vVO2peak fourteen days before LR. Indirect EIMD markers and neuromuscular function were assessed before, immediately and 48 h after DR and LR. Knee extension isometric peak torque (IPT) decreased (− 36.3 ± 26%, p < 0.05) immediately following DR with full recovery reached 48 h post-DR. Muscle soreness developed (p < 0.05) immediately (37 ± 25 mm) and 48 h (45 ± 26 mm) post-DR. IPT and rate of torque development (RTD) at late phases (> 150 ms) from the onset of muscle contraction decreased significantly (− 10.7 ± 6.1% and from − 15.4 to − 18.7%, respectively) immediately after LR for the CON group and remained below baseline values (− 5.6 ± 8.5% and from − 13.8 to − 14.9%, respectively) 48 h post-LR. However, IPT and late RTD were not significantly affected by LR for the EXP group, showing a group x time interaction effect. We concluded that a single DR bout can be used to attenuate fatigue induced by a LR performed fourteen days after.

Biomechanics of graded running: Part II-Joint kinematics and kinetics.

Compared to level running (LR), different strategies might be implemented by runners to cope with specific challenges of graded running at different speeds. The changes in joint kinetics and kinematics associated with graded running have been investigated, but their interactions with speed are unknown. Nineteen participants ran on an instrumented treadmill at five grades (0°, ±5° and±10°) and three speeds (2.50, 3.33 and 4.17m/s), while 3D motion and forces were recorded. Three speed×five-grade repeated-measures ANOVA was used to analyze kinetic and kinematic variables. A speed×grade interaction was observed for hip range of motion (ROM). Downhill running (DR) at fastest speed did not reduce ROM at the hip, compared to LR. Compared to LR, it was observed that the hip joint was responsible for a greater contribution of energy generation while running at the fastest speed at +10°. Speed×grade interactions were also observed for the energy absorption, peak moment, and peak power at the knee. Contrary to LR, running faster during UR did not require higher peak power at the knee. Finally, DR at the fastest speed did not increase peak negative power at the knee compared to LR. This study demonstrates that ankle, knee, and hip joint kinetics depend on speed and grade of running, while the effect of grade on joint kinematics was not substantially modulated by speed.

Biomechanics of graded running: Part I - Stride parameters, external forces, muscle activations.

Biomechanical alterations with graded running have only been partially quantified, and the potential interactions with running speed remain unclear. We measured spatiotemporal parameters, ground reaction forces, and leg muscle activations (EMG) in nineteen adults (10F/9M) running on an instrumented treadmills at 2.50, 3.33, and 4.17m·s-1 and 0, ±5°, and ±10°. Step frequency illustrated a significant speed×grade interaction (P<.001) and was highest (+3%) at the steepest grade (+10°) and fastest speed (4.17m·s-1 ) when compared to level running (LR) at the same speed. Significant interaction was also observed for ground reaction forces (all P≤.047). Peak ground reaction forces in the normal direction increased with running speed during downhill running (DR) only (+9% at -10° and 4.17m·s-1 ). Impulse in the normal direction decreased at fastest speed and steepest DR (-9%) and uphill running (UR) (-17%) grades. Average normal loading rate increased and decreased at fastest speed and steepest DR (+52%) and UR (-28%) grades, respectively. Negative parallel impulse increased and decreased at fastest speed and steepest DR (+166%) and UR (-90%), respectively. Positive parallel impulse decreased and increased at fastest speed and steepest DR (-75%) and UR (+111%), respectively. EMG showed comparable u-shaped curves across the grades investigated, although only a change in vastus lateralis and tibilias anterior activity was detectable at the steepest grades and fastest speed. Overall, running grade and speed significantly influences spatiotemporal parameters, ground reaction forces, and muscle activations.

Trail Runners Cannot Reach V˙O2max during a Maximal Incremental Downhill Test.

The purpose of this study was twofold: (i) determine if well-trained athletes can achieve similar peak oxygen uptake (V˙O2peak) in downhill running (DR) versus level running (LR) or uphill running (UR) and (ii) investigate if lower limb extensor muscle strength is related to the velocity at V˙O2peak (vV˙O2peak) in DR, LR, and UR. Eight athletes (V˙O2max = 68 ± 2 mL·min·kg) completed maximal incremental tests in LR, DR (-15% slope), and UR (+15% slope) on a treadmill (+1, +1.5, and +0.5 km·h every 2 min, respectively) while cardiorespiratory responses and spatiotemporal running parameters were continuously measured. They were also tested for maximal voluntary isometric strength of hip and knee extensors and plantar flexors. Oxygen uptake at maximal effort was approximately 16% to 18% lower in DR versus LR and UR (~57 ± 2 mL·min·kg, 68 ± 2 mL·min·kg, and 70 ± 3 mL·min·kg, respectively) despite much greater vV˙O2peak (22.7 ± 0.6 km·h vs 18.7 ± 0.5 km·h and 9.3 ± 0.3 km·h, respectively). At vV˙O2peak, longer stride length and shorter contact time occurred in DR versus LR and UR (+12%, +119%, -38%, and -61%, respectively). Contrary to knee extensor and plantar flexor, hip extensor isometric strength correlated to vV˙O2peak in DR, LR, and UR (r = -0.86 to -0.96, P < 0.05). At similar V˙O2, higher heart rate and ventilation emerged in DR versus LR and UR, associated with a more superficial ventilation pattern. This study demonstrates that well-trained endurance athletes, accustomed to DR, achieved lower V˙O2peak despite higher vV˙O2peak during DR versus LR or UR maximal incremental tests. The specific heart rate and ventilation responses in DR might originate from altered running gait and increased lower-limb musculotendinous mechanical loading, furthering our understanding of the particular physiology of DR, ultimately contributing to optimize trail race running performance.

Cadence impact on cardiopulmonary, metabolic and biomechanical loading during downhill running

BackgroundDistance runners can approach long descents with slow cadence and long steps, or a fast cadence with shorter steps. These approaches differentially affect mechanical loading and energy demand. Research questionThis study determined the cadence range in which biomechanical loads, caloric unit cost and energy cost were simultaneously minimized during downhill running (DR). MethodsTrained runners (N = 40; 25.6 ± 7.2 yr; 42.5% female) participated in this experimental study. Participants ran on an instrumented treadmill while wearing a portable gas analyzer during six conditions: control normal level running (LR) at 0 deg inclination (CON-0); control DR -6 deg inclinaton (CON-6); DR at cadences +/-5% and +/-10% different from CON-6. A motion analysis system was used to capture running motion, and an instrumented treadmill captured force data. Cardiopulmonary measures, rating of perceived exertion (RPE), and biomechanical measures (temporal spatial parameters, peak ground reaction forces [GRF], vertical average loading rate [VALR], impulses) were calculated. Caloric unit cost and energy costs were standardized per unit distance. ResultsRunning at -10% cadence increased HR by 10 bpm compared to CON-6 (p < 0.0001). Vertical excursion of the center of mass and step length were greatest in the cadence -10% and least in the cadence +10% conditions (both p < 0.0001). RPEs were higher among all cadence conditions compared to CON-0 (p < 0.0001). Caloric unit costs were lowest in CON-6, and +/5% cadence conditions compared to the CON-0 and +/-10% conditions (-2.1% to -12.3%, respectively; p < 0.05). Peak GRF and VALR were not different among conditions; vertical impulses were greatest in the -10% condition compared to CON-0, CON-6 and +5% and +10% by 11.3–14.5% (p < .001). SignificanceChanging cadence across level and downhill stretches is likely not necessary and may actually increase perceived effort of running. Running downhill at cadences that range +/-5% of preferred simultaneously minimize caloric unit cost and impulse loading.

Irisin response to downhill running exercise in humans.

[Purpose]To determine the effects of exercise-induced muscle damage, we examined irisin responses during level running (LR), with less muscle damage, and downhill running (DHR), with greater muscle damage under equivalent exercise duration and oxygen consumption (⩒O2) conditions.[Methods]Fifteen healthy men (age: 21.6 ± 2.0 y, height: 170 ± 1.3 cm, weight: 64.8 ± 2.7 kg) were randomly assigned to either the LR group (n = 8) or the DHR group (n = 7). Subjects in the LR group performed treadmill running at 70% of maximum oxygen uptake (⩒O2max) for 30 min on a 0% gradient. In contrast, subjects in the DHR group performed the same exercise on a –10% gradient. Blood samples were collected before exercise, immediately after exercise, and 1, 3, and 24 h after exercise.[Results]No significant interaction (group × time) or main effect of group or time was observed for changes in plasma irisin concentrations over time (P > 0.05). However, the area under the curve of plasma irisin concentrations during a 3-h post-exercise period was significantly greater in the DHR (239,197 ± 8,166 ng/mL) group than in the LR (92,293 ± 8,755 ng/ml) group (P < 0.05). The blood lactate, serum cortisol, myoglobin, and plasma interleukin-6 concentrations were significantly higher in the DHR group than in the LR group after exercise (P < 0.05 for all variables).[Conclusion]DHR associated with marked muscle damage promoted a greater increase in exercise-induced irisin did LR after the same duration under identical VO2 conditions.

Biomechanics and Physiology of Uphill and Downhill Running.

Most running studies have considered level running (LR), yet the regulation of locomotor behaviour during uphill (UR) and downhill (DR) running is fundamental to increase our understanding of human locomotion. The purpose of this article was to review the existing literature regarding biomechanical, neuromuscular and physiological adaptations during graded running. Relative to LR, UR is characterized by a higher step frequency, increased internal mechanical work, shorter swing/aerial phase duration, and greater duty factor, while DR is characterized by increased aerial time, reduced step frequency and decreased duty factor. Grade also modifies foot strike patterns, with a progressive adoption of a mid- to fore-foot strike pattern during UR, and rear-foot strike patterns during DR. In UR, lower limb muscles perform a higher net mechanical work compared to LR and DR to increase the body's potential energy. In DR, energy dissipation is generally prevalent compared to energy generation. The increased demands for work as running incline increases are met by an increase in power output at all joints, particularly the hip. This implies that UR requires greater muscular activity compared to LR and DR. Energy cost of running (C r) linearly increases with positive slope but C r of DR decreases until a minimum slope is reached at -20%, after which C r increases again. The effects of slope on biomechanics, muscle contraction patterns and physiological responses have important implications for injury prevention and success of athletes engaged in graded running competitions.

Inter-segment foot kinematics during cross-slope running

Cross-slopes are a common terrain characteristic, however there is no biomechanical knowledge of the intra-foot adaptations required for running on these surface inclinations. The purpose of this study was to evaluate the kinematic changes induced within the foot while running on a transversely inclined surface. A three-segment foot model distinguishing between the hindfoot, forefoot, and hallux was used for this purpose. Nine healthy experienced male runners volunteered to perform level (0°) and cross-slope (10°) running trials barefoot at a moderate speed. Multivariate analysis of variance (MANOVA) for repeated measures was used to analyze the kinematics of the hindfoot with respect to tibia (HF/TB), forefoot with respect to hindfoot (FF/HF), and hallux with respect to forefoot (HX/FF) during level running (LR), incline running up-slope (IRU), and incline running down-slope (IRD) conditions. In the sagittal plane, the FF/HF angle showed greater dorsiflexion at peak vertical force production (MaxFz) in IRD compared to LR (p=0.042). The HX/FF was significantly more extended during IRU than LR at foot strike (p=0.027). More importantly, frontal plane asymmetries were also found. HF/TB angles revealed greater inversion at foot strike followed by greater eversion at MaxFz for IRU compared to IRD (p=0.042 and p=0.018, respectively). For the FF/HF angle, maximum eversion was greater during IRD than LR (p=0.035). Data suggests that running on cross-slopes can induce substantial intra-foot kinematic adaptations, whether this represents a risk of injury to both recreational and professional runners remains to be determined.

Comparison of lower limb muscle activation during downhill, level and uphill running

We compared the lower limb muscle activation during uphill running (UR), level running (LR), and downhill running (DR). Eight male physically active subjects ran three slopes for 30 min at the given speed (55% vVO2peak at LR), including DR ( 6 � ), LR (0 � ), and UR (6 � ) in a random crossover, repeated measures design. Electromyographic (EMG) signals were collected from the dominated lower limb muscles: rectus femoris (RF), biceps femoris (BF), gastrocnemius (GAS), soleus, and tibialis anterior. Our results showed that greater EMG of RF was found with inclining slope (UR>LR>DR, p DR>LR (p < 0.05). We concluded that significant differences regarding muscle activations among DR, LR, and UR were observed for the RF, BF, and GAS, especially when running opposing slopes (DR vs. UR). Additionally, when running toward uphill, the propulsive muscles, such as the RF and GAS seemed to exert more effort. In contrast, while running toward downhill, RF might work as an extensor muscle that was activated to a lesser extent, possi bly due to its undergoing eccentric movement.

Muscle activities of the lower limb during level and uphill running

This study aimed to compare the muscle activities of the lower limb during overground level running (LR) and uphill running (UR) by using a musculoskeletal model. Six male distance runners ran at three running speeds (slow: 3.3 m/s; medium: 4.2 m/s; and high: 5.0 m/s) on a level runway and a slope of 9.1% grade in which force platforms were mounted. A musculoskeletal leg model and optimization were used to estimate the muscle activation and muscle torque from the joint torque of the lower limb calculated by the inverse dynamics approach. At high speed, the activation and muscle torque of the muscle groups surrounding the hip joints, such as the hamstrings and iliopsoas, during the recovery phase were significantly greater during UR than during LR. At all the running speeds, the knee extension torque by the vasti during the support phase was significantly smaller during UR. Further, the hip flexion and knee extension torques by the rectus femoris during UR were significantly greater than those during LR at all the speeds; this would play a role in compensating for the decrease in the knee extension torque by the vasti and in maintaining the trunk in a forward-leaning position. These results revealed that the activation and muscle torque of the hip extensors and flexors were augmented during UR at the high speed.

EFFECTS OF BELOW AND ABOVE ANKLE ORTHOSES ON GAIT STABILTY IN PARTIAL FOOT AMPUTEES

This study aimed to compare the muscle activities of the lower limb during overground level running (LR) and uphill running (UR) by using a musculoskeletal model. Six male distance runners ran at three running speeds (slow: 3.3 m/s; medium: 4.2 m/s; and high: 5.0 m/s) on a level runway and a slope of 9.1% grade in which force platforms were mounted. A musculoskeletal leg model and optimization were used to estimate the muscle activation and muscle torque from the joint torque of the lower limb calculated by the inverse dynamics approach. At high speed, the activation and muscle torque of the muscle groups surrounding the hip joints, such as the hamstrings and iliopsoas, during the recovery phase were significantly greater during UR than during LR. At all the running speeds, the knee extension torque by the vasti during the support phase was significantly smaller during UR. Further, the hip flexion and knee extension torques by the rectus femoris during UR were significantly greater than those during LR at all the speeds; this would play a role in compensating for the decrease in the knee extension torque by the vasti and in maintaining the trunk in a forward-leaning position. These results revealed that the activation and muscle torque of the hip extensors and flexors were augmented during UR at the high speed.

Stance phase knee and ankle kinematics and kinetics during level and downhill running

To study possible mechanisms for muscle soreness in downhill running, ground reaction force and kinematic data were collected on seven male runners during 4.5 m.s-1 level running (LR) and 8.3% downhill grade running (DR). For DR, a force platform was mounted on a sloped concrete block flush with the surface of a ramp. A two-dimensional link segment model was used to calculate net stance phase moments for the knee and ankle. Data were averaged over all subjects for each condition. There was no significant difference (P less than 0.05) between DR and LR for peak flexion velocity, peak extensor moment, or peak power absorption at the knee. Negative work done on the extensor muscles of the knee during stance was significantly greater for DR (58.0 +/- 13 J) than for LR (30.0 +/- 9.0 J). Peak ankle power absorption was significantly greater for DR (619 +/- 85 W) than for LR (396 +/- 180 W). The negative work done on the extensor muscles of the ankle during stance was significantly greater for DR (26.1 +/- 3.2 J) than for LR (12.6 +/- 6.6 J). The results suggest that muscle soreness during DR may be related to high peak power absorption values since the peak joint extensor moments are similar between conditions.