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Preferred step frequency during downhill running may be determined by muscle activity
Abstract
It is well established that metabolic cost is minimized at an individual's running preferred step frequency (PSF). It has been proposed that the metabolic minimum at PSF is due to a tradeoff between mechanical factors, however, this ignores muscle activity, the primary consumer of energy. Thus, we hypothesized that during downhill running, total muscle activity would be greater with deviations from PSF. Specifically, we predicted that slow step frequencies would have greater stance activity while fast step frequencies would have greater swing activity. We collected metabolic cost and leg muscle activity data while 10 healthy young adults ran at 3.0m/s for 5 min at level and downhill at PSF and ±15% PSF. In support of our hypothesis, there was a significant main effect for step frequency for both metabolic cost and total muscle activity. In addition, there was greater muscle activity in the stance phase during the slower step frequency while muscle activity was greater in the swing phase during the fast step frequency. This suggests that PSF is partially determined by the tradeoff between the greater cost of muscle activity in the swing phase and lower cost in the stance phase with faster step frequency.
... The RBE is generally reported in greater proportion through blood CK elevation than DOMS and post-exercise MVC force/torque decrement [190]. Chen et al. [92] also suggested a beneficial effect of a first DR bout on RE (expressed as V O 2 ; preserved up to 72 h post exercise) and stride parameters [46,63,67,68,85,92,121,141,143,165,181,184,185,192,193,196,197], preconditioning strategies [16,81], DR training [14,209,210,254], changes in stride pattern [32,67,68,218,219,221,220,228,255], the use of lower limb compression garments [15,236,237], and the use of specific footwear [28,149,253,256]. In a and b, orange, blue, red, purple, and green spheres correspond to isometric MVC force/torque loss, changes in running economy and mechanics, ultrastructural alterations, inflammation and oedema, and muscle soreness, respectively. ...
... In contrast, Eston et al. [67] observed no difference in plasma CK, MVC force and muscle tenderness after a 40-min intermittent DR (5 × 8-min; slope: − 12%; speed: 11.3 km h −1 ) in untrained participants, regardless of the foot stride manipulation tested. Regarding the impact of foot stride manipulation on running performance, Sheehan et al. [220] reported that foot stride manipulation can affect RE (expressed as energy cost) during DR (slope: − 10.5%; speed: 10.8 km h −1 ) with a lower energy cost reported with a preferred stride frequency (PSF) compared to understride (− 12% for 85% PSF) and overstride (− 6% for 115% PSF). Similar results, albeit not significant, were reported by Snyder and Farley [32] when PSF was compared to understride (− 17.4% vs. 85% PSF) and overstride (− 16.2% vs. 115% PSF) during DR at shallow negative slope and low running speed (− 5.2%; speed: 7.2 km h −1 ). ...
Downhill running (DR) is a whole-body exercise model that is used to investigate the physiological consequences of eccentric muscle actions and/or exercise-induced muscle damage (EIMD). In a sporting context, DR sections can be part of running disciplines (of-road and road running) and can accentuate EIMD, leading to a reduction in performance. The purpose of this narrative review is to: (1) better inform on the acute and delayed physiological effects of DR; (2) identify and discuss, using a comprehensive approach, the DR characteristics that affect the physiological responses to DR and their potential
interactions; (3) provide the current state of evidence on preventive and in-situ strategies to better adapt to DR. Key findings of this review show that DR may have an impact on exercise performance by altering muscle structure and function due to EIMD. In the majority of studies, EIMD are assessed through isometric maximal voluntary contraction, blood creatine kinase and delayed onset muscle soreness, with DR characteristics (slope, exercise duration, and running speed) acting as the main influencing factors. In previous studies, the median (25th percentile, Q1; 75th percentile, Q3) slope, exercise duration, and running speed were − 12% (− 15%; − 10%), 40 min (30 min; 45 min) and 11.3 km h−1 (9.8 km h−1; 12.9 km h−1), respectively. Regardless of DR characteristics, people the least accustomed to DR generally experienced the most EIMD. There is growing evidence to suggest that preventive strategies that consist of prior exposure to DR are the most effective to better tolerate DR. The effectiveness of in-situ strategies such as lower limb compression garments and specific footwear remains to be confirmed. Our review finally highlights important discrepancies between studies in the assessment of EIMD, DR protocols and populations, which prevent drawing firm conclusions on factors that most influence the response to DR, and adaptive strategies to DR.
... Et cette fréquence s'établit à 108% de la fréquence préférentielle, cela malgré une activité musculaire supérieure liée justement à cette augmentation de fréquence (Sheehan & Gottschall, 2013). De même, de manière anecdotique, Ehrström et al. ont montré une atténuation de la perception des douleurs et une réduction des altérations neuromusculaires périphériques post course en descente par le port de bas de compression à haute pression (Ehrstrom, Gruet, et al., 2018). ...
... Au niveau physiologique, la V O2 augmente de manière exponentielle avec l'augmentation de la pente positive et/ou de la vitesse de locomotion. Mais précisons que dans les cas de pentes extrêmes, le rendement en montée en termes de relation V O2/vitesse d'ascension incite à privilégier la pente importante à la vitesse dans les stratégies de déplacement (Giovanelli, Ortiz, Henninger, & Kram, 2016;Ortiz et al., 2017 (Sheehan & Gottschall, 2013;Vernillo, Giandolini, et al., 2017). Notons toutefois que dans cas de pentes extrêmes le pattern de course est abandonné pour celui de la marche. ...
Il est bien établi chez les physiologistes, que si l’exercice de course en montée sollicite préférentiellement des contractions musculaires concentriques, l’exercice de course en descente requiert des actions musculaires frénatrices, majoritairement excentriques. L’exercice de course en descente à intensité sous-maximale génère un stimulus mécanique plus important pour un niveau de sollicitation métabolique moindre (i.e., V̇O2). Basée sur 3 études expérimentales, cette thèse de doctorat explore la physiologie spécifique de la course en déclivité, ainsi que ses prédicteurs physiologiques. Notre première étude montre une amplitude des réponses cardiorespiratoires amoindrie, une ventilation plus superficielle et une composante lente négative de consommation d’oxygène et de fréquence cardiaque en course en descente versus montée à vitesse constante et identique (8,5 km·h-1, pente de 15%). Lors de tests incrémentaux maximaux en course en descente vs montée vs plat, notre 2ème, partie A étude démontre que des coureurs bien entraînés, familiarisés avec la course en descente, peuvent atteindre FCmax, mais pas V̇O2max en descente. Lorsque les courses en descente et montée sont réalisées à même intensité métabolique (70% V̇O2max), notre 2ème (B) étude démontre que la course en descente (19 km·h-1, pente de -15%) induit des réponses cardiorespiratoires supérieures (FC et V̇E), une composante lente de V̇O2 significative et engendre une fatigue supérieure à la course en montée (6 km·h-1, pente de +15%). Enfin, une étude de terrain (étude 3) montre que les performances de 5 km de course en montée et en descente partagent quelques prédicteurs physiologiques communs (V̇O2max, force musculaire des membres inférieurs), bien que dans des proportions différentes. De plus, ces deux contre-la-montre sont également déterminés par des prédicteurs physiologiques spécifiques (i.e., raideur musculo-tendineuse en descente et indice de masse corporelle en montée). Nos résultats améliorent notre compréhension de la physiologie spécifique à la course en descente vs montée et ouvrent la voie des applications à l’entraînement des traileurs avec le but ultime d’optimiser leur performance.
... Redfern and Di Pasquale [4] and Sheehan and Gottschall [5] demonstrated that the risk of falling and slipping is higher for downhill walking than for level and uphill walking. This increased injury risk is caused primarily by high loads on the lower extremities' joints [6,7]. ...
... The eccentric forces applied to the tissues of the knee, produce a higher knee load [6,7]. The combination of increased coordinative demand and joints' load might lead to pain and increase injury risk during downhill walking [5,4,8]. Furthermore, typically, the downhill phase of hiking follows the high intensity uphill phase. ...
... Redfern and Di Pasquale [4] and Sheehan and Gottschall [5] demonstrated that the risk of falling and slipping is higher for downhill walking than for level and uphill walking. This increased injury risk is caused primarily by high loads on the lower extremities' joints [6,7]. ...
... The eccentric forces applied to the tissues of the knee, produce a higher knee load [6,7]. The combination of increased coordinative demand and joints' load might lead to pain and increase injury risk during downhill walking [5,4,8]. Furthermore, typically, the downhill phase of hiking follows the high intensity uphill phase. ...
Hiking is a backcountry activity suitable for people in every age. Pain and injuries are reported in hiking especially during downhill walking. This increased injury risk is caused primarily by high loads on the lower extremities’ joints and the optimal coordination control therefore required. Through the use of knee supports during hiking the injury risk might be reduced by, for example, improving proprioception. The purpose of this study was to determine the effect of wearing a knee sleeve and a knee brace on knee proprioception during a hiking simulation protocol on a treadmill. Twenty-four female sport students took part in this study. Joint position sense was measured without wearing any knee support, wearing a knee sleeve and wearing a knee brace at the beginning, after 30 minutes uphill walking and after 30 min downhill walking on a treadmill. Considering all tested subjects, without knee support the absolute repositioning error at the beginning was signifcantly better than the error after downhill walking (p=0.022) but no effect of the knee supports was found. Analysing only the subjects with a worsening in joint position sense after the activity, a signifcant improvement in joint position sense found wearing the sleeve and the brace after uphill and downhill walking (p<0.05).
... When PSF was increased, the post-running reduction of muscular force was lower and the recovery of muscle function was faster within days following the session. In addition, when running downhill, the PSF is reduced [25,27,28] whereas according to Snyder & Farley [28], the optimal step frequency, i.e., the step frequency at which the oxygen consumption is minimal, is not significantly modified. Therefore, one could expect that increasing PSF during downhill running will result in a running frequency closer to the optimal one, and will then be beneficial regarding both the risk of injuries and the cost of running [29]. ...
Aims
Injuries to the lumbopelvic region are often debilitating and result in significant time loss from sports participation. Different factors which have been correlated with the occurrence of injuries are, for example, the magnitude of the anterior pelvic tilt angle and the repetitive impacts the body has with the ground. When running downhill, step length is longer, which translates into a greater joint range of motion, and the vertical velocity at foot contact is greater. As a result, risks of overuse injury could be greater as compared to level running. To help prevent such injuries, we hypothesise that increasing step frequency may be a valid way to reduce the impact with the ground and the maximal anterior pelvic tilt without affecting oxygen consumption, both in level and downhill running.
Methods
We analysed 10 inexperienced runners at preferred and +10% of step frequency during level and downhill running. We recorded the oxygen uptake together with running kinematics and kinetics.
Results
When the step frequency was increased by 10%, both in downhill and level running, neither the oxygen uptake nor the running kinetics were modified. In contrast, the maximal anterior pelvic tilt was significantly reduced with increased step frequency.
Conclusion
For inexperienced runners, these findings show that increasing step frequency may partly reduce the anterior pelvic tilt without significantly influencing the running economy.
... HR, speed and SF are measured by many commercially available sports devices, which would in principle allow runners to determine their own SFopt. Reviewing results from previous studies revealed that both SFself and SL increase when individual runners increase their speed 40,42,43,45,47,[49][50][51]96,[119][120][121][122] . Therefore, it can be expected that SFopt also increases with speed (Figure 4.1c-d). ...
The large-scale usage of smartphone applications and sports watches in running provides the potential to lower injury risk and improve performance. To achieve these common goals, contextual factors need to be taken into account to provide users with accurate and personal feedback. This thesis aims to develop methods to improve the quality of wearable feedback and its interpretation.
Within the data process from parameter detection to feedback to the user, the are several ways to improve the quality of the feedback. The studies in this thesis demonstrate various possibilities. The thesis projects concern an improved algorithm for cycle detection; a method to cross-validate speed; an approach to determine an energetic optimal running technique; highlight the importance of individual differences; and a concise, yet comprehensive description of the full spectrum of running styles.
It is concluded that to further improve the quality of wearable feedback, cross-validation, self-optimization, biomechanical dependencies, and individual differences should be considered as demonstrated in the thesis.
... [9] Increasing cadence (at a constant velocity) can favorably impact numerous variables including braking impulses, foot strike location, patellofemoral pressures, center of pressure location and patellofemoral contact area [10][11][12][13]. There is also strong potential for cadence to modify caloric cost, as slower cadence increases leg muscle activation during stance [14] and swing phases of the gait cycle [15]; increasing muscle pre-activation with faster cadence may reduce the caloric cost associated with relatively larger braking impulses and greater vertical displacement of the center of mass associated with longer steps and slow cadence [11,15]. Thus, modifying cadence can potentially simultaneously improve biomechanical and energy cost responses [16,17] to long downhill runs. ...
... HR, speed and SF are measured by many commercially available sports devices, which would in principle allow runners to determine their own SF opt . Reviewing results from previous studies revealed that both SF self and SL increase when individual runners increase their speed [1,4,9,14,19,21,22,[28][29][30][31][32][33]. Therefore, it can be expected that SF opt also increases with speed (Fig 1c and 1d). ...
During running at a constant speed, the optimal stride frequency (SF) can be derived from the u-shaped relationship between SF and heart rate (HR). Changing SF towards the optimum of this relationship is beneficial for energy expenditure and may positively change biomechanics of running. In the current study, the effects of speed on the optimal SF and the nature of the u-shaped relation were empirically tested using Generalized Estimating Equations. To this end, HR was recorded from twelve healthy (4 males, 8 females) inexperienced runners, who completed runs at three speeds. The three speeds were 90%, 100% and 110% of self-selected speed. A self-selected SF (SFself) was determined for each of the speeds prior to the speed series. The speed series started with a free-chosen SF condition, followed by five imposed SF conditions (SFself, 70, 80, 90, 100 strides·min⁻¹) assigned in random order. The conditions lasted 3 minutes with 2.5 minutes of walking in between. SFself increased significantly (p<0.05) with speed with averages of 77, 79, 80 strides·min⁻¹ at 2.4, 2.6, 2.9 m·s⁻¹, respectively). As expected, the relation between SF and HR could be described by a parabolic curve for all speeds. Speed did not significantly affect the curvature, nor did it affect optimal SF. We conclude that over the speed range tested, inexperienced runners may not need to adapt their SF to running speed. However, since SFself were lower than the SFopt of 83 strides·min⁻¹, the runners could reduce HR by increasing their SFself.
... They reported no differences in leg shock, haemolysis, and muscle damage between the three midsole conditions. Conversely, Rowlands et al. (2001) showed that 45 min of intermittent downhill running (9 × 5 min) at 10.5 km h −1 and −14.9 % grade was less harmful when increasing stride frequency (i.e., 108 % of the preferred stride frequency), despite the greater muscle activity found during downhill running with a greater frequency (Sheehan and Gottschall 2013). The reasons for this phenomenon may be that eccentrically based exercises performed at shorter muscle lengths (as observed in downhill running at a higher stride frequency) induce lower muscle damage than that performed at longer muscle lengths (as observed in downhill running at a lower stride frequency) (Child et al. 1998;Jones et al. 1989;Butterfield and Herzog 2006). ...
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 neuro-physiological 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 have several fatigue-related intrinsic features compared to level running. Downhill running induces severe lower limb tissue damage, indirectly evidenced by massive increases in plasma creatine kinase/myoglobin concentration or inflammatory markers. Also 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, and the difference of energy cost versus heat storage or muscle activity changes in downhill, level and uphill running are also discussed.
... During hiking, pain and injuries are reported, especially during the downhill phase, 1 and moreover the risk of falling and slipping is higher for downhill walking than for uphill or level walking. 2,3 During downhill walking eccentric muscle contraction is needed to reduce the gain in kinetic energy due to descending during walking. 4 In other words, during downhill walking higher loads occur at the knee because there is the tendency to use eccentric force with short-muscle lengthening to control the downhill kinetic force. ...
Context:
During sport activity knee proprioception might worsen. This decrease in proprioceptive acuity negatively influences motor control and therefore may increase injury risk. Hiking is a common activity characterized by a higher intensity exercise phase during uphill walking and a lower intensity exercise phase during downhill walking. Pain and injuries are reported in hiking especially during the downhill phase.
Objective:
The purpose of this study was to examine the effect of a "hiking-fatigue-protocol" on joint position sense.
Design:
Repeated measures. Setting: University research laboratory.
Participants:
Twenty-four non-professional sportswomen without knee injuries took part in this study.
Main outcome measures:
Joint position sense was tested at the beginning, after 30 minutes uphill walking and after 30 minutes downhill walking on a treadmill (continuous protocol).
Results:
After downhill walking joint position sense was significantly worse than in the test at the beginning (p = 0.035, α = 0.05). After uphill walking no differences were observed in comparison with the test at the beginning (p = 0.172, α = 0.05) or in comparison with the test after downhill walking (p = 0.165, α = 0.05).
Conclusion:
Downhill walking causes impairment in knee joint position sense. Considering these results, injury prevention protocols for hiking should focus on maintaining and improving knee proprioception during the descending phase.
Importance Running-related injuries are highly prevalent.
Objective Synthesise published evidence with international expert opinion on the use of running retraining when treating lower limb injuries.
Design Mixed methods.
Methods A systematic review of clinical and biomechanical findings related to running retraining interventions were synthesised and combined with semistructured interviews with 16 international experts covering clinical reasoning related to the implementation of running retraining.
Results Limited evidence supports the effectiveness of transition from rearfoot to forefoot or midfoot strike and increase step rate or altering proximal mechanics in individuals with anterior exertional lower leg pain; and visual and verbal feedback to reduce hip adduction in females with patellofemoral pain. Despite the paucity of clinical evidence, experts recommended running retraining for: iliotibial band syndrome; plantar fasciopathy (fasciitis); Achilles, patellar, proximal hamstring and gluteal tendinopathy; calf pain; and medial tibial stress syndrome. Tailoring approaches to each injury and individual was recommended to optimise outcomes. Substantial evidence exists for the immediate biomechanical effects of running retraining interventions (46 studies), including evaluation of step rate and strike pattern manipulation, strategies to alter proximal kinematics and cues to reduce impact loading variables.
Summary and relevance Our synthesis of published evidence related to clinical outcomes and biomechanical effects with expert opinion indicates running retraining warrants consideration in the treatment of lower limb injuries in clinical practice.
At a given running speed, humans strongly prefer to use a stride frequency near their 'optimal' stride frequency that minimizes metabolic cost. Although there is no definitive explanation for why an optimal stride frequency exists, elastic energy usage has been implicated. Because the possibility for elastic energy storage and return may be impaired on slopes, we investigated whether and how the optimal stride frequency changes during uphill and downhill running. Presuming a smaller role of elastic energy, we hypothesized that altering stride frequency would change metabolic cost less during uphill and downhill running than during level running. To test this hypothesis, we collected force and metabolic data as nine male subjects ran at 2.8 m s(-1) on the level, 3 deg uphill and 3 deg downhill. Stride frequency was systematically varied above and below preferred stride frequency (PSF ±8% and ±15%). Ground reaction force data were used to calculate potential, kinetic and total mechanical energy, and to calculate the theoretical maximum possible and estimated actual elastic energy storage and return. Contrary to our hypothesis, we found that neither the overall relationship between metabolic cost and stride frequency nor the energetically optimal stride frequency changed substantially with slope. However, estimated actual elastic energy storage as a percentage of total positive power increased with increasing stride frequency on all slopes, indicating that muscle power decreases with increasing stride frequency. Combined with the increased cost of force production and internal work with increasing stride frequency, this leads to an intermediate optimal stride frequency and overall U-shaped curve.
An eccentric muscle activation is the controlled lengthening of the muscle under tension. Functionally, most leg muscles work eccentrically for some part of a normal gait cycle, to support the weight of the body against gravity and to absorb shock. During downhill running the role of eccentric work of the 'anti-gravity' muscles--knee extensors, muscles of the anterior and posterior tibial compartments and hip extensors--is accentuated. The purpose of this paper is to review the relationship between eccentric muscle activation and muscle damage, particularly as it relates to running, and specifically, downhill running.
The metabolic cost and the mechanical work of running at different speeds and gradients were measured on five human subjects. The mechanical work was partitioned into the internal work (Wint) due to the speed changes of body segments with respect to the body centre of mass and the external work (Wext) due to the position and speed changes of the body centre of mass in the environment. Wext was further divided into a positive part (W+ext) and a negative part (W-ext), associated with the energy increases and decreases, respectively, over the stride period. For all constant speeds, the most economical gradient was -10.6 +/-0.5% (S.D., N = 5) with a metabolic cost of 146.8 +/- 3.8 ml O2 kg-1 km-1. At each gradient, there was a unique W+ext/W-ext ratio (which was 1 in level running), irrespective of speed, with a tendency for W-ext and W+ext to disappear above a gradient of +30% and below a gradient of -30%, respectively. Wint was constant within each speed from a gradient of -15% to level running. This was the result of a nearly constant stride frequency at all negative gradients. The constancy of Wint within this gradient range implies that Wint has no role in determining the optimum gradient. The metabolic cost C was predicted from the mechanical experimental data according to the following equation: [formula: see text] where eff- (0.80), eff+ (0.18) and effi (0.30) are the efficiencies of W-ext, W+ext and Wint, respectively, and el- and el+ represent the amounts of stored and released elastic energy, which are assumed to be 55J step-1. The predicted C versus gradient curve coincides with the curve obtained from metabolic measurements. We conclude that W+ext/W-ext partitioning and the eff+/eff- ratio, i.e. the different efficiency of the muscles during acceleration and braking, explain the metabolic optimum gradient for running of about -10%.
At running speeds less than about 13 km h-1 the freely chosen step frequency (ffree) is lower than the frequency at which the mechanical power is minimized (fmin). This dissociation between ffree and fmin was investigated by measuring mechanical power, metabolic energy expenditure and apparent natural frequency of the body's bouncing system (fsist) during running at three given speeds with different step frequencies. The ffree requires a mechanical power greater than that at fmin mainly due to a larger vertical oscillation of the body at each step. Energy expenditure is minimal and the mechanical efficiency is maximal at ffree. At a given speed, an increase in step frequency above ffree results in an increase in energy expenditure despite a decrease in mechanical power. On the other hand, a decrease in step frequency below ffree results in a larger increase in energy expenditure associated with an increase in mechanical power. When the step frequency is forced to values above or below ffree, fsist is forced to change similarly by adjusting the stiffness of the bouncing system. However the best match between fsist and step frequency takes place only in proximity of ffree (2. 6-2.8 Hz). It is concluded that during running at speeds less than 13 km h-1 energy is saved by tuning step frequency to fsist, even if this requires a mechanical power larger than necessary.
We hypothesized that the elevated primary O(2) uptake (VO(2)) amplitude during the second of two bouts of heavy cycle exercise would be accompanied by an increase in the integrated electromyogram (iEMG) measured from three leg muscles (gluteus maximus, vastus lateralis, and vastus medialis). Eight healthy men performed two 6-min bouts of heavy leg cycling (at 70% of the difference between the lactate threshold and peak VO(2)) separated by 12 min of recovery. The iEMG was measured throughout each exercise bout. The amplitude of the primary VO(2) response was increased after prior heavy leg exercise (from mean +/- SE 2.11 +/- 0.12 to 2.44 +/- 0.10 l/min, P < 0.05) with no change in the time constant of the primary response (from 21.7 +/- 2.3 to 25.2 +/- 3.3 s), and the amplitude of the VO(2) slow component was reduced (from 0.79 +/- 0.08 to 0.40 +/- 0.08 l/min, P < 0.05). The elevated primary VO(2) amplitude after leg cycling was accompanied by a 19% increase in the averaged iEMG of the three muscles in the first 2 min of exercise (491 +/- 108 vs. 604 +/- 151% increase above baseline values, P < 0.05), whereas mean power frequency was unchanged (80.1 +/- 0.9 vs. 80.6 +/- 1.0 Hz). The results of the present study indicate that the increased primary VO(2) amplitude observed during the second of two bouts of heavy exercise is related to a greater recruitment of motor units at the onset of exercise.
Explaining the energetics of walking and running has been difficult because the distribution of energy use among individual
muscles has not been known. We estimated energy use by measuring blood flow to the hindlimb muscles in guinea fowl. Blood
flow to skeletal muscles is controlled locally and varies directly with metabolic rate. We estimate that the swing-phase muscles
consume 26% of the energy used by the limbs and the stance-phase muscles consume the remaining 74%, independent of speed.
Thus, contrary to some previous suggestions, swinging the limbs requires an appreciable fraction of the energy used during
terrestrial legged locomotion. Models integrating the energetics and mechanics of running will benefit from more detailed
information on the distribution of energy use by the muscles.
The metabolic cost of leg swing in running is highly controversial. We investigated the cost of initiating and propagating leg swing at a moderate running speed and some of the muscular actions involved. We constructed an external swing assist (ESA) device that applied small anterior pulling forces to each foot during the first part of the swing phase. Subjects ran on a treadmill at 3.0 m/s normally and with ESA forces up to 4% body weight. With the greatest ESA force, net metabolic rate was 20.5% less than during normal running. Thus we infer that the metabolic cost of initiating and propagating leg swing comprises approximately 20% of the net cost of normal running. Even with the greatest ESA, mean electromyograph (mEMG) of the medial gastrocnemius and soleus muscles during later portions of stance phase did not change significantly compared with normal running, indicating that these muscles are not responsible for the initiation of leg swing. However, with ESA, rectus femoris mEMG during the early portions of swing phase was as much as 74% less than during normal running, confirming that it is responsible for the propagation of leg swing.
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< 0.05); EMG of BF was greater during UR than during DR (p< 0.05); EMG of GAS differed significantly in the order: UR>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, possibly due to its undergoing eccentric movement.
The purpose of this study was to determine if rate of oxygen consumption (VO 2) during running is influenced by an interaction of stride frequency (SF) and running speed. Ten well-trained runners (66.3±8.8 kg; 23±5 yrs; 1.75±0.1 m) completed 3 15-minute runs. During each 15-minute run, subjects ran for 5 minutes at speeds of 3.13, 3.58, and 4.02 m/s. During the first 15-minute run, subjects were allowed to freely select a preferred stride frequency (PSF). The remaining two 15-minute runs consisted of running using SF that were ±15% of PSF at each speed. Using a repeated measures ANOVA, it was determined that VO 2 was different across speeds (p<0.05) and tended to be different between SF (p=0.059) with no interaction between speed and SF observed (p>0.05). VO 2 was less during running at PSF than when using the 15% lower SF at 3.13 m/s and 3.58 m/s (p<0.05). VO 2 was not different between other SF comparisons. PSF did change across speeds, but the change was subtle (about 4% per m/s increase in speed). It seems that there is an optimal SF range across speeds vs. a unique optimal SF at each speed that is important to maintain during distance running.
SUMMARY The energetic cost of generating muscular force was studied by measuring the energetic cost of carrying loads in rats, dogs, humans, and horses for loads ranging between 7 and 27% of body mass. Oxygen consumption increased in direct proportion to mass supported by the muscles, i.e. %jJ?°i= I-OI±S.D. ± 0-017, mL/m where VOi< L is the oxygen consumption of the animal running with a load, T^, is the oxygen consumption at the same speed without a load, mL is the mass of the animal plus the load, and m is the mass of the animal. Stride frequency, average number of feet on the ground over an integral number of strides, the time of contact of each foot relative to the other feet, and the average vertical acceleration during the contact phase were not measurably changed by the loads used in our experiments. From these obser- vations we conclude that the average accelerations of the centre of mass of the animal are not changed by carrying the loads, and that muscular force deve- loped by the animal increases in direct proportion to the load. It follows that the rate of energy utilization by muscles of an animal as it runs along the ground at any particular speed is nearly directly proportional to the force exerted by its muscles. The energetic cost of generating force over an interval of time (J Fdt) increases markedly with running speed. An important consequence of the direct proportionality between in- creased oxygen consumption and mass of the load is that small animals expend much more energy to generate a given force at a given speed than large animals.
The energy output is investigated during running at constant speed with varying length of stride and stride frequency.
The results show that the most economical stride length always lies in the region of the freely chosen one when the subject is well-trained. An increase of stride length above the freely chosen one gives a larger increase of O2-consumption than a corresponding shortening of the stride. There is for every runner and every speed an optimum of stride length and frequency.
The purpose of this paper is to address four aspects of surface electromyography associated with crosstalk between adjacent recording sites. The first issue that is addressed in the potential crosstalk between electrodes located on muscles with different functions: antagonist pairs, or muscles with one common and one different function (i.e. soleus/peroneus longus or soleus/ gastrocnemius). Practical functional tests are utilized to demonstrate the crosstalk between muscle pairs to be negligible. The second goal is to estimate the depth of pick-up and the crosstalk between myoelectric signals from agonist muscles using a theoretical model. The depth of pick-up was estimated to be 1.8 cm (including a 2 mm layer of skin and fat) using electrodes of 49 mm(2) with bipolar spacing of 2.0 cm. A cross-correlation technique is demonstrated which predicts the common signal (crosstalk) between surface electrodes with electrode-pair spacing of 1 cm around a hypothetical muscle. The predicted crosstalk using cross-correlation measures was 49% at 1 cm electrode-pair spacing dropping to 13% at 2 cm spacing and 4% at 3 cm. The third part compares these predictions with crosstalk measures from experimental recordings taken from electrode pairs spaced 2.5 cm apart around the quadriceps. At 2.5 cm spacing there was 22-24% common signal dropping to between 4-7% at 5 cm and to between 1 and 2% at 7.5 cm. The fourth and last component of this report assesses three methods to decrease the range of pick-up and thereby potential crosstalk: electrodes of smaller surface area, reduced bipolar spacing and mathematical differentiation. All three techniques reduce the common signal by varying amounts; all three techniques combined reduce the predicted crosstalk for the 1.0 cm electrode-pair spacing from 49-10.5%.
1. At high running speeds, the step frequency becomes lower than the apparent natural frequency of the body's bouncing system. This is due to a relative increase of the vertical component of the muscular push and requires a greater power to maintain the motion of the centre of gravity, Wext. However, the reduction of the step frequency leads to a decrease of the power to accelerate the limbs relatively to the centre of gravity, Wint, and, possibly, of the total power Wtot = Wext + Wint. 2. In this study we measured Wext using a force platform, Wint by motion picture analysis, and calculated Wtot during human running at six given speeds (from 5 to 21 km h-1) maintained with different step frequencies dictated by a metronome. The power was calculated by dividing the positive work done at each step by the duration of the step (step-average power) and by the duration of the positive work phase (push-average power). 3. Also in running, as in walking, a change of the step frequency at a given speed has opposite effects on Wext, which decreases with increasing step frequency, and Wint, which increases with frequency; in addition, a step frequency exists at which Wtot reaches a minimum. However, the frequency for a minimum of Wtot decreases with speed in running, whereas it increases with speed in walking. This is true for both the step-average and the push-average powers. 4. The frequency minimizing the step-average power equals the freely chosen step frequency at about 13 km h-1: it is higher at lower speeds and lower at higher speeds. The frequency minimizing the push-average power approaches the freely chosen step frequency at high speeds (around 22 km h-1 for our subjects). 5. It is concluded that the increase of the vertical push does reduce the step-average power, but that a limit is set by the increase of the push-average power. Between 13 and 22 km h-1 the freely chosen step frequency is intermediate between a frequency minimizing the step-average power, eventually limited by the maximum oxygen intake (aerobic power), and a frequency minimizing the push-average power, set free by the muscle immediately during contraction (anaerobic power). The first need prevails at the lower speed, the second at the higher speed.
1. During each step of running, trotting or hopping part of the gravitational and kinetic energy of the body is absorbed and successively restored by the muscles as in an elastic rebound. In this study we analysed the vertical motion of the centre of gravity of the body during this rebound and defined the relationship between the apparent natural frequency of the bouncing system and the step frequency at the different speeds. 2. The step period and the vertical oscillation of the centre of gravity during the step were divided into two parts: a part taking place when the vertical force exerted on the ground is greater than body weight (lower part of the oscillation) and a part taking place when this force is smaller than body weight (upper part of the oscillation). This analysis was made on running humans and birds; trotting dogs, monkeys and rams; and hopping kangaroos and springhares. 3. During trotting and low-speed running the rebound is symmetric, i.e. the duration and the amplitude of the lower part of the vertical oscillation of the centre of gravity are about equal to those of the upper part. In this case, the step frequency equals the frequency of the bouncing system. 4. At high speeds of running and in hopping the rebound is asymmetric, i.e. the duration and the amplitude of the upper part of the oscillation are greater than those of the lower part, and the step frequency is lower than the frequency of the system. 5. The asymmetry is due to a relative increase in the vertical push. At a given speed, the asymmetric bounce requires a greater power to maintain the motion of the centre of gravity of the body, Wext, than the symmetric bounce. A reduction of the push would decrease Wext but the resulting greater step frequency would increase the power required to accelerate the limbs relative to the centre of gravity, Wint. It is concluded that the asymmetric rebound is adopted in order to minimize the total power, Wext + Wint.
This paper reviews specific examples of how energy expenditure during submaximal exercise is affected by mechanical and muscular factors. Structural biomechanical variables are discussed as a possible reason for economy differences between individuals. The practical question, "Can economy of performing a certain task be modified?" is posed. Examples of how the manipulation of a particular movement pattern results in an energetic minimum (optimal phenomena) are presented. The physiological mechanisms for these phenomena are summarized. The influence of positive vs negative work and storage of elastic energy in relation to the topic of economy and muscular efficiency is considered. The effects of athletic equipment such as footwear, track surfaces, and bicycle components on economy and muscular efficiency are presented. The prospects for improving athletic performance by improving economy are evaluated, and recommendations for future directions are made.
The purpose of this study was to describe the firing pattern of 11 hip and knee muscles during running. Thirty recreational runners volunteered to run at 3 different paces with indwelling electromyographic electrodes while being filmed at 100 frames per second. Results demonstrated that medial and lateral vasti muscles acted together for knee extension during terminal swing and loading response, possibly providing a patella stabilizing role. The vastus intermedius muscle functioned with the other vasti, plus eccentrically controlled knee flexion during swing phase. The rectus femoris muscle fired with the vastus intermedius muscle and assisted the iliacus muscle with hip flexion. The hamstrings fired primarily to eccentrically control hip flexion. The adductor magnus, tensor fascia lata, and gluteus maximus muscles afforded pelvic stabilization while assisting with hip flexion and extension. Forward propulsion was provided mainly by hip flexion and knee extension, which is contrary to the view that posterior calf muscles provide propulsion during toe off. Faster running paces lead to increased activity in the muscles. This may lead to more injuries, primarily in the muscles that were contracting eccentrically.
The study was undertaken to assess the metabolic and the mechanical aspects of two different foot strike patterns in running, i.e. forefoot and rearfoot striking (FFS and RFS), and to understand whether there is some advantage for a runner to use one or the other of the two landing styles. Eight subjects performed two series of runs (FFS and RFS) on a treadmill at an average speed of 2.50, 2.78, 3.06, 3.33, 3.61, 3.89, 4.17 m s-1. Step frequency, oxygen uptake, mechanical work, and its two components, external and internal, were measured. No differences were found for step frequency, mechanical internal work per unit time and oxygen uptake, while external and total mechanical work per unit time were significantly higher, 7-12%, for FFS. The higher external work was the result of an increase of the work performed against both gravitational and inertial forces. As the energy expenditure was the same it has been speculated that a higher storage and release of energy takes place in the elastic structures of the lower leg with FFS. In a different series of experiments on six subjects contact time, time of deceleration and time of acceleration were measured by means of a video camera while running on the treadmill at 2.50, 3.33 and 4.17 m s-1, both FFS and RFS. Time of deceleration is similar for FFS and RFS, but contact time and time of acceleration are shorter, respectively 12 and 25%, for FFS.(ABSTRACT TRUNCATED AT 250 WORDS)
When humans and other mammals run, the body's complex system of muscle, tendon and ligament springs behaves like a single linear spring ('leg spring'). A simple spring-mass model, consisting of a single linear leg spring and a mass equivalent to the animal's mass, has been shown to describe the mechanics of running remarkably well. Force platform measurements from running animals, including humans, have shown that the stiffness of the leg spring remains nearly the same at all speeds and that the spring-mass system is adjusted for higher speeds by increasing the angle swept by the leg spring. The goal of the present study is to determine the relative importance of changes to the leg spring stiffness and the angle swept by the leg spring when humans alter their stride frequency at a given running speed. Human subjects ran on treadmill-mounted force platform at 2.5ms-1 while using a range of stride frequencies from 26% below to 36% above the preferred stride frequency. Force platform measurements revealed that the stiffness of the leg spring increased by 2.3-fold from 7.0 to 16.3 kNm-1 between the lowest and highest stride frequencies. The angle swept by the leg spring decreased at higher stride frequencies, partially offsetting the effect of the increased leg spring stiffness on the mechanical behavior of the spring-mass system. We conclude that the most important adjustment to the body's spring system to accommodate higher stride frequencies is that leg spring becomes stiffer.
Similarly sized bipeds and quadrupeds use nearly the same amount of metabolic energy to run, despite dramatic differences in morphology and running mechanics. It has been shown that the rate of metabolic energy use in quadrupedal runners and bipedal hoppers can be predicted from just body weight and the time available to generate force as indicated by the duration of foot-ground contact. We tested whether this link between running mechanics and energetics also applies to running bipeds. We measured rates of energy consumption and times of foot contact for humans (mean body mass 78.88 kg) and five species of birds (mean body mass range 0.13-40.1 kg). We find that most (70-90%) of the increase in metabolic rate with speed in running bipeds can be explained by changes in the time available to generate force. The rate of force generation also explains differences in metabolic rate over the size range of birds measured. However, for a given rate of force generation, birds use on average 1.7 times more metabolic energy than quadrupeds. The rate of energy consumption for a given rate of force generation for humans is intermediate between that of birds and quadrupeds. These results support the idea that the cost of muscular force production determines the energy cost of running and suggest that bipedal runners use more energy for a given rate of force production because they require a greater volume of muscle to support their body weight.
Indirect calorimetric measurements were made on two athletes running at different speeds up to 22 km/hr at grades from -20 to +15%; the function was found to be linearly related to speed. Within these limits, the net kilocalories per kilogram per kilometer values seem to be independent of speed and related only to the incline. These values are about 5–7% lower than those found in nonathletic subjects, which shows that training in atheletes does not lead to great improvement. A nomogram is given for easily calculating the energy expenditure in running when the speed and the incline are known. The energy cost per kilometer in horizontal run (1 kcal/kg) is about double that for walking at the most economical speed (4 km/ hr).
Submitted on July 31, 1962
We investigated the normal and parallel ground reaction forces during downhill and uphill running. Our rationale was that these force data would aid in the understanding of hill running injuries and energetics. Based on a simple spring-mass model, we hypothesized that the normal force peaks, both impact and active, would increase during downhill running and decrease during uphill running. We anticipated that the parallel braking force peaks would increase during downhill running and the parallel propulsive force peaks would increase during uphill running. But, we could not predict the magnitude of these changes. Five male and five female subjects ran at 3m/s on a force treadmill mounted on the level and on 3 degrees, 6 degrees, and 9 degrees wedges. During downhill running, normal impact force peaks and parallel braking force peaks were larger compared to the level. At -9 degrees, the normal impact force peaks increased by 54%, and the parallel braking force peaks increased by 73%. During uphill running, normal impact force peaks were smaller and parallel propulsive force peaks were larger compared to the level. At +9 degrees, normal impact force peaks were absent, and parallel propulsive peaks increased by 75%. Neither downhill nor uphill running affected normal active force peaks. Combined with previous biomechanics studies, our normal impact force data suggest that downhill running substantially increases the probability of overuse running injury. Our parallel force data provide insight into past energetic studies, which show that the metabolic cost increases during downhill running at steep angles.
Many studies have demonstrated that contact time is a key factor affecting both the energetics and mechanics of running. The purpose of the present study was to further explore the relationships between contact time (t(c)), step frequency (f) and leg stiffness (k(leg)) in human running. Since f is a compound parameter, depending on both contact and aerial time, the specific goal of this study was to independently vary f and t(c) and to investigate their respective effects on spring-mass characteristics during running, seeking to determine if the changes in k(leg) observed when running at different f are mainly due to inherent changes in t(c). We compared three types of constant 3.33 m s(-1) running conditions in 10 male subjects: normal running at the subject's freely chosen f, running with decreased and increased f, and decreased and increased t(c) at the imposed freely chosen f. The data from the varied f trials showed that the variation of t(c) was strongly correlated to that of k(leg) (r(2)=0.90), and the variation of f was also significantly correlated to that of k(leg) (r(2)=0.47). Further, changes in t(c) obtained in various t(c) conditions were significantly correlated to changes in k(leg) (r(2)=0.96). These results confirm that leg stiffness was significantly influenced by step frequency variations during constant speed running, as earlier demonstrated, but our more novel finding is that compared to step frequency, the effect of contact time variations appears to be a stronger and more direct determinant of k(leg). Indeed, 90-96% of the variance in k(leg) can be explained by contact time, whether this latter parameter is directly controlled, or indirectly controlled through its close relationship with step frequency. In conclusion, from the comparison of two experimental procedures, i.e. imposing various step frequency conditions vs. asking subjects to intentionally vary contact time at their freely chosen step frequency, it appears that changes in leg stiffness are mainly related to changes in contact time, rather than to those in step frequency. Step frequency appears to be an indirect factor influencing leg stiffness, through its effect on contact time, which could be considered a major determinant of this spring-mass characteristic of human running.
The determination of gait events such as heel strike and toe-off provide the basis for defining stance and swing phases of gait cycles. Two algorithms for determining event times for treadmill and overground walking based solely on kinematic data are presented. Kinematic data from treadmill walking trials lasting 20-45s were collected from three subject populations (healthy young, n=7; multiple sclerosis, n=7; stroke, n=4). Overground walking trials consisted of approximately eight successful passes over two force plates for a healthy subject population (n=5). Time of heel strike and toe-off were determined using the two new computational techniques and compared to events detected using vertical ground reaction force (GRF) as a gold standard. The two algorithms determined 94% of the treadmill events from healthy subjects within one frame (0.0167s) of the GRF events. In the impaired populations, 89% of treadmill events were within two frames (0.0334s) of the GRF events. For overground trials, 98% of events were within two frames. Automatic event detection from the two kinematic-based algorithms will aid researchers by accurately determining gait events during the analysis of treadmill and overground walking.
Atlas for electrode placement Introduction to Surface Electromyography, Gaithersberg, Maryland, MD: ASPEN; 1998 Eccentric activation and muscle damage: biomechanical and physiological considerations during downhill running
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Biomechanics of Distance Running. Champaign, IL: Human Kinetics Books; 1990. Cavanagh PR, Kram R. Mechanical and muscular factors affecting the efficiency of human movement
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Cavanagh PR. Biomechanics of Distance Running. Champaign, IL: Human Kinetics Books; 1990. Cavanagh PR, Kram R. Mechanical and muscular factors affecting the efficiency of human movement. Med Sci Sports Exerc 1985;17(3):326–31.
Two simple methods for determining gait events
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- Higginson
Zeni JA, Richards J, Higginson J. Two simple methods for determining gait events