IntrattenereLower-Limb Muscular Strategies for Increasing Running Speed

Lower-Limb Muscular Strategies for Increasing Running Speed

-

Running is a fundamental skill and a critical requirement for almost all sporting activities. Understanding the biomechanical function of the lower-limb muscle groups during running is important for improving current knowledge regarding human high happening, as well as for identifying potential factors that might be related to injury. Humans have the capacity to run at a broad spectrum of speeds. Depending acceso the particular protocol used to identify the preferred transition speed, locomotion has been found to switch from walking to running between speeds ranging from 2.0 to 2.7 m/s.29,61,77 Elite athletes have the ability to achieve maximal running speeds greater than 10 m/s (ora 36 km/h).17 The purpose of this clinical commentary is to augment the way the lower-limb muscles function to increase running speed from slow to sprinting.

We will present a brief synopsis of our main research findings to date, together with additional evidence obtained from other studies. It is worth noting that many thorough and valuable literature reviews and book chapters describing lower-limb muscle function during running already exist2,19,48,52,64,68,89 and are recommended for the interested clinician who is seeking additional material. Our intention a causa di this clinical commentary is to discuss these prior publications by highlighting some recent insights.

We will also present 2 examples to illustrate how basic science knowledge of lower-limb muscle function during running can be valuable. First, from a happening perspective, we will explore the potential mechanisms behind the decline a causa di maximum running speed a causa di the aging athlete. Second, from an injury perspective, we will demonstrate how this knowledge can be helpful for designing rehabilitation programs that aim to retrain the ability to run a causa di young, previously active adults who have sustained a traumatic brain injury (TBI).

There is an important distinction a causa di the way the lower-limb muscles operate when running at a steady-state speed, compared to when accelerating, that needs to be highlighted. When running at a steady-state speed, the lower-limb muscles function like springs storing and recovering energy with each step, and thus there is risposta negativa net change a causa di the average mechanical energy of the . When accelerating, the lower-limb muscles function like motors doing positive work and generating power to increase the kinetic energy of the . 69 , 70 It should therefore be kept a causa di mind that observations generated from studies that have compared a range of incremental steady-state running speeds may not necessarily hold true for accelerated running. One would anticipate that differences a causa di the function of the lower-limb muscles compared to steady-state running are likely to be most apparent when beginning to accelerate. During the first 3 to 4 steps when maximally accelerating, the trunk is inclined forward and the foot contacts the basso ostinato behind the ‘s center of mass. 59 Thus, the biomechanical objective is to maximize the propulsive component of the basso ostinato reaction force.

An alternative approach is to evaluate accelerated running, 11 , 59 , 60 , 81 which better resembles how running speed is increased a causa di real-life sporting situations. Unfortunately, though, evaluating accelerated running over basso ostinato can be experimentally challenging, as humans require at least 40 m to reach their maximum running speed from a stationary position (eg, from the start of a 100-m race). 16 , 59 , 60 This distance is even greater for submaximal accelerations. Most studies evaluating lower-limb biomechanics during accelerated running over basso ostinato have therefore focused acceso the first few steps of the acceleration phase 8 , 15 , 33 , 41 , 50 , 51 , 53 , 54 ora a single stride cycle midway through the acceleration phase. 30 , 31 , 34 At present, the only studies that have been able to primato basso ostinato reaction force patronato for an entire acceleration phase continuously (ie, within a single trial) have involved a specialized instrumented torque treadmill. 57 , 58

To evaluate the biomechanical function of the lower-limb muscles during running, a variety of analytical approaches can be taken. For example, many studies have used an inverse dynamics-based analysis to quantify lower-limb net joint moments across a range of running speeds. 1 , 4 , 7 , 42 , 64 , 75 , 79 The net joint moment represents the sum of the moments produced by all of the muscle-tendon units, ligaments, and contact forces spanning that joint. As the moments attributable to ligaments and contact forces are likely to be small for the primary sagittal plane joint motions during running, the net joint moment is a bulk representation of the moments produced by the muscle-tendon units spanning a joint. 19 , 90 Another analytical approach involves recording the electromyographic signal from muscles of interest, 7 , 42 – 45 , 49 , 63 , 79 which is sometimes performed a causa di conjunction with an inverse dynamics-based analysis. 7 , 42 , 79 More recently, computational musculoskeletal models have been used to investigate how lower-limb muscles function during running. 6 , 18 , 25 , 55 , 73 The advantage of this latter approach is the ability to calculate certain variables that cannot be directly measured inizio noninvasive experiments, such as relative contributions from the lower-limb muscles to the generation of the basso ostinato reaction force (ora the acceleration of the ‘s center of mass) during running. Our investigations to date have involved the simultaneous recording of trunk and lower-limb kinematics, basso ostinato reaction force, and (a causa di most instances) lower-limb muscle electromyographic signal during overground running, using able-bodied adult athletic participants 18 , 46 , 67 , 75 as well as participants who have sustained a TBI. 85 , 86 To evaluate lower-limb muscular strategies during running a causa di these 2 cohorts, we have used a combination of the aforementioned analytical approaches.

Lower-Limb Muscular Strategies for Increasing Running Speed

Running speed can be increased by pushing acceso the basso ostinato more forcefully (strategy 1), pushing acceso the basso ostinato more frequently (strategy 2), ora combining these 2 strategies. When running speed is initially increased, strategy 1 appears to be the priority. A more forceful basso ostinato contact results a causa di a longer stride length because the spends more time a causa di the air,18 and this response is exactly what we have observed to occur. When running speed changed from (2.06 ± 0.12 m/s) to slow-pace running (3.48 ± 0.06 m/s), stride length increased by 63% (from 1.62 ± 0.09 m to 2.65 ± 0.08 m), whereas stride frequency increased by only 4% (FIGURE 1).18 The lower-limb muscles largely responsible for pushing acceso the basso ostinato forcefully during running are the major ankle plantar flexors (soleus and gastrocnemius muscles).18,25

Download Figure

Download PowerPoint

FIGURE 1.

Effect of running speed acceso (A) stride length and (B) stride frequency. Experimental patronato were obtained from Dorn et al.18

By combining experimentally recorded motion analysis and basso ostinato reaction force patronato during running with computational musculoskeletal modeling, it is possible to calculate the contribution of each individual muscle force to the total basso ostinato reaction force a causa di both the vertical and the anterior-to-posterior directions. The patronato clearly demonstrate that the soleus and gastrocnemius muscles combined are responsible for a large portion of the basso ostinato reaction force a causa di the vertical direction (between 49.0% and 62.3%), and nearly all of the propulsive component of the basso ostinato reaction force a causa di the anterior/posterior direction (FIGURE 2).18 This relative reliance acceso the soleus and gastrocnemius muscles to generate the necessary basso ostinato forces during and slow- to medium-pace running is certainly advantageous. The soleus and gastrocnemius muscles are attached to the calcaneus inizio a long, compliant Achilles tendon, which has the ability to store elastic strain energy during the first half of stance and then return this energy during the second half of stance, thereby reducing the amount of power that must be generated by the soleus and gastrocnemius muscle fibers to propel the a causa di the air.20,27,46,74

Download Figure

Download PowerPoint

FIGURE 2.

The contributions from the ankle plantar flexors and knee extensors to the generation of the GRF (gray shading) when running at 4 different steady-state speeds. (A) The GRF a causa di the vertical direction. (B) The GRF a causa di the anterior/posterior direction, where the anterior (propulsive) component is positive and the posterior (braking) component is negative. represent the mean values obtained from a cohort (n = 9, 3.49 ± 0.12 m/s and 5.17 ± 0.13 m/s; n = 8, 6.96 ± 0.13 m/s; and n = 7, 8.99 ± 0.67 m/s) of able-bodied adult athletic participants. Note that a causa di the anterior/posterior direction (B), the combined contribution from the soleus and gastrocnemius muscles during the middle portion of stance becomes positive before the development of the propulsive component of the GRF, because these muscles must counter the opposing effects from other lower-limb muscles (eg, the vasti and rectus femoris muscles) that are still providing a contribution to the braking component at this time. Experimental patronato were obtained from Dorn et al.18 Abbreviations: BW, weight; GRF, basso ostinato reaction force.

As running speed approaches sprinting, the ability to push acceso the basso ostinato more forcefully appears to become less effective. There are many biomechanical observations that provide evidence to this effect. First, we found the percentage increase a causa di stride length to become progressively smaller with each increment a causa di running speed, such that stride length changed very little between fast-pace running (6.97 ± 0.09 m/s) and sprinting (8.95 ± 0.70 m/s) (FIGURE 1A). This relationship between stride length and running speed has also been reported a causa di other studies.28,62,65,72 Second, a causa di a similar manner to stride length, the increase a causa di the positive work done (ora the energy generated) at the ankle joint during stance becomes progressively smaller with faster running, despite dramatic rises a causa di the magnitude of soleus activation (FIGURE 3). Third, the time a runner spends a causa di the air is determined by the effective impulse applied by the lower limb to the running surface.82,83 The effective impulse represents the ambiente underneath the vertical basso ostinato reaction force that exceeds weight (FIGURE 4). The effective impulse increases a causa di magnitude from slower to intermediate running speeds before decreasing at fast running speeds. This relationship has been reported a causa di several studies investigating running at a range of discrete steady-state speeds,65,82,83 and we also found an identical result (FIGURE 4). Fourth, when increasing running speed beyond 6.96 ± 0.13 m/s, the peak magnitude of the combined contribution from the soleus and gastrocnemius muscles to the basso ostinato reaction force can be seen to altopiano a causa di the vertical direction (FIGURE 2A), whereas a causa di the anterior/posterior direction it decreases slightly for the propulsive component (FIGURE 2B). Fifth, perhaps the most compelling evidence of all is provided by the relationship between running speed and the peak force developed a causa di the Achilles tendon. These highly unique patronato were recorded under a causa di brillante conditions by surgically inserting a buckle-type transducer around the tendon.37,38 As is evident a causa di FIGURE 5, the peak Achilles tendon force was found to be highest at running speeds of approximately 6.0 m/s and decreased a causa di magnitude thereafter. The profile of the peak Achilles tendon force plotted against running speed (FIGURE 5) has a remarkable degree of similarity to that evident for the effective impulse (FIGURE 4), substantiating our model prediction that the soleus and gastrocnemius muscles are responsible for generating a large proportion of the basso ostinato reaction force during running.

Download Figure

Download PowerPoint

FIGURE 3.

Ankle joint power and soleus EMG signal with increasing running speed for a single representative, able-bodied, adult athletic participant. (A) The temporal relationship between ankle joint power (blue line) and soleus EMG signal. for soleus EMG signal are presented at 2 stages through the signal-filtering process: first, after being high-pass filtered at 20 Hz ( wavy lines); and second, after being full-wave rectified and then low-pass filtered at 20 Hz, that is, the linear envelope (orange line). All EMG signal patronato are normalized as a fraction of the mean of the linear envelope for the maximum running-speed trial (9.72 m/s). The stance phase is indicated by the vertical gray-shaded . (B) The energy generated by the ankle joint for each running-speed condition. The energy generated (ora positive work done) represents the ambiente under the positive portion of the ankle joint power curve displayed a causa di (A). (C) The magnitude (mean of the linear envelope) of the soleus EMG signal for each running-speed condition. Ankle joint power patronato were obtained from Schache et al.75 Abbreviation: EMG, electromyographic.

Download Figure

Download PowerPoint

FIGURE 4.

Effect of running speed acceso the effective impulse (impulseeff) of the vertical GRF. The effective impulse represents the ambiente underneath the vertical GRF that exceeds BW (as indicated by small caption inside main plot). represent the mean ± SD values obtained from a cohort (n = 9, 2.02 ± 0.02 m/s, 3.38 ± 0.06 m/s, and 5.03 ± 0.10 m/s; n = 8, 6.97 ± 0.09 m/s; n = 7, 8.95 ± 0.70 m/s) of able-bodied adult athletic participants. Experimental patronato were obtained from Dorn et al.18 Abbreviations: BW, weight; GRF, basso ostinato reaction force.

Download Figure

Download PowerPoint

FIGURE 5.

Effect of running speed acceso peak Achilles tendon forces during running for a single participant. The graph displays the recorded peak force for a range of discrete steady-state running speeds using both a heel-contact technique (blue squares) and a forefoot-contact technique (orange squares). All patronato obtained from Komi37 and Komi et al.38

Why does the force-generating capacity of the ankle plantar flexors become less effective with faster running? It is clearly not to a reduction a causa di activation. Activation of the ankle plantar flexors increases dramatically as running speed approaches sprinting, as we (FIGURE 3C) and other studies43,63 have found. The less effective force-generating capacity of the soleus and gastrocnemius muscles with faster running must therefore be explained acceso the basis of an unfavorable muscle-fiber force-velocity ora force-length relationship (ora both). As running speed increases, the duration of the stance phase becomes shorter,82,83 thus greater force must be applied to the basso ostinato (strategy 1) a causa di ever-decreasing periods. From a force-velocity perspective, shorter basso ostinato contact times mean that the soleus and gastrocnemius muscles are required to contract with progressively increased shortening velocities, thereby potentially reducing the peak forces that can be generated under such conditions.18 Both experimental and modeling-based studies support this notion. For example, Weyand et al82 compared maximum sprinting with maximum one-legged forward hopping to demonstrate that if stance-phase time is allowed to increase (as is evident a causa di hopping), the lower limb does indeed have the ability to generate a much greater effective impulse than that observed during sprinting. Furthermore, Miller et al55 used elaboratore elettronico simulations to quantify the effects of muscle mechanical properties acceso maximum sprinting speed. They found the muscle fiber force-velocity relationship to be the most critical factor limiting happening. From a force-length perspective, Rubenson et al71 have shown that when running at 3.0 m/s, the soleus primarily operates near the cima, flatter portion of the ascending limb of the force-length relation (FIGURE 6). It is possible that the greater level of activation with faster running causes muscle fiber shortening, and thus the operating region acceso the force-length curve shifts to the left, the steeper portion of the ascending limb.46 While such a shift might seem counterproductive a causa di terms of the efficiency with which force is generated, it may be advantageous a causa di terms of facilitating the utilization of tendon stretch and recoil. Tendon has the capacity to recoil at a much faster velocity than muscle fibers can shorten,3,36 which could be a mechanism used by the ankle plantar flexors to help push acceso the basso ostinato as quickly as possible.

Download Figure

Download PowerPoint

FIGURE 6.

The muscle force-length relationship. The gray shading indicates the operating region for the soleus muscle when running at 3.0 m/s, as reported by Rubenson et al.71

Running speeds beyond approximately 7.0 m/s can be achieved despite little change a causa di the energy generated at the ankle joint during the second half of stance (FIGURE 3) and a reduction a causa di the effective impulse (FIGURE 4). As running speed approaches sprinting, the dominant lower-limb muscular strategy shifts toward one that is concerned with swinging the lower limbs and thereby pushing acceso the basso ostinato more frequently (strategy 2). When progressing from fast-pace running (6.97 ± 0.09 m/s) to sprinting (8.95 ± 0.70 m/s), we found stride frequency to increase by 25%, whereas stride length changed very little (FIGURE 1). Nummela et al65 also found that running speeds beyond 7 m/s were achieved by increasing stride frequency rather than stride length. Additional evidence of the shift toward strategy 2 is provided by the relationship between running speed and the amount of positive work done ora energy generated at the hip during swing (FIGURE 7). A second-order polynomial equation fitted to the patronato a causa di FIGURE 7 demonstrates that almost all of the variability a causa di the energy generated at the hip during swing could be explained by running speed ala (work = 0.052 × speed2 − 0.034 × speed + 0.180) (2 = 0.96). Greater stride frequency (strategy 2) therefore increases the biomechanical demand acceso the hip muscles dramatically. Energy is generated by the iliopsoas during the first half of swing to accelerate the hip into flexion, and then energy is generated by the gluteus maximus during the second half of swing to accelerate the hip into extension and shift the foot underneath the a causa di preparation for basso ostinato contact.18 One of the consequences of switching from strategy 1 to strategy 2 as running speed approaches sprinting is that the forces (gravity and centrifugal) acting about the hip and knee joints during terminal swing increase a causa di magnitude dramatically. Large “external” hip flexor and knee extensor torques develop at this time a causa di the stride cycle,75 which are primarily opposed by the hamstrings.12,13,76 This biomechanical function may be of clinical relevance a causa di terms of understanding the apparent injury risk for the hamstrings during high-speed running.14

Download Figure

Download PowerPoint

FIGURE 7.

Effect of running speed acceso the positive work done (ora energy generated) at the hip joint during swing. The blue squares represent individual participant patronato. A second-order polynomial equation was fitted to the patronato (black dashed line), demonstrating that almost all of the variability a causa di the energy generated at the hip during swing could be explained by running speed ala (work = 0.052 × speed2 − 0.034 × speed + 0.180) (2 = 0.96). Experimental patronato were obtained from Schache et al.75

Does Aging Affect the Ability to Increase Running Speed?

Maximum running speed is known to deteriorate with aging.24,56 For example, Hamilton24 found maximum running speed to decrease from approximately 9 m/s for runners aged 30 to 39 years to approximately 5 m/s for runners aged over 90 years. Thus, with older age, the spectrum of running speeds that can be achieved becomes progressively smaller. What is the reason for this decline a causa di happening? Does aging adversely affect the ability to push acceso the basso ostinato forcefully (strategy 1) ora more frequently (strategy 2), ora both? To answer these questions, several studies have compared stride-cycle parameters during sprinting for athletes across a broad age range.24,39,40 With aging, stride rate was found to remain relatively invariant,24,39,40 whereas stride length decreased24,39,40 and stance-phase time increased.39,40 Hence, such findings suggest that the decline a causa di maximum running speed a causa di the aging athlete is mostly related to a reduction a causa di the effectiveness of the stance limb to push acceso the basso ostinato forcefully (strategy 1). Further evidence for this premise is provided by results from studies comparing the running biomechanics of older (greater than 60 years of age) versus younger (less than 30 years of age) people at matched submaximal running speeds. Compared to their younger counterparts, older people run with shorter stride length10,22,35 and a propulsive at the ankle joint (ie, reduced energy generated ora positive work done by the ankle joint during the second half of stance).23,35 It has been proposed that the main characteristics that are likely to be responsible for the deterioration a causa di maximum running speed with aging are decreased muscle strength, slower rate of muscle force development and transmission, and reduced storage and recovery of tendon elastic strain energy.5 Given that the soleus and gastrocnemius muscles have a dominant role a causa di producing the necessary basso ostinato forces during running (FIGURE 2) and that these muscles rely heavily acceso the utilization of tendon elastic strain energy for generating power during stance,20,27,46,74 it would seem likely that the rate at which maximum running speed declines with aging is critically dependent acceso the function of the soleus and gastrocnemius muscles. Optimizing the function of the ankle plantar flexors (ie, higher force-generating capability, faster rate of force development, and increased tendon stiffness) inizio targeted resistance and explosive plyometric drills would therefore appear to be of high priority for veteran sprinting athletes endeavoring to counterbalance the effect of aging.

Acquired Impairments of Lower-Limb Muscle Function

While aging appears to impair lower-limb muscle function and lead to a decline a causa di maximum running speed, such a process occurs very slowly and only begins beyond age 30.56 Per mezzo di contrast, there are other situations a causa di which impairments of lower-limb muscle function occur suddenly and are considerably more severe. One such example is TBI. People who have sustained a TBI (eg, from a motor vehicle accident) represent an ideal model for understanding how lower-limb muscular strategies for increasing running speed are influenced by impairments of muscle function. The reason is 2-fold. First, it is adolescents and young adults who are most at risk of TBI,80 many of whom were participating a causa di running-based sports prior to their injury and therefore have the desire to return to similar activities. Second, it is quite common for people following TBI to experience persisting difficulties with high-level mobility tasks, such as running.66 Our research has involved participants who have typically sustained an extremely severe TBI. This classification is based acceso the length of posttraumatic amnesia,78 which for our cohort averaged 61.3 days.85 One of our key objectives thus far has been the identification of factors that relate to improved functional outcome, and we have found that peak power generation at the ankle during walking is a strong predictor of a better high-level mobility outcome a causa di people following TBI.88 Per mezzo di other words, people subsequent to TBI who are able to use their calf muscles to push acceso the basso ostinato adequately when walking are far more likely to be capable of recovering the ability to run.

How do people subsequent to TBI run a causa di comparison to their healthy, able-bodied counterparts? Even at relatively slow running speeds, people subsequent to TBI appear to have greater reliance acceso proximal muscle function, not just for leg swing (strategy 2) but also to aid with force generation during stance (strategy 1). Williams et al85 found that when people run subsequent to TBI, they do so with a decreased stride length and an increased stride rate, and they generate less power at the ankle acceso their more affected side, when compared to healthy adults running at the same speed. To further illustrate some of the typical disparities observed, we have compared the patronato of a single representative participant who sustained a TBI (17-year-old cattiveria, 16 months postinjury) and successfully regained the ability to run at 3.5 m/s to those of a group of able-bodied adult athletic participants (FIGURE 8). Peak power generation at the ankle for the participant with TBI was found to be 11.5 W/kg, which was approximately 25% less than that for the able-bodied adult athletic participants running at the same speed (FIGURE 8A). To determine how this participant with TBI compensated for reduced power generation at the ankle (and thus was able to run at 3.5 m/s), we calculated the percentage contributions from the hip, knee, and ankle to the average joint power generated by the lower limb during stance. Compared to the able-bodied adult athletic participants, the distribution of average joint power generation a causa di the lower limb during stance for the participant who had sustained a TBI was different: reduced power generation at the ankle was compensated for by greater power generation at the knee and the hip (FIGURE 8B). Thus, when running at 3.5 m/s, the participant who had sustained a TBI was dependent acceso using proximal muscles to generate power a causa di the lower limb, which would suggest that this participant’s capacity to run at speeds beyond 3.5 m/s was very limited.

Download Figure

Download PowerPoint

FIGURE 8.

Lower-limb joint power during running for an individual with TBI compared to a cohort (n = 7) of able-bodied adult athletic participants. All patronato were collected at a running speed of 3.5 m/s. (A) The ankle joint power during stance. Mean ± SD patronato for the able-bodied participants are indicated by the gray shading, whereas patronato for the individual with TBI are indicated by the blue line. (B) The distribution of the average joint power generated a causa di the lower limb during stance for the able-bodied participants and the individual with TBI. The average joint power generated at the hip (blue), knee (orange), and ankle () throughout stance was summed to obtain the total average joint power generated a causa di the lower limb. The average joint power generated at the hip, knee, and ankle was then expressed as a percentage of the total average joint power generated a causa di the lower limb. Experimental patronato for the able-bodied participants were obtained from Schache et al,75 whereas the experimental patronato for the individual with TBI were obtained from Williams et al.85 Abbreviation: TBI, traumatic brain injury.

While adequate calf muscle function is a critical determinant of recovering the ability to run a causa di people subsequent to TBI, the approach taken to retrain running a causa di this population focuses acceso the restoration of strategy 2 before strategy 1.87 Distal muscle function is usually more severely impaired than proximal muscle function, thus a causa di people subsequent to TBI it is easier to learn the skills to increase stride frequency (strategy 2) than those to generate greater basso ostinato forces (strategy 1). Also, the risk of falling is minimized if people subsequent to TBI are initially reintroduced to running by developing the ability to swing their lower limbs correctly before they attempt to accelerate their ‘s center of mass a causa di the forward direction. People who have sustained a TBI present with 3 common impairments of muscle function: weakness, spasticity, and poor motor control (ora quality of movement). Nevertheless, impairment-based interventions rarely translate to improvements a causa di physical function; for example, resistance a causa di people with neurological conditions increases muscle strength but does not necessarily improve locomotion happening.84 Therefore, our approach concentrates acceso the development of functional skills that simulate the biomechanical demands of running.87 While the mechanisms behind improvement a causa di running happening a causa di people who have sustained a TBI remain unclear, it is most likely attributable to neuroplasticity. The following is a brief summary of the primary exercise interventions and the milestones for progression.

The first objective is to teach the necessary skills to be able to run acceso the spot (a causa di place). This objective is achieved a causa di 3 stages. The first stage aims to restore the ability of the lower-limb muscles to decelerate and then accelerate the ‘s center of mass a causa di a vertical direction (ora support the weight of the ). This skill is initially practiced a causa di a gravity-eliminated ora gravity-reduced condition using a slide shuttle. The individual with TBI performs a slow action, pushing one limb and landing acceso the other limb, absorbing impact by landing acceso the forefoot and flexing the knee (FIGURE 9). With improvement, progression can be made to single-legged hopping (FIGURE 10). Also, the inclination of the slide shuttle can be gradually increased so that the individual with TBI begins to work against gravity more so than across gravity. Once competent a causa di the slide shuttle, the second stage involves progressing to slow acceso a mini-trampoline, finanziaria onto a rail ora pole with the upper limbs for stability before eventually performing this activity without support (FIGURE 11). The third stage involves a fast-feet running drill, where the individual with TBI practices running acceso the spot (a causa di place) acceso level basso ostinato (FIGURE 12). The focolaio is initially acceso achieving a rapid cadence with minimal knee tagliata before gradually including high knee tagliata.

Download Figure

Download PowerPoint

FIGURE 9.

Performing a slow action acceso the slide shuttle.

Download Figure

Download PowerPoint

FIGURE 10.

Performing a single-leg hop acceso the slide shuttle.

Download Figure

Download PowerPoint

FIGURE 11.

Slow acceso the mini-trampoline.

Download Figure

Download PowerPoint

FIGURE 12.

The fast-feet running drill.

The second objective is to teach the ability to safely move the ‘s center of mass a causa di the forward direction while running, initially at slow speeds but then at gradually increasing speeds as the individual becomes more skilled. For the aforementioned reasons, this objective is achieved by focusing acceso developing the skills for strategy 2 before strategy 1. Progressing a causa di this way allows the individual with TBI to better dissociate swing-phase lower-limb speed from forward speed of the . To practice strategy 2, the individual with TBI holds onto a rail ora pole with the upper limb while the weight is supported acceso the contralateral lower limb. The swing limb starts a causa di a position of 90° of hip and knee flexion and is rotated through to full hip and knee extension before returning to hip and knee flexion again, that is, simulating the lower-limb swing action a causa di running (FIGURE 13). This activity is repeated continuously and is advanced by executing the movement with greater precision and speed. The final skill that is restored is the ability of the lower-limb muscles to propel the ‘s center of mass both upward and forward (strategy 1). Bounding is introduced, initially as a single effort from one leg to the other (FIGURE 14) before performing several bounds a causa di series. Once capable of successfully bounding, the individual with TBI can then begin to practice running with increasing stride lengths. Ultimately, the ability of an individual following TBI to be able to run at faster speeds is dependent acceso how well this final skill, which is largely determined by the function of the ankle plantar flexor muscles, can be restored.

Download Figure

Download PowerPoint

FIGURE 13.

The claw exercise, used to simulate the lower-limb swing action and thereby develop the skills for pushing acceso the basso ostinato more frequently (strategy 2). The participant starts with the hip and knee joints flexed to approximately 90°. The hip and knee joints are extended simultaneously before rotating back to the start position again. The sequence of the images is from left to right.

Download Figure

Download PowerPoint

FIGURE 14.

The bounding drill aims to retrain the ability of the lower-limb muscles to propel the ‘s center of mass upward and forward, and thereby develop the skills for pushing acceso the basso ostinato more forcefully (strategy 1). The sequence of the images is from right to left.

Future Research Directions

Although some important insights regarding the lower-limb muscular strategies to increase running speed have been gleaned from the research completed to date, it is clear that many aspects are yet to be fully understood. As previously discussed, the vast majority of studies investigating the biomechanics of increasing running speed have used an experimental stile that involves a range of discrete steady-state running speeds. However, such an approach may not resemble what occurs when accelerating, especially a causa di the initial steps of the acceleration, when the trunk is inclined forward. Current knowledge regarding lower-limb muscle function during accelerated running is somewhat limited, and thus represents a valuable direction for future research. Also, another relatively new and potentially powerful way to study lower-limb muscle function during running is the use of dynamic ultrasound imaging.20,32,47 This modality can quantify a causa di brillante muscle fiber dynamics, and therefore has the potential to determine how increasing running speed influences the force-length and force-velocity relationships for certain muscles. Finally, further research is required to fully realize the biomechanical determinants of maximum running speed. Is the ability to push acceso the basso ostinato forcefully and quickly important? Evidence provided by many researchers9,65,82,83 would suggest so, a causa di which case muscular properties such as physiological cross-sectional ambiente and percentage distribution of type IIx fast-twitch fibers (especially for the major ankle plantar flexors) are likely to be key characteristics. However, the way a causa di which the lower limb pushes acceso the basso ostinato would appear to be important too, with a number of studies reporting significant correlations between maximum running speed and the magnitude of the propulsive component of the anterior/posterior basso ostinato reaction force.9,30,57,58,65 Such a relationship suggests that technique is also likely to be a critical factor a causa di determining happening. Understanding what limits maximum running speeds a causa di humans has considerable implications for designing optimal programs.

Latest news

Colazione proteica

Una colazione proteica bilanciata e gustosa: questo dovrebbe considerare il nostro capofila convito. La certezza è le quali la spuntino...

In 1980, grace jones sidestepped disco’s death-rattle into a decade obsessed with risk

Acceso July 12, 1979, hours after Minnie Riperton died con her husband’s arms at Cedars-Sinai Medical Center con Los...

Grey’s anatomy derek shepherd: 10 things you don’t know about mcdreamy

Since Grey’s Anatomy began 2005, fans have been helplessly love with derek shepherd (A.K.A. McDreamy). And to...

Brooklyn beckham and nicola peltz pose naked in a racy mirror photo

brooklyn beckham‘s fiancée Nicola Peltz mimicked his controversial neck-grabbing pose con a naked throwback selfie shared Monday.   The pair...

“searching for my father, tyrone power”: a review of romina power’s biography – park ridge classic film

“Try for beauty and truth in all you attempt.” ~ tyrone power, Sr., to his son, Tyrone Power III Searching...

Acconciature capelli ricci bimba

Andiamo alla rivelazione delle migliori acconciature capigliatura corti ovvero medi, a travisare ceffo ogni anno ! Queste misure proveniente da...

Must read

You might also likeRELATED
Recommended to you