Counterweight mass influences single-leg cycling biomechanics.

INTRODUCTION: Single-leg cycling is a commonly used intervention in exercise physiology that has applications in exercise training and rehabilitation. The addition of a counterweight to the contralateral pedal helps single-leg cycling mimic cycling patterns of double-leg cycling. To date, no research has tested (a) the influence of a wide range of counterweight masses on a person's cycling biomechanics and (b) the optimal counterweight mass to emulate double-leg cycling. OBJECTIVES: The purpose of this study was to determine the effects of varying counterweights on the kinematics (joint angles) and kinetics (joint moments, work) of cycling using a 3D analysis. METHODS: Twelve participants cycled at 50W or 100W with different counterweight masses (0 to 30 lbs, 2.5 lbs increments), while we analyzed the pedal force data, joint angles, joint moments, and joint power of the lower limb using 3D motion capture and 3D instrumented pedals to create participant-specific musculoskeletal models. RESULTS: The results showed that no single-leg cycling condition truly emulated double-leg cycling with respect to all measured variables, namely pedal forces (p ≤ 0.05), joint angles (p ≤ 0.05), joint moments(p ≤ 0.05), and joint powers (p ≤ 0.05), but higher counterweights resulted in single-leg cycling that was statistically similar (p > 0.05), but descriptively, asymptotically approached the biomechanics of double-leg cycling. CONCLUSION: We suggest that a 20-lb counterweight is a conservative estimate of the counterweight required for using single-leg cycling in exercise physiology studies, but further modifications are needed to the cycle ergometer for the biomechanics of single-leg cycling to match those of double-leg cycling.

Hip and core exercise programme prevents running-related overuse injuries in adult novice recreational runners: a three-arm randomised controlled trial (Run RCT).

OBJECTIVE: This study aims to investigate the efficacy of two exercise interventions in reducing lower extremity (LE) injuries in novice recreational runners. METHODS: Novice runners (245 female, 80 male) were randomised into hip and core (n=108), ankle and foot (n=111) or control (n=106) groups. Interventions were completed before running and included exercise programmes focusing on either (1) hip and core or (2) ankle and foot muscles. The control group performed static stretching exercises. All groups were supervised by a physiotherapist and performed the same running programme. Injuries and running exposure were registered using weekly questionnaires during the 24-week study. Primary outcome was running-related LE injury. RESULTS: The incidence of LE injuries was lower in the hip and core group compared with the control group (HR 0.66; 95% CI 0.45 to 0.97). The average weekly prevalence of overuse injuries was 39% lower (prevalence rate ratio, PRR 0.61, 95% CI 0.39 to 0.96), and the prevalence of substantial overuse injuries was 52% lower (PRR 0.48, 95% CI 0.27 to 0.90) in the hip and core group compared with the control group. No significant difference was observed between the ankle and foot group and control group in the prevalence of overuse injuries. A higher incidence of acute injuries was observed in the ankle and foot group compared with the control group (HR 3.60, 95% CI 1.20 to 10.86). CONCLUSION: A physiotherapist-guided hip and core-focused exercise programme was effective in preventing LE injuries in novice recreational runners. The ankle and foot programme did not reduce LE injuries and did not protect against acute LE injuries when compared with static stretching.

Comparison of muscle activity of the lower limbs while running on different treadmill models.

Treadmill running is a common method of exercise and to study human locomotion. Research has examined the kinematics and kinetics of overground and treadmill running, but there has been less focus on the levels of muscle activity during treadmill running. We investigated if muscle activity is different while running overground compared to running on a variety of treadmills. A total of 11 healthy individuals ran at 3 speeds (2.6, 3.6, 4.5 m/s) under 4 different running conditions (3 treadmills, overground). The three treadmills included a typical home exercise treadmill, a midsize commercial research treadmill, and a large, instrumented research treadmill. Surface EMG of the tibialis anterior (TA), gastrocnemius medialis (GM), rectus femoris (RF) and biceps femoris (BF) muscles were measured for each running condition. The integrated EMG was computed for each running condition for the stance and swing phase, as well as 100 ms before and after the heel-strike. Friedman analysis revealed significant effects during the stance phase for GM and RF at all speeds, such that muscle activation was lower on the treadmills relative to overground. During the stance phase at faster speeds, the muscle activity was higher for the TA and lower for the BF while running on the different treadmills compared to overground running. Before heel-strike, the TA was significantly less active during treadmill compared to overground running at 2.6 m/s and the RF showed significantly higher activity at 3.6 m/s and 4.5 m/s while running on the different treadmills. Summarizing, differences were mainly observed between the different treadmill conditions relative to overground running. Muscle activation differences between the different treadmill conditions were observed at faster running speeds for RF during the pre-heel-strike phase only. Different types of treadmills with different mechanical properties affects the muscle activity during stance phase as well as in preparation to heel-strike. Additionally, the muscle activity is greater during overground compared to treadmill running during the stance phase for the GM, BF, and RF.

Greater foot and footwear mechanical work associated with less ankle joint work during running.

Footwear energy storage and return is often suggested as one explanation for metabolic energy savings when running in Advanced Athletic Footwear. However, there is no common understanding of how footwear energy storage and return facilitates changes in muscle and joint kinetics. The purpose of this study was to evaluate the magnitude and timing of foot, footwear and lower limb joint powers and work while running in Advanced and Traditional Athletic Footwear. Fifteen runners participated in an overground motion analysis study. Since footwear kinetics are methodologically challenging to quantify, we leveraged distal rearfoot power analyses ('foot + footwear' power) and evaluated changes in the magnitude and timing of foot + footwear power and lower limb joint powers. Running in Advanced Footwear resulted in greater foot + footwear work, compared to Traditional Shoes, and lower positive ankle work, potentially reducing the muscular demand on the runner. The timing of foot + footwear power varied only slightly across footwear. There are exciting innovation opportunities to manipulate the timing of footwear energy and return. This study demonstrates the research value of quantifying time-series foot + footwear power, and points industry developers towards footwear innovation opportunities.

Identification of subject-specific responses to footwear during running.

Placing a stronger focus on subject-specific responses to footwear may lead to a better functional understanding of footwear's effect on running and its influence on comfort perception, performance, and pathogenesis of injuries. We investigated subject-specific responses to different footwear conditions within ground reaction force (GRF) data during running using a machine learning-based approach. We conducted our investigation in three steps, guided by the following hypotheses: (I) For each subject x footwear combination, unique GRF patterns can be identified. (II) For each subject, unique GRF characteristics can be identified across footwear conditions. (III) For each footwear condition, unique GRF characteristics can be identified across subjects. Thirty male subjects ran ten times at their preferred (self-selected) speed on a level and approximately 15 m long runway in four footwear conditions (barefoot and three standardised running shoes). We recorded three-dimensional GRFs for one right-foot stance phase per running trial and classified the GRFs using support vector machines. The highest median prediction accuracy of 96.2% was found for the subject x footwear classification (hypothesis I). Across footwear conditions, subjects could be discriminated with a median prediction accuracy of 80.0%. Across subjects, footwear conditions could be discriminated with a median prediction accuracy of 87.8%. Our results suggest that, during running, responses to footwear are unique to each subject and footwear design. As a result, considering subject-specific responses can contribute to a more differentiated functional understanding of footwear effects. Incorporating holistic analyses of biomechanical data is auspicious for the evaluation of (subject-specific) footwear effects, as unique interactions between subjects and footwear manifest in versatile ways. The applied machine learning methods have demonstrated their great potential to fathom subject-specific responses when evaluating and recommending footwear.

A foot and footwear mechanical power theoretical framework: Towards understanding energy storage and return in running footwear.

There is extreme interest surrounding the influence of advanced running footwear on running performance. The magnitude, timing, and location of mechanical energy storage and return in footwear may elucidate one way footwear influences running performance. However, the complexity of footwear makes it challenging to model footwear energy storage and return during running. The purpose of this study was to develop a practical framework for evaluating foot and footwear mechanical power profiles during running. First, a unified deformable power analysis (distal rearfoot power) was used to quantify mechanical power of the foot + footwear system. Then, qualitative mechanical power profiles of individual foot and footwear structure were developed using prior literature, benchtop footwear material properties, and experimental kinetics and kinematics. The result is a framework for understanding foot and footwear mechanical power during running using a two-stage analysis. First, foot + footwear power can be experimentally compared when running in various footwear constructions. Second, the developed framework can provide qualitative insights into which foot and footwear structures may contribute to differences in measured foot + footwear power. To highlight the utility of this framework, the timing, magnitude, and location of foot + footwear power is compared when running in different footwear constructions and with different running styles. The framework developed here provides a practical tool for footwear developers and researchers to gain intuition about the timing, relative magnitude, and location of energy storage and return from footwear during running. There are opportunities to expand on this framework to further connect footwear construction to running performance.

Estimating Running Ground Reaction Forces from Plantar Pressure during Graded Running.

Ground reaction forces (GRFs) describe how runners interact with their surroundings and provide the basis for computing inverse dynamics. Wearable technology can predict time-continuous GRFs during walking and running; however, the majority of GRF predictions examine level ground locomotion. The purpose of this manuscript was to predict vertical and anterior-posterior GRFs across different speeds and slopes. Eighteen recreationally active subjects ran on an instrumented treadmill while we collected GRFs and plantar pressure. Subjects ran on level ground at 2.6, 3.0, 3.4, and 3.8 m/s, six degrees inclined at 2.6, 2.8, and 3.0 m/s, and six degrees declined at 2.6, 2.8, 3.0, and 3.4 m/s. We estimated GRFs using a set of linear models and a recurrent neural network, which used speed, slope, and plantar pressure as inputs. We also tested eliminating speed and slope as inputs. The recurrent neural network outperformed the linear model across all conditions, especially with the prediction of anterior-posterior GRFs. Eliminating speed and slope as model inputs had little effect on performance. We also demonstrate that subject-specific model training can reduce errors from 8% to 3%. With such low errors, researchers can use these wearable-based GRFs to understand running performance or injuries in real-world settings.

Addition of a Cognitive Task During Walking Alters Lower Body Muscle Activity.

This study compared electromyography of five leg muscles during a single walking task (WALK) to a dual task (walking + cognitive task; COG) in 40 individuals (20 M and 20 F) using a wavelet analysis technique. It was hypothesized that muscle activation during the dual task would differ significantly from the walking task with respect to both timing (H1) and frequency (H2). The mean overall intensity for the COG trials was 4.1% lower for the tibialis anterior and 5.5% higher for the gastrocnemius medialis than in the WALK trials. The changes between the WALK and COG trials were short 50 ms bursts that occurred within 100 ms of heel strike in the tibialis anterior, and longer activation periods during the stance phase in the gastrocnemius medialis. No changes in overall intensity were observed in the peroneus longus, gastrocnemius lateralis, or soleus. Furthermore, no clear frequency bands within the signal could further characterize the overall changes in muscle activity during the COG task. This advances our understanding of how the division of attentional resources affects muscle activity in a healthy population of adults.

Changes in ankle work, foot work, and tibialis anterior activation throughout a long run.

BACKGROUND: The ankle and foot together contribute to over half of the positive and negative work performed by the lower limbs during running. Yet, little is known about how foot kinetics change throughout a run. The amount of negative foot work may decrease as tibialis anterior (TA) electromyography (EMG) changes throughout longer-duration runs. Therefore, we examined ankle and foot work as well as TA EMG changes throughout a changing-speed run. METHODS: Fourteen heel-striking subjects ran on a treadmill for 58 min. We collected ground reaction forces, motion capture, and EMG. Subjects ran at 110%, 100%, and 90% of their 10-km running speed and 2.8 m/s multiple times throughout the run. Foot work was evaluated using the distal rearfoot work, which provides a net estimate of all work contributors within the foot. RESULTS: Positive foot work increased and positive ankle work decreased throughout the run at all speeds. At the 110% 10-km running speed, negative foot work decreased and TA EMG frequency shifted lower throughout the run. The increase in positive foot work may be attributed to increased foot joint work performed by intrinsic foot muscles. Changes in negative foot work and TA EMG frequency may indicate that the TA plays a role in negative foot work in the early stance of a run. CONCLUSION: This study is the first to examine how the kinetic contributions of the foot change throughout a run. Future studies should investigate how increases in foot work affect running performance.

Can changes in midsole bending stiffness of shoes affect the onset of joint work redistribution during a prolonged run?

PURPOSE: This study aimed to investigate if changing the midsole bending stiffness of athletic footwear can affect the onset of lower limb joint work redistribution during a prolonged run. METHODS: Fifteen trained male runners (10-km time of <44 min) performed 10-km runs at 90% of their individual speed at lactate threshold (i.e., when change in lactate exceeded 1 mmol/L during an incremental running test) in a control and stiff shoe condition on 2 occasions. Lower limb joint kinematics and kinetics were measured using a motion capture system and a force-instrumented treadmill. Data were acquired every 500 m. RESULTS: Prolonged running resulted in a redistribution of positive joint work from distal to proximal joints in both shoe conditions. Compared to the beginning of the run, less positive work was performed at the ankle (approximately 9%; p ≤ 0.001) and more positive work was performed at the knee joint (approximately 17%; p ≤ 0.001) at the end of the run. When running in the stiff shoe condition, the onset of joint work redistribution at the ankle and knee joints occurred at a later point during the run. CONCLUSION: A delayed onset of joint work redistribution in the stiff condition may result in less activated muscle volume, because ankle plantar flexor muscles have shorter muscles fascicles and smaller cross-sectional areas compared to knee extensor muscles. Less active muscle volume could be related to previously reported decreases in metabolic cost when running in stiff footwear. These results contribute to the notion that footwear with increased stiffness likely results in reductions in metabolic cost by delaying joint work redistribution from distal to proximal joints.

Systematic reduction of leg muscle activity throughout a standard assessment of running footwear.

PURPOSE: This study aimed to investigate whether there is a systematic change of leg muscle activity, as quantified by surface electromyography (EMG), throughout a standard running footwear assessment protocol at a predetermined running speed. METHODS: Thirty-one physically active adults (15 females and 16 males) completed 5 testing rounds consisting of overground running trials at a speed of 3.5 m/s. The level of muscle activity from 6 major leg muscles was recorded using surface EMG. The variables assessed were the EMG total intensity as a function of time and the cumulative EMG overall intensity. Systematic effects of the chronological testing round (independent variable) on the normalized EMG overall intensity (dependent variable) were examined using Friedman analysis of variates and post hoc pairwise Wilcoxon signed-rank tests (α = 0.05). RESULTS: There was a systematic reduction in overall EMG intensity for all 6 muscles over the time course of the running protocol (p < 0.001) until the fourth testing round when EMG intensities reached a steady state. The one exception was the biceps femoris muscle, which showed a significant reduction of EMG intensity during the stance phase (p < 0.001) but not the swing phase (p = 0.16). CONCLUSION: While running at a predetermined speed, the neuromuscular system undergoes an adaptation process characterized by a progressive reduction in the activity level of major leg muscles. This process may represent an optimization strategy of the neuromuscular system towards a more energetically efficient running style. Future running protocols should include a familiarization period of at least 7 min or 600 strides of running at the predetermined speed.

Isolating the Unique and Generic Movement Characteristics of Highly Trained Runners.

Human movement patterns were shown to be as unique to individuals as their fingerprints. However, some movement characteristics are more important than other characteristics for machine learning algorithms to distinguish between individuals. Here, we explored the idea that movement patterns contain unique characteristics that differentiate between individuals and generic characteristics that do not differentiate between individuals. Layer-wise relevance propagation was applied to an artificial neural network that was trained to recognize 20 male triathletes based on their respective movement patterns to derive characteristics of high/low importance for human recognition. The similarity between movement patterns that were defined exclusively through characteristics of high/low importance was then evaluated for all participants in a pairwise fashion. We found that movement patterns of triathletes overlapped minimally when they were defined by variables that were very important for a neural network to distinguish between individuals. The movement patterns overlapped substantially when defined through less important characteristics. We concluded that the unique movement characteristics of elite runners were predominantly sagittal plane movements of the spine and lower extremities during mid-stance and mid-swing, while the generic movement characteristics were sagittal plane movements of the spine during early and late stance.

Dr. Richard C. Nelson: A Facilitator and Door Opener.

Dr. Richard Nelson contributed to the development of sport biomechanics by being an international facilitator. Together with Dr. Jürg Wartenweiler, he contributed the necessary support and input that allowed the field of Movement and Sports Biomechanics to develop and flourish.

Comparison of two coupling methods regarding coupling patterns, sensitivity to footwear and potential future injury applications.

Researchers have quantified the effect of footwear conditions on movement patterns and injury risk for runners using discrete kinematic variables and/or relative coupling variables. Coupling is typically assessed using the transfer coefficient (TC) or the vector coding (VC) approach. However, a thorough comparison of both methods regarding their interpretation, sensitivity to testing conditions and information regarding coupling strength as one overall coupling score is missing. This study aimed to compare both methods regarding a) their coupling patterns, b) their sensitivity to footwear conditions and c) to discuss both coupling approaches regarding an overall coupling score. 3D motion capture data was collected of 10 males running on a treadmill with and without shoes. Rearfoot frontal and tibia transverse plane motion was analyzed. Discrete kinematic variables and relative coupling variables were calculated via the TC and VC approach for the landing and push-off phase. A novel variable, the coupling score, was developed and calculated using both coupling methods. Coupling variables calculated with both methods showed differences in coupling patterns, especially for the landing phase (TC ≈ 0.5/in-phase towards rearfoot-phase, VC ≈ 300°/anti-phase). VC offers further details, such as coupling frequencies, compared to the TC. Moreover, both methods were unable to distinguish between footwear conditions regarding their coupling patterns or coupling scores. Strong correlations (r ≤ 0.7, p < 0.0125) between coupling scores assessed with either method suggest that both methods contain similar information regarding coupling strength. The coupling score represents a first attempt to quantify a weighted coupling pattern quantitatively. Future studies have to validate whether the coupling score might be linked to injury risks.

Individuality decoded by running patterns: Movement characteristics that determine the uniqueness of human running.

Human gait is as unique to an individual as is their fingerprint. It remains unknown, however, what gait characteristics differentiate well between individuals that could define the uniqueness of human gait. The purpose of this work was to determine the gait characteristics that were most relevant for a neural network to identify individuals based on their running patterns. An artificial neural network was trained to recognize kinetic and kinematic movement trajectories of overground running from 50 healthy novice runners (males and females). Using layer-wise relevance propagation, the contribution of each variable to the classification result of the neural network was determined. It was found that gait characteristics of the coronal and transverse plane as well as medio-lateral ground reaction forces provided more information for subject identification than gait characteristics of the sagittal plane and ground reaction forces in vertical or anterior-posterior direction. Additionally, gait characteristics during the early stance were more relevant for gait recognition than those of the mid and late stance phase. It was concluded that the uniqueness of human gait is predominantly encoded in movements of the coronal and transverse plane during early stance.

The effects of shoe upper construction on mechanical ankle joint work during lateral shuffle movements.

Lateral shuffles are common movements in sports and are facilitated by the hip, knee, and ankle joints. Shoe uppers can change ankle kinetics during walking and running. However, it is not known how shoe upper modifications affect ankle kinetics during shuffling. The purpose of this study was to investigate the effects of shoe upper construction on mechanical ankle joint work during shuffling. It was hypothesized that a shoe with a reinforced upper will result in decreased negative ankle joint work. Twenty participants performed Maximal (MLST) and Submaximal Lateral Shuffle Tests (90% of MLST) in footwear with a minimal (MU) and reinforced upper (RU). Ground reaction forces and ankle kinematics were collected to compute ankle joint work. Performing lateral shuffles in the RU condition resulted in significantly reduced positive (MU: 0.62 ± 0.16 J/kg, RU: 0.55 ± 0.16 J/kg; p = 0.001, d = 0.44) and negative (MU: -0.60 ± 0.20 J/kg, RU: -0.53 ± 0.19 J/kg; p = 0.004, d = 0.41) ankle work. A decrease in positive and negative work could be a performance benefit, enabling the athlete to perform the same movement with a lower energy cost. More extreme upper interventions may yield even larger performance benefits.

Increasing the midsole bending stiffness of shoes alters gastrocnemius medialis muscle function during running.

In recent years, increasing the midsole bending stiffness (MBS) of running shoes by embedding carbon fibre plates in the midsole resulted in many world records set during long-distance running competitions. Although several theories were introduced to unravel the mechanisms behind these performance benefits, no definitive explanation was provided so far. This study aimed to investigate how the function of the gastrocnemius medialis (GM) muscle and Achilles tendon is altered when running in shoes with increased MBS. Here, we provide the first direct evidence that the amount and velocity of GM muscle fascicle shortening is reduced when running with increased MBS. Compared to control, running in the stiffest condition at 90% of speed at lactate threshold resulted in less muscle fascicle shortening (p = 0.006, d = 0.87), slower average shortening velocity (p = 0.002, d = 0.93) and greater estimated Achilles tendon energy return (p ≤ 0.001, d = 0.96), without a significant change in GM fascicle work (p = 0.335, d = 0.40) or GM energy cost (p = 0.569, d = 0.30). The findings of this study suggest that running in stiff shoes allows the ankle plantarflexor muscle-tendon unit to continue to operate on a more favourable position of the muscle's force-length-velocity relationship by lowering muscle shortening velocity and increasing tendon energy return.

Influence of running shoes on muscle activity.

Studies on the paradigm of the preferred movement path are scarce, and as a result, many aspects of the paradigm remain elusive. It remains unknown, for instance, how muscle activity adapts when differences in joint kinematics, due to altered running conditions, are of low / high magnitudes. Therefore, the purpose of this work was to investigate changes in muscle activity of the lower extremities in runners with minimal (≤ 3°) or substantial (> 3°) mean absolute differences in the ankle and knee joint angle trajectories when subjected to different running footwear. Mean absolute differences in the integral of the muscle activity were quantified for the tibialis anterior (TA), peroneus longus (PL), gastrocnemius medialis (GM), soleus (SO), vastus lateralis (VL), and biceps femoris (BF) muscles during over ground running. In runners with minimal changes in 3D joint angle trajectories (≤ 3°), muscle activity was found to change drastically when comparing barefoot to shod running (TA: 35%; PL: 11%; GM: 17%; SO: 10%; VL: 27%; BF: 16%), and minimally when comparing shod to shod running (TA: 10%; PL: 9%; GM: 13%; SO: 8%; VL: 8%; BF: 12%). For runners who showed substantial changes in joint angle trajectories (> 3°), muscle activity changed drastically in barefoot to shod comparisons (TA: 39%; PL: 14%; GM: 16%; SO: 16%; VL: 25%; BF: 24%). It was concluded that a movement path can be maintained with small adaptations in muscle activation when running conditions are similar, while large adaptations in muscle activation are needed when running conditions are substantially different.

The Effects of Increased Midsole Bending Stiffness of Sport Shoes on Muscle-Tendon Unit Shortening and Shortening Velocity: a Randomised Crossover Trial in Recreational Male Runners.

BACKGROUND: Individual compliances of the foot-shoe interface have been suggested to store and release elastic strain energy via ligamentous and tendinous structures or by increased midsole bending stiffness (MBS), compression stiffness, and resilience of running shoes. It is unknown, however, how these compliances interact with each other when the MBS of a running shoe is increased. The purpose of this study was to investigate how structures of the foot-shoe interface are influenced during running by changes to the MBS of sport shoes. METHODS: A randomised crossover trial was performed, where 13 male, recreational runners ran on an instrumented treadmill at 3.5 m·s-1 while motion capture was used to estimate foot arch, plantar muscle-tendon unit (pMTU), and shank muscle-tendon unit (sMTU) behaviour in two conditions: (1) control shoe and (2) the same shoe with carbon fibre plates inserted to increase the MBS. RESULTS: Running in a shoe with increased MBS resulted in less deformation of the arch (mean ± SD; stiff, 7.26 ± 1.78°; control, 8.84 ± 2.87°; p ≤ 0.05), reduced pMTU shortening (stiff, 4.39 ± 1.59 mm; control, 6.46 ± 1.42 mm; p ≤ 0.01), and lower shortening velocities of the pMTU (stiff, - 0.21 ± 0.03 m·s-1; control, - 0.30 ± 0.05 m·s-1; p ≤ 0.01) and sMTU (stiff, - 0.35 ± 0.08 m·s-1; control, - 0.45 ± 0.11 m·s-1; p ≤ 0.001) compared to a control condition. The positive and net work performed at the arch and pMTU, and the net work at the sMTU were significantly lower in the stiff compared to the control condition. CONCLUSION: The findings of this study showed that if a compliance of the foot-shoe interface is altered during running (e.g. by increasing the MBS of a shoe), the mechanics of other structures change as well. This could potentially affect long-distance running performance.