30Forefoot running is advocated to improve running economy because of increased elastic energy 31 storage than rearfoot running. This claim has not been assessed with methods that predict the 32 elastic energy contribution to positive work or estimate muscle metabolic cost. The purpose of 33 this study was to compare the mechanical work and metabolic cost of the gastrocnemius and 34 soleus between rearfoot and forefoot running. Seventeen rearfoot and seventeen forefoot runners 35 ran over-ground with their habitual footfall pattern (3.33-3.68m•sP -1 P) while collecting motion 36 capture and ground reaction force data. Ankle and knee joint angles and ankle joint moments 37 served as inputs into a musculoskeletal model that calculated the mechanical work and metabolic 38 energy expenditure of each muscle using Hill-based muscle models with contractile (CE) and 39 series elastic (SEE) elements. A mixed-factor ANOVA assessed the difference between footfall 40 patterns and groups (α=0.05). Forefoot running resulted in greater SEE mechanical work in the 41 gastrocnemius than rearfoot running but no differences were found in CE mechanical work or 42 CE metabolic energy expenditure. Forefoot running resulted in greater soleus SEE and CE 43 mechanical work and CE metabolic energy expenditure than rearfoot running. The metabolic 44 cost associated with greater CE velocity, force production, and activation during forefoot running 45 may outweigh any metabolic energy savings associated with greater SEE mechanical work. 46

Background. Minimization of the energetic cost of transport (CoT) has been suggested for the walk-run transition in human locomotion. More recent literature argues that lower leg muscle activities are the potential triggers of the walk-run transition. We examined both metabolic and muscular aspects for explaining walk-run transition under body weight support (BWS; supported 30% of body weight) and normal walking (NW), because the BWS can reduce both leg muscle activity and metabolic rate. Methods. Thirteen healthy young males participated in this study. The energetically optimal transition speed (EOTS) was determined as the intersection between linear CoT and speed relationship in running and quadratic CoT-speed relationship in walking under BWS and NW conditions. Preferred transition speed (PTS) was determined during constant acceleration protocol (velocity ramp protocol at 0.00463 m•sec-2 (1 km•h-1 per minute) starting from 1.11 m•s-1. Muscle activities and mean power frequency (MPF) were measured using electromyography of the primary ankle dorsiflexor (tibialis anterior; TA) and synergetic plantar flexors (calf muscles including soleus) before and after the walk-run transition. Results. The EOTS was significantly faster than the PTS under both conditions, and both were faster under BWS than in NW. In both conditions, MPF decreased after the walk-run transition in the dorsiflexor and the combined plantar flexor activities, especially the soleus. Discussion. The walk-run transition is not triggered solely by the minimization of whole-body energy expenditure. Walk-run transition is associated with reduced TA and soleus activities with evidence of greater slow twitch fiber recruitment, perhaps to avoid early onset of localized muscle fatigue.

Background. Minimization of the energetic cost of transport (CoT) has been suggested for the walk-run transition in human locomotion. More recent literature argues that lower leg muscle activities are the potential triggers of the walk-run transition. We examined both metabolic and muscular aspects for explaining walk-run transition under body weight support (BWS; supported 30% of body weight) and normal walking (NW), because the BWS can reduce both leg muscle activity and metabolic rate.Methods. Thirteen healthy young males participated in this study. The energetically optimal transition speed (EOTS) was determined as the intersection between linear CoT and speed relationship in running and quadratic CoT-speed relationship in walking under BWS and NW conditions. Preferred transition speed (PTS) was determined during constant acceleration protocol (velocity ramp protocol at 0.00463 m·sec -2(1 km·h -1 per minute) starting from 1.11 m·s -1 . Muscle activities and mean power frequency (MPF) were measured using electromyography of the primary ankle dorsiflexor (tibialis anterior; TA) and synergetic plantar flexors (calf muscles including soleus) before and after the walk-run transition.Results. The EOTS was significantly faster than the PTS under both conditions, and both were faster under BWS than in NW. In both conditions, MPF decreased after the walk-run transition in the dorsiflexor and the combined plantar flexor activities, especially the soleus.Discussion. The walk-run transition is not triggered solely by the minimization of whole-body energy expenditure. Walk-run transition is associated with reduced TA and soleus activities with evidence of greater slow twitch fiber recruitment, perhaps to avoid early onset of localized muscle fatigue. Abstract 17 Background. Minimization of the energetic cost of transport (CoT) has been suggested for the 18 walk-run transition in human locomotion. More recent literature argues that lower leg muscle 19 activities are the potential triggers of the walk-run transition. We examined both metabolic and 20 muscular aspects for explaining walk-run transition under body weight support (BWS; supported 21 30% of body weight) and normal walking (NW), because the BWS can reduce both leg muscle 22 activity and metabolic rate. 23 Methods. Thirteen healthy young males participated in this study. The energetically optimal 24 transition speed (EOTS) was determined as the intersection between linear CoT and speed 25 relationship in running and quadratic CoT-speed relationship in walking under BWS and NW 26 conditions. Preferred transition speed (PTS) was determined during constant acceleration 27 protocol (velocity ramp protocol at 0.00463 m·sec -2 (1 km·h -1 per minute) starting from 1.11 m·s -28 1 . Muscle activities and mean power frequency (MPF) were measured using electromyography of 29 the primary ankle dorsiflexor (tibialis anterior; TA) and synergetic plantar flexors (calf muscles 30 including soleus) before and after the walk-run transition. 31 Results. The EOTS was significantly fa...

Background. Minimization of the energetic cost of transport (CoT) has been suggested for the walk-run transition in human locomotion. More recent literature argues that lower leg muscle activities are the potential triggers of the walk-run transition. We examined both metabolic and muscular aspects for explaining walk-run transition under body weight support (BWS; supported 30% of body weight) and normal walking (NW), because the BWS can reduce both leg muscle activity and metabolic rate. Methods. Thirteen healthy young males participated in this study. The energetically optimal transition speed (EOTS) was determined as the intersection between linear CoT and speed relationship in running and quadratic CoT-speed relationship in walking under BWS and NW conditions. Preferred transition speed (PTS) was determined during constant acceleration protocol (velocity ramp protocol at 0.00463 m•sec-2 (1 km•h-1 per minute) starting from 1.11 m•s-1. Muscle activities and mean power frequency (MPF) were measured using electromyography of the primary ankle dorsiflexor (tibialis anterior; TA) and synergetic plantar flexors (calf muscles including soleus) before and after the walk-run transition. Results. The EOTS was significantly faster than the PTS under both conditions, and both were faster under BWS than in NW. In both conditions, MPF decreased after the walk-run transition in the dorsiflexor and the combined plantar flexor activities, especially the soleus. Discussion. The walk-run transition is not triggered solely by the minimization of whole-body energy expenditure. Walk-run transition is associated with reduced TA and soleus activities with evidence of greater slow twitch fiber recruitment, perhaps to avoid early onset of localized muscle fatigue.

A summary is presented of five mechanical parameters from human lower limb skeletal muscles critical for Hill-based muscle modeling: the optimal fiber length, the fiber pennation angle, the physiological cross-sectional area (PCSA), the unloaded tendon length, and the fast-twitch fiber fraction. The data presented are drawn from a total of 29 publications including human cadaver studies, in vivo imaging studies of live humans, musculoskeletal modeling studies, and combinations of these methods. Where possible, parameter values were adjusted from the referenced data to present them with consistent definitions (normalization of measured fiber lengths to optimal sarcomere length, and calculation of PCSA as the ratio of fiber volume to fiber length). It is seen that within a specific muscle, optimal fiber lengths are fairly consistent between studies, pennation angles and PCSAs vary widely between studies, and data for unloaded tendon length are comparatively sparse. Few studies have reported fiber type fractions for a large number of muscles. Guidelines for implementing these parameter values in muscle modeling and musculoskeletal modeling are suggested.Update HistoryDecember 2, 2016: original submissionDecember 3, 2016: discussion on maximum isometric force and specific tension addedDecember 6, 2016: minor edits for typos, clarity, and missing referencesDecember 7, 2016: Tirrell et al. (2012) study added