Rodger Kram

University of Colorado Boulder | CUB · Department of Integrative Physiology

Aim: We analyzed the biomechanical response (joint angles, moments, and powers) to running with added leg mass. These data may help guide the design of wearable locomotor assistive devices (i.e., exoskeletons), which are becoming more prevalent. Methods: 15 participants (7 females, 8 males) completed treadmill running trials (3m•s-1) normally an...

Background: Wearable exoskeletal devices can enhance locomotor performance, but their mass results in a metabolic penalty. Previous studies have quantified the metabolic cost of running with added mass on the feet, but less is known about the effects of adding mass to the thigh and shank segments. Aim: To quantify the metabolic cost of running w...

Physiologists commonly use single-value energy equivalents (e.g. 20.1 kJ/LO2 and 20.9 kJ/LO2) to convert oxygen uptake (V̇O2) to energy, but doing so ignores how substrate oxidation (carbohydrate:fat) changes across aerobic intensities. However, 20.1 kJ/O2 is an outdated value and using either 20.1 kJ/O2 or 20.9 kJ/O2 can incur systematic errors of...

Recently developed shoes that are highly-cushioned and have a curved stiff plate embedded in the midsole are “ergogenic” in that they reduce the rate of metabolic energy required to run at a defined speed. These energy savings are not due to low mass but rather to their foam midsoles which are unusually compliant and resilient. The function of the...

A total of 200,000+ large timbers were transported >75 km to Chaco Canyon, a political and religious center in the precontact U.S. Southwest, using only human power. Previous researchers reported that typical primary roof beams (vigas) of Chacoan Great Houses averaged 0.22 m in diameter and 5 m in length with a mass of 275 kg. However, the 275 kg m...

The benefits of drafting for elite marathon runners are intuitive, but the quantitative energetic and time savings are still unclear due to the different methods used for converting aerodynamic drag force reductions to gross metabolic power savings. Further, we lack a mechanistic understanding of the relationship between aerodynamic drag forces and...

Triathletes almost universally use two shoe types; one for cycling and one for running. Though equally as efficient as cycling shoes during steady-state cycling, traditional running shoes impair cycling sprint performance. Newly developed running shoes, containing stiff carbon-fibre plates, may allow triathletes to use one pair of shoes for both cy...

Riding uphill presents a challenge to competitive and recreational cyclists. Based on only limited evidence, some scientists have reported that tilting the saddle nose down improves uphill-cycling efficiency by as much as 6%. Purpose: here, we investigated if simply tilting the saddle nose down increases efficiency during uphill cycling, which wo...

Background: Compared to conventional racing shoes, Nike Vaporfly 4% running shoes reduce the metabolic cost of level treadmill running by 4%. The reduction is attributed to their lightweight, highly compliant, and resilient midsole foam and a midsole-embedded curved carbon fiber plate. We investigated whether these shoes also reduce the metabolic...

does rocking a bike produces more power?

Riding uphill presents a challenge to competitive and recreational cyclists. Based on only limited evidence, some scientists have reported that tilting the saddle nose down improves uphill-cycling efficiency by as much as 6%. Purpose: Here, we investigated if simply tilting the saddle nose down increases efficiency during uphill cycling, which woul...

Competitive cyclists typically sprint out of the saddle and alternately lean their bikes from side to side, away from the downstroke pedal. Yet, there is no direct evidence as to whether leaning the bicycle or conversely, attempting to minimize lean, affects maximal power output during sprint cycling. Here, we modified a cycling ergometer so that i...

We lack a mechanistic understanding of the relationship between aerodynamic drag forces and metabolic power during running. Further, the energetic and time savings possible from reducing aerodynamic drag (drafting) are still unclear due to the different methods previously assumed for converting from force reductions to metabolic power savings. Here...

Competitive cyclists typically sprint out of the saddle and alternately lean their bikes from side-to-side, away from the downstroke pedal. Yet, there is no direct evidence as to whether leaning the bicycle, or conversely, attempting to minimize lean, affects maximal power output during sprint cycling. Here, we modified a cycling ergometer so that...

Humans prefer to walk at slow speeds and to run at fast speeds. In between, there is a speed at which people choose to transition between gaits, the Preferred Transition Speed (PTS). At slow speeds, it is energetically cheaper to walk and at faster speeds, it is cheaper to run. Thus, there is an intermediate speed, the Energetically Optimal Transit...

Eliud Kipchoge made two attempts to break the 2-hour marathon, in Monza and then Vienna. Here we analyse only the effects of course elevation profile and turn curvatures on his performances. We used publicly available data to determine the undulations in elevation and the radii of the curves on the course. With previously developed equations for th...

Most competitive and recreational road cyclists use stiff-soled shoes designed for cycling and ‘clipless’ pedals that firmly attach to the shoes. There are many unsubstantiated claims by cyclists and industry professionals about the advantages of cycling shoes and clipless pedals. Scientific research has shown that cycling shoes and clipless pedals...

PurposeWe sought to biomechanically distinguish steep uphill running from steep uphill walking and explore why athletes alternate between walking and running on steep inclines.Methods We quantified vertical center of mass (COM) accelerations and basic stride parameters for both walking and running at a treadmill speed of 1.0 m/s on the level and up...

Humans prefer to walk at slow speeds and to run at fast speeds. In between, there is a speed at which people choose to transition between gaits, the Preferred Transition Speed (PTS). At slow speeds, it is energetically cheaper to walk and at faster speeds, it is cheaper to run. Thus, there is an intermediate speed, the Energetically Optimal Transit...

Most competitive and recreational road cyclists use stiff-soled shoes designed for cycling and “clipless” pedals that firmly attach to the shoes. There are many unsubstantiated claims by cyclists and industry professionals about the advantages of cycling shoes and clipless pedals. Scientific research has shown that cycling shoes and clipless pedals...

Cyclists and industry professionals believe that cycling shoes with pedal attachment and stiff soles improve performance. However, scientific evidence has demonstrated that cycling shoes have no significant effect on metabolic cost during low-intensity, submaximal, steady-state cycling (50–150 W). Here, we investigated if stiff-soled cycling shoes...

Background Although straight ahead running appears to be faster, distance running races are predominately contested on tracks or roads that involve curves. How much faster could world records be run on straight courses? Methods Here,we propose a model to explain the slower times observed for races involving curves compared to straight running. For...

Eliud Kipchoge is scheduled to attempt to run a marathon in 1:59:59 or faster on October 12, 2019. We used publicly available data to determine the undulations in elevation and the radii of the curves on the course. With previously developed equations for the effects of velocity, slope, and curvature on oxygen uptake, we performed simulations to qu...

Background On a curve, the average axial leg force (F a ) of a runner is increased due to the need to exert centripetal force. The increased F a presumably requires a greater rate of metabolic energy expenditure than straight running at the same velocity. We propose a model that explains the velocity reduction on curves, compared to straight runnin...

Background On a curve, the average axial leg force (F a ) of a runner is increased due to the need to exert centripetal force. The increased F a presumably requires a greater rate of metabolic energy expenditure than straight running at the same velocity. We propose a model that explains the velocity reduction on curves, compared to straight runnin...

Cyclists and industry professionals believe that cycling shoes improve performance. However, scientific evidence has demonstrated that cycling shoes have no significant effect on metabolic cost during submaximal, steady-state cycling (50-150 W). Here, we investigated if cycling shoes and click-in pedals provide benefits relevant to sprint cycling....

Purpose In trail running and in uphill races many athletes use poles. However, there are few data about pole walking on steep uphill. The aim of this study was to compare the energy expenditure during uphill walking with (PW) and without (W) poles at different slopes. Methods Fourteen mountain running athletes walked on a treadmill in two conditio...

Background: In laboratory settings, cycling workstations improve cardiometabolic risk factors. Our purpose was to quantify risk factors following a cycling intervention in the workplace. Methods: Twenty-one office workers who sat at work ≥6 hours per day underwent baseline physiological measurements (resting blood pressure, blood lipid profile,...

Humans have evolved the ability to walk very efficiently. Further, humans prefer to walk at speeds that approximately minimize their metabolic energy expenditure per unit distance (i.e. gross cost of transport, COT). This has been found in a variety of population groups and other species. However, these studies were mostly performed on smooth, leve...

Training, footwear, nutrition, and racing strategies (i.e., drafting) have all been shown to reduce the metabolic cost of distance running (i.e., improve running economy). However, how these improvements in running economy (RE) quantitatively translate into faster running performance is less established. Here, we quantify how metabolic savings tran...

Purpose Exercise economy is not solely an intrinsic physiological trait because economy in one mode of exercise (e.g., running) does not strongly correlate with economy in another mode (e.g. cycling). Economy also reflects the skill of an individual in a particular mode of exercise. Arguably, level, uphill and downhill running constitute biomechani...

Background We have shown that a prototype marathon racing shoe reduced the metabolic cost of running for all 18 participants in our sample by an average of 4%, compared to two well-established racing shoes. Gross measures of biomechanics showed minor differences and could not explain the metabolic savings. Objective To explain the metabolic saving...

The cost of generating force hypothesis proposes that the metabolic rate during running is determined by the rate of muscle force development (1/tc, tc=contact time) and the volume of active leg muscle. A previous study assumed a constant recruited muscle volume and reported that the rate of force development alone explained ∼70% of the increase in...

Purpose: Exercise economy is one of the main physiological factors determining performance in endurance sports. Running economy (RE) can be improved with running-specific training, while the improvement of cycling economy (CE) with cycling-specific training is controversial. We investigated whether exercise economy reflects sport-specific skills/a...

Humans naturally select several parameters within a gait that correspond with minimizing metabolic cost. Much less is understood about the role of metabolic cost in selecting between gaits. Here, we asked participants to decide between walking or running out and back to different gait specific markers. The distance of the walking marker was adjuste...

An Online First version of this article was made available online at https://link.springer.com/article/10.1007/s40279-017-0811-2 on 16 November 2017. An error was subsequently identified in the article, and the following correction should be noted.

Humans have evolved the ability to walk very efficiently. Further, humans prefer to walk at speeds that approximately minimize their metabolic energy expenditure per unit distance (i.e. gross cost of transport, COT). This has been found in a variety of population groups and other species. However, these studies were performed on smooth, level groun...

Background Reducing the energetic cost of running seems the most feasible path to a sub-2-hour marathon. Footwear mass, cushioning, and bending stiffness each affect the energetic cost of running. Recently, prototype running shoes were developed that combine a new highly compliant and resilient midsole material with a stiff embedded plate. Objectiv...

We compared ten published equations for calculating energy expenditure from oxygen consumption and carbon dioxide production using data for 10 high-caliber male distance runners over a wide range of running velocities. We found up to a 5.2% difference in calculated metabolic rate between two widely used equations. We urge our fellow researchers aba...

Running economy (oxygen uptake or metabolic rate for running at a submaximal speed) is one of the key determinants of distance running performance. Previous studies reported linear relationships between oxygen uptake or metabolic rate and speed, and an invariant cost of transport across speed. We quantified oxygen uptake, metabolic rate, and cost o...

Purpose: Historically, the efficiency of leg cycling has been difficult to change. However, arm cycling research indicates that relative crank angle changes can improve efficiency. Therefore, we investigated if leg cycling with different relative crank angles affects efficiency. Methods: Ten healthy, male, recreational bicycle riders (27.8 ± 8.2...

A sub-2-hour marathon requires an average velocity (5.86 m/s) that is 2.5% faster than the current world record of 02:02:57 (5.72 m/s) and could be accomplished with a 2.7% reduction in the metabolic cost of running. Although supporting body weight comprises the majority of the metabolic cost of running, targeting the costs of forward propulsion an...

Purpose: Vertical kilometer (VK) races, in which runners gain 1000 m of elevation in <5000 m of distance, are becoming popular. However, few studies on steep uphill running (>25°) exist. Previously, we determined that ~30° is the optimal angle for uphill running, costing the least amount of metabolic energy for a specific vertical velocity. To inf...

Athletes in the 3,000 m steeplechase track and field event negotiate unmovable hurdles and waterjumps. Ground reaction forces (GRF) in the steeplechase were quantified to elucidate injury risks / mechanisms and to inform coaches. Five male and five female steeplechasers participated. GRF were measured during treadmill running, and using specially m...

Introduction Pedelecs are bicycles that provide electric assistance only when a rider is pedaling and have become increasingly popular. Purpose Our purpose was to quantify usage patterns over 4 weeks of real-world commuting with a pedelec and to determine if pedelec use would improve cardiometabolic risk factors. Methods Twenty sedentary commuters...

Purpose: Our goal was to quantify if small (1 - 3%) changes in running economy quantitatively affect distance-running performance. Based on the linear relationship between metabolic rate and running velocity and on earlier observations that added shoe mass increases metabolic rate by ~1% per 100 grams per shoe, we hypothesized that adding 100 and...

Purpose: To quantify how acute passive cycling affects glucose and insulin responses to an oral glucose tolerance test (OGTT) and basic cognition compared to sitting and moderate-intensity active cycling. Methods: Twenty-four physically inactive healthy males completed three trials in randomized order involving 30-minute conditions of sitting, p...

On curves, non-amputees' maximum running speed is slower on smaller radii and thought to be limited by the inside leg's mechanics. Similar speed decreases would be expected for non-amputees in both counterclockwise and clockwise directions because they have symmetric legs. However, sprinters with unilateral leg amputation have asymmetric legs, whic...

Cyclists, coaches, and equipment manufacturers claim that cycling-specific shoes coupled with clipless pedals are ‘more efficient’. However, scientific evidence supporting or refuting these claims is lacking. We measured the metabolic cost of cycling at sub-maximal power outputs and tested the null hypothesis that there would be no differences betw...

Vertical kilometer foot races consist of a 1,000 m elevation gain in less than 5,000 m of overall distance and the inclines of the fastest courses are ~30°. Previous uphill locomotion studies have focused on much shallower angles. We aimed to quantify the metabolic costs of walking and running on very steep angles and to biomechanically distinguish...

Purpose: Sixty-five years of age typically marks the onset of impaired walking economy. However, running economy has not been assessed beyond the age of 65 years. Furthermore, a critical determinant of running economy is the spring-like storage and return of elastic energy from the leg during stance, which is related to leg stiffness. Therefore, w...

This study examined the effects of speed and leg prostheses on mediolateral (ML) foot placement and its variability in sprinters with and without transtibial amputations. We hypothesized that ML foot placement variability would: 1. increase with running speed up to maximum speed and 2. be symmetrical between the legs of non-amputee sprinters but as...

Introduction: Impaired walking performance is a key predictor of morbidity among older adults. A distinctive characteristic of impaired walking performance among older adults is a greater metabolic cost (worse economy) compared to young adults. However, older adults who consistently run have been shown to retain a similar running economy as young...

In the 2012 Paralympic 100 m and 200 m finals, 86% of athletes with a unilateral amputation placed their unaffected leg on the front starting block. Can this preference be explained biomechanically? We measured the biomechanical effects of starting block configuration for seven nonamputee sprinters and nine athletes with a unilateral amputation. Ea...

Mechanical energy is conserved during terrestrial locomotion in two ways; the inverted pendulum mechanism for walking and the spring-mass mechanism for running. Here, we investigated if diagonal stride cross-country roller skiing (DIA) utilizes similar mechanisms. Based on previous studies, we hypothesized that running and DIA would share similar p...

When moving slowly, kangaroos plant their tail on the ground in sequence with their front and hind legs. To determine the tail's role in this 'pentapedal' gait, we measured the forces the tail exerts on the ground and calculated the mechanical power it generates. We found that the tail is responsible for as much propulsive force as the front and hi...

Although the mechanical function is quite clear, there is no consensus regarding the metabolic benefit of arm swing during human running. We compared the metabolic cost of running using normal arm swing with the metabolic cost of running while restricting the arms in three different ways: (1) holding the hands with the arms behind the back in a rel...

Historically, several different approaches have been applied to explain the metabolic cost of uphill human running. Most of these approaches result in unrealistically high values for the efficiency of performing vertical work during running uphill, or are only valid for running up steep inclines. The purpose of this study was to reexamine the metab...

Compared with other species, humans can be very tractable and thus an ideal "model system" for investigating the metabolic cost of locomotion. Here, we review the biomechanical basis for the metabolic cost of running. Running has been historically modeled as a simple spring-mass system whereby the leg acts as a linear spring, storing, and returning...

This study aimed to investigate the effects of surface and shoe cushioning on the metabolic cost of running. In running, the leg muscles generate force to cushion the impact with the ground. External cushioning (surfaces or shoes) may reduce the muscular effort needed for cushioning and thus reduce metabolic cost. Our primary hypothesis was that th...

It has been suggested that the uniquely large gluteus maximus (GMAX) muscles were an important adaptation during hominin evolution based on numerous anatomical differences between humans and extant apes. GMAX electromyographic (EMG) signals have been quantified for numerous individual movements, but not across the range of locomotor gaits and speed...

In the 2012 Paralympic 100m and 200m finals, 86% of athletes with a unilateral amputation placed their unaffected leg on the front starting block. Can this preference be explained biomechanically? We measured the biomechanical effects of starting block configuration for seven non-amputee sprinters and nine athletes with a unilateral amputation. Eac...

In this paper, we study dynamic stability during running, focusing on the effects of speed, and the use of a leg prosthesis. We compute and compare the maximal Lyapunov exponents of kinematic time-series data from subjects with and without unilateral transtibial amputations running at a wide range of speeds. We find that the dynamics of the affecte...