Is My Exercise Partner Similar Enough? Partner Characteristics as a Moderator of the Köhler Effect in Exergames

Characterizing the relationship between peak assistance torque and metabolic cost reduction during running with ankle exoskeletons

BACKGROUND

Reducing the energy cost of running with exoskeletons could improve enjoyment, reduce fatigue, and encourage participation among novice and ageing runners. Previously, tethered ankle exoskeleton emulators with offboard motors were used to greatly reduce the energy cost of running with powered ankle plantarflexion assistance. Through a process known as "human-in-the-loop optimization", the timing and magnitude of assistance torque was optimized to maximally reduce metabolic cost. However, to achieve the maximum net benefit in energy cost outside of the laboratory environment, it is also necessary to consider the tradeoff between the magnitude of device assistance and the metabolic penalty of carrying a heavier, more powerful exoskeleton.

METHODS

In this study, tethered ankle exoskeleton emulators were used to characterize the effect of peak assistance torque on metabolic cost during running. Three recreational runners participated in human-in-the-loop optimization at four fixed peak assistance torque levels to obtain their energetically optimal assistance timing parameters at each level.

RESULTS

We found that the relationship between metabolic rate and peak assistance torque was nearly linear but with diminishing returns at higher torque magnitudes, which is well-approximated by an asymptotic exponential function. At the highest assistance torque magnitude of 0.8 Nm/kg, participants' net metabolic rate was 24.8 ± 2.3% (p = 4e-6) lower than running in the unpowered devices. Optimized timing of peak assistance torque was as late as allowed during stance (80% of stance) and optimized timing of torque removal was at toe-off (100% of stance); similar assistance timing was preferred across participants and torque magnitudes.

CONCLUSIONS

These results allow exoskeleton designers to predict the energy cost savings for candidate devices with different assistance torque capabilities, thus informing the design of portable ankle exoskeletons that maximize net metabolic benefit.

P-Curve Analysis of the Köhler Motivation Gain Effect in Exercise Settings: A Demonstration of a Novel Technique to Estimate Evidential Value Across Multiple Studies

BACKGROUND

Practitioners and researchers may not always be able to adequately evaluate the evidential value of findings from a series of independent studies. This is partially due to the possibility of inflated effect size estimates for these findings as a result of researcher manipulation or selective reporting of analyses (i.e., p-hacking). In light of the possible overestimation of effect sizes in the literature, the p-curve analysis has been proposed as a worthwhile tool that may help identify bias across a series of studies focused on a single effect. The p-curve analysis provides a measure of the evidential value in the published literature and might highlight p-hacking practices.

PURPOSE

Therefore, the purpose of this paper is to introduce the mechanics of the p-curve analysis to individuals researching phenomena in the psychosocial aspects of behavior and provide a substantive example of a p-curve analysis using findings from a series of studies examining a group dynamic motivation gain paradigm.

METHODS

We performed a p-curve analysis on a sample of 13 studies that examined the Köhler motivation gain effect in exercise settings as a means to instruct readers how to conduct such an analysis on their own.

RESULTS

The p-curve for studies examining the Köhler effect demonstrated evidential value and that this motivation effect is likely not a byproduct of p-hacking. The p-curve analysis is explained, as well as potential limitations of the analysis, interpretation of the results, and other uses where a p-curve analysis could be implemented.

Attenuation of the Köhler Effect in Racially Dissimilar Partnered Exercise Reversed Using Team Identity Strategy

The authors describe two research experiments exploring the influence of race on the Köhler motivation gain effect with exercise tasks. Experiment 1 tested whether partner racial dissimilarity affects individual performance. Experiment 2 created a team identity recategorization intervention to potentially counter the influence on performance observed in Experiment 1. White male participants were partnered with either a Black or Asian partner (Experiment 1) or with a Black partner utilizing team names and shirt colors as a team identity recategorization strategy (Experiment 2). Racially dissimilar dyads completed two sets of abdominal plank exercises with a Köhler conjunctive task paradigm (stronger partner; team performance outcome dependent upon the weaker-ability participant's performance). The results of Experiment 1 suggest attenuation of the previously successful group motivation gain effect in the racially dissimilar condition. The simple recategorization strategy utilized in Experiment 2 appeared to reverse motivation losses under conjunctive-task conditions in racially dissimilar exercise dyads.

Improving the energy economy of human running with powered and unpowered ankle exoskeleton assistance

Exoskeletons that reduce energetic cost could make recreational running more enjoyable and improve running performance. Although there are many ways to assist runners, the best approaches remain unclear. In our study, we used a tethered ankle exoskeleton emulator to optimize both powered and spring-like exoskeleton characteristics while participants ran on a treadmill. We expected powered conditions to provide large improvements in energy economy and for spring-like patterns to provide smaller benefits achievable with simpler devices. We used human-in-the-loop optimization to attempt to identify the best exoskeleton characteristics for each device type and individual user, allowing for a well-controlled comparison. We found that optimized powered assistance improved energy economy by 24.7 ± 6.9% compared with zero torque and 14.6 ± 7.7% compared with running in normal shoes. Optimized powered torque patterns for individuals varied substantially, but all resulted in relatively high mechanical work input (0.36 ± 0.09 joule kilogram^-1 per step) and late timing of peak torque (75.7 ± 5.0% stance). Unexpectedly, spring-like assistance was ineffective, improving energy economy by only 2.1 ± 2.4% compared with zero torque and increasing metabolic rate by 11.1 ± 2.8% compared with control shoes. The energy savings we observed imply that running velocity could be increased by as much as 10% with no added effort for the user and could influence the design of future products.

Intergroup Competition in Exergames: Further Tests of the Köhler Effect

OBJECTIVE

We examined how competing with a software-generated partner (SGP) against another human/virtual partner team, in an exercise video game (exergame), affects individual motivation as measured by effort.

MATERIALS AND METHODS

Participants (n = 90; 49 female; Mage = 19.93 ± 1.48) were randomly assigned to one of three conditions: individual control (IC); conjunctive partner, no competition (PNC); or conjunctive partner, with competition (PWC). Participants performed the first series of exercises alone. After resting, those in the partnered conditions performed the remaining trials with a same-sex SGP. Those in the PWC condition were told that they and their virtual partner would be competing against another human-virtual partner team.

RESULTS

A significant motivation gain was observed in both partnered conditions compared to control (P < 0.001), but the partnered groups did not differ significantly. However, participants in the PWC condition enjoyed the task significantly (P < 0.05) more than those in the PNC and IC conditions and the PWC participants identified more with the SGP as a teammate than the PNC participants.

CONCLUSIONS

Altogether, intergroup competition with an SGP may be an enjoyable way to enhance motivation and performance while exercising.

Introductory Dialogue and the Köhler Effect in Software-Generated Workout Partners

OBJECTIVES

This study explored the Köhler motivation gain effect utilizing adults and software-generated partners (SGPs) during an abdominal exercise regimen and compared the type of participant-SGP introductory dialogue as a moderator. The Köhler effect applies interdependent team dynamics in which group performance is dependent upon the weaker member. The third objective was to examine if this motivation paradigm would result in adverse consequences to secondary variables: exertion, enjoyment, and self-efficacy beliefs.

DESIGN

Adults (M_age = 38.8 +/- 7.7) were randomly assigned to 1 of 3 conditions: Interactive Partner SGP (IP), Linear Dialogue Partner SGP (LDP), or individual control (IC), to complete a series of abdominal exercises. The experiment used a 3 (condition) x 2 (gender) ANCOVA design, with a baseline block of exercises as a covariate.

METHOD

Participants completed abdominal exercises individually and, after a rest, repeated the same exercises with either an SGP programmed to be moderately stronger or individually (IC). Prior to the second exercise block, IP participants interacted with the SGP using a dialog tree optional-response format. The LDP participant introduction was a linear, scripted exchange of basic information.

RESULTS

The LDP and IP conditions persisted significantly longer than IC, generating moderate effect sizes (d = .62; d = .76). The mean difference between partnered conditions was not significant.

CONCLUSIONS

The Köhler motivation exercise paradigm resulted in a considerable increase in persistence (M_adj = 28.9, SE = 10.6) in the first study to use middle-aged adults with superior SGPs. Differences between introductory dialogue methods were not significant.

Cyber Buddy Is Better than No Buddy: A Test of the Köhler Motivation Effect in Exergames

OBJECTIVE

Although exergames are popular, few people take advantage of the potential of group dynamics to motivate play (and achieve associated health benefits). One motivation gain phenomenon has shown promise for motivating greater effort in partnered exergames: The Köhler effect (working at a task with a more capable partner where one's performance is indispensable to the group). This article examines whether a Köhler effect can be demonstrated in an exergame by exercising with a moderately superior humanoid, software-generated partner.

MATERIALS AND METHODS

Male and female (n=120; mean age, 19.41 years) college students completed a series of plank exercises using "CyBuddy Exercise," a program developed specifically for this study. In a lab in an academic building, participants completed the exercises individually and, after a rest, were randomly assigned to complete the same exercises again, but with a "live" human partner (HP) presented virtually, a nearly-human-like, humanoid partner (NHP), a hardly human-like, software-generated partner (HHP), or a no-partner control condition (IC), with equal numbers in each group (i.e., n=30). Exercise persistence, perceived exertion, self-efficacy beliefs, enjoyment, and intentions to exercise were recorded and analyzed.

RESULTS

A 4×2 analysis of variance on the (Block 2 - Block 1) difference scores showed that a significant Köhler motivation gain was observed in all partner conditions (compared with IC), but persistence was significantly greater with HPs than with either NHP or HHP humanoid partners (P<0.05). By the conclusion of the study, there were no significant differences among the partnered conditions in perceived exertion, self-efficacy, enjoyment, or future intentions to exercise.

CONCLUSIONS

These results suggest that a software-generated partner can elicit the Kőhler motivation gain in exergames, but not as strongly as a partner who is thought to be human.