Colin W. Bond

Asymmetry of lower-extremity force and muscle activation during knee extension and functional tasks

Strength and power asymmetries of >10% may negatively impact physical function.

Occupational-Specific Strength Predicts Astronaut-Related Task Performance in a Weighted Suit

BACKGROUND Future space missions beyond low Earth orbit will require deconditioned astronauts to perform occupationally relevant tasks within a planetary spacesuit. The prediction of time-to-completion (TTC) of astronaut tasks will be critical for crew safety, autonomous operations, and mission success. This exploratory study determined if the addition of task-specific strength testing to current standard lower body testing would enhance the prediction of TTC in a 1-G test battery. METHODS Eight healthy participants completed NASA lower body strength tests, occupationally specific strength tests, and performed six task simulations (hand drilling, construction wrenching, incline walking, collecting weighted samples, and dragging an unresponsive crewmember to safety) in a 48-kg weighted suit. The TTC for each task was recorded and summed to obtain a total TTC for the test battery. Linear regression was used to predict total TTC with two models: 1) NASA lower body strength tests; and 2) NASA lower body strength tests + occupationally specific strength tests. RESULTS Total TTC of the test battery ranged from 20.2-44.5 min. The lower body strength test alone accounted for 61% of the variability in total TTC. The addition of hand drilling and wrenching strength tests accounted for 99% of the variability in total TTC. DISCUSSION Adding occupationally specific strength tests (hand drilling and wrenching) to standard lower body strength tests successfully predicted total TTC in a performance test battery within a weighted suit. Future research should couple these strength tests with higher fidelity task simulations to determine the utility and efficacy of task performance prediction.Taylor A, Kotarsky CJ, Bond CW, Hackney KJ. Occupational-specific strength predicts astronaut-related task performance in a weighted suit. Aerosp Med Hum Perform. 2018; 89(1):58-62.

Knee extensor power asymmetry is unrelated to functional mobility of older adults

Purpose: To determine whether knee extensor power asymmetry limits functional mobility of older adults who possess muscle weakness. Methods: Knee extensor power was measured in 36 older men and women (76.0 ± 7.6 yr), for each leg, on an isokinetic dynamometer at 60, 180, and 300 deg s−1 and power asymmetry was calculated as the percent difference in power between strong and weak legs, at each isokinetic velocity. 400‐m walk, stair ascent, and five‐repetition chair rise tests were performed to assess functional mobility. Pearson correlations were used to examine the relationship between weak leg power, strong leg power, power asymmetry, and 400‐m walk time, stair ascent time, and chair rise time. Participants were then stratified into low power‐high asymmetry (LP‐HA), low power‐low asymmetry (LP‐LA), high power‐high asymmetry (HP‐HA), and high power‐low asymmetry (HP‐LA) groups who were compared for functional mobility. Results: Knee extensor power asymmetry was unrelated to 400‐m walk time (r = 0.16, p = 0.180), stair ascent time (r = 0.22, p = 0.094), or chair rise time (r = 0.03, p = 0.437), whereas weak and strong leg powers were equally associated with 400‐m time (r = −0.62, p < 0.001; r = −0.62, p < 0.001), stair ascent time (r = −0.55, p < 0.001; r = −0.57, p < 0.001), and chair rise time (r = −0.28, p = 0.048; r = −0.31, p = 0.032), respectively. Power asymmetry was lowest at 60 deg s−1 (12%), and increased with contraction velocity (p = 0.001) to 15% at 180 deg s−1 and to 20% at 300 deg s−1. LP‐HA exhibited 26% slower 400‐walk time than HP‐LA (p = 0.015) and 19% slower than HP‐HA (p = 0.037). LP‐HA had 31% slower stair ascent time than HP‐LA (p = 0.033). There were no differences in chair rise performance between groups. Conclusions: Knee extensor power asymmetry was unrelated to 400‐m walk, stair ascent, and chair rise performance in older adults. Weak and strong limb powers were equally related to these functional measures, but a leftward shift of the power‐mobility curve exists for the weak leg that may hinder clinical assessment if strength or power is measured on a single limb and symmetry is assumed. The greatest degree of knee extensor power asymmetry occurred at the fastest isokinetic velocity, which suggests high‐speed muscle contractions may better differentiate laterality of function in older individuals. HighlightsAssociation between knee extensor power asymmetry and mobility was tested.Power asymmetry was unrelated to 400‐m walk, stair ascent and chair rise times.Strong and weak leg powers were equally related to mobility measures.Older adults with low power and high asymmetry had the poorest mobility.Power asymmetry increased with isokinetic test velocity.