The impact of age on muscle and kinematic responses following an unpredictable forward slip while walking.

Older adults displayed greater relative muscle activity during walking prior to slip onset compared to young adults.

• Cross-sectional study with 127 adults: 25 young and 102 older adults
• Bilateral lower limb muscle activity was measured via electromyography
• Greater relative muscle activity in older adults was statistically significant (P < 0.05)
• This finding was observed during normal walking before the slip was induced

Older adults had a higher relative centre of mass during walking prior to slip onset compared to young adults.

• Gait kinematics were measured via motion capture
• Difference in relative centre of mass height was statistically significant (P < 0.05)
• This measure was assessed during the pre-slip walking phase
• A higher centre of mass position may contribute to greater instability during a slip

Following the slip, older adults experienced slips with greater velocity than young adults.

• The slip was induced unpredictably at foot-strike while walking
• Greater slip velocity in older adults was statistically significant (P < 0.05)
• Greater slip velocity indicates more severe slip events in older adults
• This occurred despite identical slip induction conditions across age groups

Older adults displayed longer muscle onset latency and time to peak activity of the hamstrings on the non-slipped (contralateral) limb following the slip.

• Hamstring muscles serve as knee flexors and hip extensors on the contralateral limb
• Both onset latency and time to peak activity were significantly longer in older adults (P < 0.05)
• The contralateral limb is the recovery limb in a forward slip scenario
• Delayed activation of contralateral knee flexors and hip extensors may lead to greater instability

Older adults showed greater peak activity magnitudes of the gastrocnemius bilaterally following the slip.

• Bilateral gastrocnemius peak activity was greater in older adults (P < 0.05)
• This finding applied to both the slipped and non-slipped limbs
• Electromyography was used to measure muscle activity
• Greater gastrocnemius activation may reflect a compensatory or less coordinated neuromuscular response

Older adults spent more time in double-limb stance during slip recovery compared to young adults.

• Difference in double-limb stance time was statistically significant (P = 0.001)
• This kinematic measure was assessed via motion capture
• Prolonged double-limb stance may reflect slower or less effective recovery strategies
• This was one of several kinematic indicators of inferior slip recovery in older adults

Older adults took a slower second recovery step following the slip compared to young adults.

• Difference in second recovery step velocity was statistically significant (P = 0.006)
• Recovery step kinematics were assessed via motion capture
• A slower second recovery step indicates reduced ability to rapidly restore stable gait
• This finding was part of a broader pattern of inferior kinematic recovery responses in older adults

Older adults displayed greater harness loading following the slip compared to young adults.

• Difference in harness loading was statistically significant (P = 0.005)
• Harness loading is an indicator of fall severity or loss of balance requiring external support
• All participants were equipped with a safety harness during the slip perturbation protocol
• Greater harness loading in older adults reflects more severe balance loss following the slip