Vitamin D Supplementation and Muscle Function in Older Adults

Lower extremity muscle power will be measured at baseline, 4- and 12-month follow-up using the Nottingham Power Rig. Participants sit in a chair and unilaterally depress a foot lever attached to a flywheel as hard and as fast as they can. Power output, derived from the acceleration of the flywheel from 5 trials on each leg at maximal effort, will be recorded in Watts. Maximum leg power at baseline (from either the right or left leg) and the maximum power from the same leg at 4- and 12-month follow-up will be used in all analyses. Leg power (Watts) will be standardized to total body mass (in Kg).

This will be examined in muscle biopsies collected at baseline and 4-month follow-up using the ATPase, pH 9.4 technique, combined with laminin immunostaining in 10 micrometer muscle sections and the number of type I and type II fiber subtypes quantified. The percentage of type II fibers is calculated by dividing the number of type II fibers by the sum of type I and type II fibers combined.

Lower extremity muscle strength will be measured using an isokinetic dynamometer (Biodex) at one speed (60°/sec) with the participant sitting and the hips and knee flexed at 90°. Participants extend the knee and push as hard as possible against the resistance pad. Strength is expressed as peak torque in Newton-meters (Nm). The maximum knee extensor strength of the 4 repetitions from trial 2 for the dominant leg will be will be used in analyses unless unable to test the dominant leg (i.e., knee replacement) in which case the non-dominant leg will be used; the maximum knee extensor strength from the same leg will be used at 4- and 12-month follow-up for all analyses.

The short physical performance battery consists of standing balance (side-by-side, semi- and full-tandem stands for 10 seconds), a 4-m walk to assess usual gait speed, and 5 repeated chair stands at baseline, 4-months and 12-months. Each of the three performance measures is assigned a score ranging from 0 (inability to perform the task) to 4 (the highest level of performance) and summed to create an SPPB score ranging from 0 to 12 (best).

The expanded physical performance battery consists of standing balance (semi- and full-tandem stands and a single leg stand for 30 seconds), a 4-m walk to assess usual gait speed, a narrow 4-m walk test of balance (walking at usual pace within lines of tape spaced 20 cm apart), and 5 repeated chair stands at baseline, 4-months, and 12-months. Scores range from 0 to 4 with higher scores indicative of better physical performance.

The timed up and go will be measured by how long it takes (sec) to stand up from a chair, walk 3 m, turn around, walk back to the chair, and sit down at baseline, 4-months, and 12-months. Longer times to complete the TUG are indicative of greater fall risk.

Postural sway during quiet stance will be assessed from Center-of-Pressure (COP) trajectory data collected at 100 Hz using an Advanced Mechanical Technology Incorporated (AMTI) AccuSway biomechanics force platform at baseline, 4-months, and 12-months. Participants stand on the force platform barefoot in an upright stance with arms relaxed comfortably at their sides, eyes open, feet abducted 10 degrees, and heels separated medio-laterally by 6 cm. COP data is collected in a series of 10 30-sec trials standing on the force plate. Average sway velocity is measured in cm/sec. A higher number indicates more postural sway.

Postural sway during quiet stance will be assessed from Center-of-Pressure (COP) trajectory data collected at 100 Hz using an Advanced Mechanical Technology Incorporated (AMTI) AccuSway biomechanics force platform at baseline, 4-months, and 12-month. Participants stand on the force platform barefoot in an upright stance with arms relaxed comfortably at their sides, eyes open, feet abducted 10 degrees, and heels separated medio-laterally by 6 cm. COP data is collected in a series of 10 30-sec trials standing on the force plate. 95% confidence ellipse area is measured in cm squared. A higher number indicates more postural sway.

Postural sway during quiet stance will be assessed from Center-of-Pressure (COP) trajectory data collected at 100 Hz using an Advanced Mechanical Technology Incorporated (AMTI) AccuSway biomechanics force platform at baseline, 4-months, and 12-months. Participants stand on the force platform barefoot in an upright stance with arms relaxed comfortably at their sides, eyes open, feet abducted 10 degrees, and heels separated medio-laterally by 6 cm. COP data is collected in a series of 10 30-sec trials standing on the force plate. Anteroposterior (AP) displacement is measured in cm. A higher number indicates more postural sway.

Postural sway during quiet stance will be assessed from Center-of-Pressure (COP) trajectory data collected at 100 Hz using an Advanced Mechanical Technology Incorporated (AMTI) AccuSway biomechanics force platform at baseline, 4-months, and 12-months. Participants stand on the force platform barefoot in an upright stance with arms relaxed comfortably at their sides, eyes open, feet abducted 10 degrees, and heels separated medio-laterally by 6 cm. COP data is collected in a series of 10 30-sec trials standing on the force plate. Mediolateral (ML) displacement is measured in cm. A higher number indicates more postural sway.

Falls will be defined as an event whereby an individual unexpectedly comes to rest on the ground or another lower level. Participants will be provided monthly fall calendars and asked to mark any falls that occur on the calendar. Completion of monthly fall calendars will be monitored via monthly phone calls and collected at the 4- and 12-month visits. The number of total falls per participant over the entire 12-month follow-up period will be used in analysis.