Pain in Aging Former Athletes, Master's Athletes, and Nonathletes

The maximum stimulus intensity that the participant can tolerate will be measured by placing a thermode (Q-Sense, Medoc) on the ventral forearm. Three trials will be completed with the baseline temperature set at 35°C that increases at a rate of 1°/s with a maximum temperature of 50°C. Participants will be asked to press a timing device when they can no longer tolerate the temperature (i.e., pain tolerance), and this temperature will be recorded as the maximum stimulus intensity.

Pressure Pain Thresholds (PPTs) will be used to measure group differences in pain sensitivity at baseline and the hypoalgesic response (increase in PPTs) during the exercise sessions with a pressure algometer (Algomed, Medoc) at the exercising limb, contralateral limb, and systemically at the right upper trapezius muscle. Two trials separated by a 10-second interval will be performed at each site with a 1cm^2 rubber tip at a rate of 50 kPA/sec. Participants will be instructed to press a timing device when the pressure first changes to pain (i.e., pain threshold). Practice trials with be performed on the fourth digit fingernail bed prior to formal assessment at quad/trap and order will be randomized. The change scores from pre- to post-strength exercise and from pre- to post-aerobic exercise will be used as the primary outcome in Aim 2.

Physical activity (PA) will be monitored continuously using an activPAL activity monitor. Step counts will be recorded as the average number of steps taken per day.

Total sedentary behavior will be assessed using an activPAL activity monitor and recorded as the average daily amount of time in wakeful sedentary behavior (hours:minutes).

The Patient-Reported Outcomes Measurement Information System (PROMIS) Pain Intensity-SF v.1.0 3a will be collected at baseline to capture average pain and worst pain intensity over the past 7 days and right now. The survey has 3 questions where respondents rates pain from no pain (1) to very severe pain (5). The total raw score ranges from 3 to 15 with higher scores indicating more severe pain.

Pain distribution or location at rest and with movement will be assessed using the Michigan Body Map for Pain (validated questionnaire).

Temporal summation of pain (TSP) is an increase in pain with a repetitive or constant-intensity, noxious stimulus and represents central pain facilitation. A custom-made pressure pain device, used frequently in the assessment of exercise-induced hypoalgesia, will assess TSP and consists of an 8 x 1.5-mm Lucite edge (Romus Inc., Milwaukee, WI) placed on the mid portion of the middle phalanx of the right index finger for 2 min. A 10-N force (equivalent to a 1-kg mass) will be applied to the Lucite edge, and participants will be asked to press a timing device when the pressure first changes to pain (i.e., pain threshold) and to rate the intensity of pain on a 0-10 numerical pain rating scale every 20-s throughout the test. The increase in the pain intensity during the 2-minute test represents TSP.

Condition pain modulation (CPM) is the concept that pain inhibits pain and will be used to indirectly measure the efficiency of descending inhibitory pathways. For the CPM protocol, PPTs (test stimulus) will be measured using a pressure algometer (AlgoMed, Medoc) as described above at the quadriceps and upper trapezius muscles with and without the participant's foot submerged in an ice water bath (conditioning stimulus). An increase in PPTs during the conditioning stimulus represents the pain inhibits pain phenomenon, whereas no change or decrease in PPTs indicates low CPM efficiency.

The numeric pain rating scale (0-10) will be used to assess pain before, during, and after the strength and aerobic exercise interventions.

Prolonged (>1 hours) bouts of sedentary behavior will be assessed using an activPAL activity monitor.

Sleep duration will be monitored remotely throughout the study using an Oura Ring. Sleep duration will be measured in time (hours:minutes) with greater values indicating longer sleep.

Rating of Perceived Exertion (RPE) will be assessed before, during, and after the strength and aerobic exercise interventions. The RPE scale ranges from 6 (no exertion at all) to 20 (maximal exertion) with high values indicating greater exertion.

Participants will complete standardized isometric strength testing on an electromechanical dynamometer using our established protocol. Following submaximal warm-up efforts, participants will complete 5 maximal effort (i.e., 100%) isometric knee extensions (i.e., maximal volitional contractions [MVCs]) with rest breaks (~1 minute) in between. The order of limbs will be randomized unless the participant has any knee or lower extremity pain prior to testing in which case the less involved limb will be tested first. The peak value from the MVC for each limb will be used to determine the target intensity of the moderate-intensity strength exercise intervention.

Participants will perform the submaximal aerobic 3-minute YMCA Step Test using a 12-inch step at a stepping rate of 24 steps/min set via a metronome set to 96 beats/min for each foot movement. Following 3 minutes of stepping, the participant immediately stops, sits down, and remains still. The total one-minute post-exercise heart rate is the participant's score.

A detailed injury and surgical history will be captured by a licensed physical therapist or other trained study personnel using an injury and surgical history questionnaire.

Sleep latency will be monitored remotely throughout the study using an Oura Ring. Sleep latency is the time (in minutes) it takes to fall asleep.

Physical activity (PA) will be monitored continuously using an activPAL activity monitor. Metabolic equivalents of task, an indicator of overall activity level, will be recorded.

Sleep efficiency will be monitored remotely throughout the study using an Oura Ring. Sleep efficiency is the percentage of time in bed spent asleep (0-100%). Higher values indicate greater sleep efficiency, whereas lower values are indicative of restlessness.