The physiology of getting older as an athlete is better documented than most people assume, and less bleak. Tanaka and Seals, reviewing decades of endurance data, found peak performance holds until roughly age 35, declines modestly through 50 to 60, then falls progressively faster — driven mainly by declining VO2max, with lactate threshold contributing secondarily. Exercise economy, notably, does not decline at all in trained adults. The Baltimore Longitudinal Study of Aging, tracking peak treadmill VO2 in 810 adults over a median of nearly eight years, put numbers on the curve: 3 to 6 percent per decade in the twenties and thirties, accelerating past 20 percent per decade after seventy.
The more interesting finding is what does not happen. Wroblewski and colleagues studied 40 masters athletes aged 41 to 81 who trained four or five times a week and found that mid-thigh muscle area, quadriceps area and quadriceps peak torque did not decline with age at all, despite rising body fat percentage. Much of what gets attributed to aging muscle appears to be disuse. Both reviews also note that a large share of the endurance decline is mediated by reductions in training volume and intensity an athlete can sustain, not by age directly. Boulder is an unusually good place to test that, and here are seven places where people over 40 are actively doing so.
Boulder Aquatic Masters
Boulder Aquatic Masters is a 501(c)(3) nonprofit that describes itself as celebrating more than thirty years serving the Boulder and Colorado swimming communities, open to adults 18 and up at all levels. Coached workouts run morning, noon and night year-round, with Tuesday and Thursday open-water swims at Boulder Reservoir through the summer; the 2026 open-water season ran from late May to the end of August, and the Reservoir is closed to the club for fall and winter. Pricing is published rather than quoted: $16.50 drop-in, $154 for a ten-swim pass, $137.50 monthly, $577.50 for six months. Swimmers 65 and over, or with Medicare or Medicaid, get a 20 percent discount, and the club says swimmers on a Premium-level Renew Active plan may be able to swim at no additional cost. The first pool workout costs nothing.
Boulder Road Runners
Founded in 1979, with dues of $35 a year, Boulder Road Runners has a deep masters racing structure. Sunday group runs leave from the East Boulder Community Center at 5660 Sioux Drive at 8am from June through September and 9am from October through May. The club fields dedicated masters squads at Women’s 50+, Men’s 50+, Men’s 60+, Women’s 60+ and Men’s 70+ — the Men’s 60+ squad took gold in the USATF Masters National Grand Prix Series in 2017 and 2019, and silver in 2018. Six club runners competed at the 2024 World Masters Athletics Championships in Gothenburg, where club athletes brought home six medals between them, several of them in cross country and the half marathon rather than on the track. It also hosts the All-Comers Summer Track Series at CU’s Potts Field, now in its fourth decade, at $12 an event for members.
LOCO Swimming, Longmont
The county’s other masters swim option. LOCO Swimming runs as a City of Longmont Recreation program with no dues and no US Masters Swimming requirement for morning or midday sessions — you pay facility admission and swim. The schedule puts Monday, Wednesday and Friday 6am and Saturday 7am at Centennial Pool on Alpine Rd, and Tuesday and Thursday noon at the Longmont Rec Center on Quail Rd, moving outdoors to Sunset Pool in summer. Head coach Becky Dreasher has coached Longmont masters since 2014 and holds USMS Level 3 certification. Beginning and Intermediate Masters classes run in seven- and eight-week sessions.
Boulder Tri Club
Boulder Tri Club is a registered USA Triathlon club with membership at $50 a year, drawing members from Boulder plus Louisville, Longmont, Broomfield, Golden, Arvada and Westminster. This is the age-group structure most masters triathletes actually train inside: weekly group rides and runs, training sessions and seminars, club meetings with guest speakers, pasta rides and an annual social. Member benefits include discounts at local bike and multisport shops and at area fitness clubs, and a tie-up with Boulder Aquatic Masters, which BAM publishes on its own membership page as 10 percent off Boulder Tri Club membership plus a thirty-day trial for its swimmers.
Fast Talk Laboratories
If the research says training volume and intensity mediate the decline, the obvious follow-up is knowing what your intensities actually are. Fast Talk Laboratories runs a physiology lab at 1405 Arapahoe Avenue offering in-person VO2max, lactate and metabolic testing, administered by Jared Berg, RD, an exercise physiologist and sports dietitian with more than a decade testing athletes locally. Testing uses a Parvo Medics TrueOne 2400 metabolic cart with a Wahoo KICKR Core in the office for cyclists and off-site treadmill equipment for runners; a session runs 30 to 45 minutes, identifies LT1 and LT2 thresholds and fuel utilisation, and includes same-day interpretation. The lab also sells race-day nutrition plans and consultations.
D3 Multisport
D3 Multisport has coached out of Boulder since 2000, founded by Mike Ricci and now in its twenty-sixth year. Ricci is a USA Triathlon Elite Level 3 coach — the highest US triathlon certification, held by only 22 coaches — plus TrainingPeaks Level 2 and Ironman University certified, and a USAT Coach of the Year. He wrote training plans for Team USA and coached CU’s triathlon team to four consecutive collegiate national titles from 2009 to 2013. The practice’s stated specialties map almost exactly onto the masters athlete: athletes with real time constraints, athletes moving from short to long course, and athletes with large goals regardless of current speed.
CU Sports Medicine and Performance Center
Masters training and injury management are the same subject after a while. CU Sports Medicine and Performance Center occupies the second floor of the Champions Center at 2150 Stadium Drive on the CU Boulder campus, formed in 2015 as a joint venture between staff from the former Boulder Center for Sports Medicine and the CU School of Medicine. Orthopedic surgery, non-operative sports medicine, hip preservation, physical medicine and rehabilitation, advanced imaging, physical therapy and sports performance all sit under one roof, which matters when an overuse injury needs imaging and rehab in the same week. Hours run to 7pm four days a week and Saturday mornings.
Why the scene is this deep here
Some of it is self-selecting: people who care about training at 55 move to places where training at 55 is normal. But there is a research thread too. The definitive review of masters athlete physiology cited at the top of this article was co-authored by Douglas Seals, who runs CU Boulder’s Integrative Physiology of Aging Laboratory, which studies vascular aging and interventions aimed at extending healthspan rather than lifespan. And Boulder Road Runners maintains the Colorado Masters Records database, documenting 47 years of over-30 track competition in the state, from 1979 to 2026, more than 6,000 athlete times across some 275 meets — a concrete measure of the scene’s depth rather than an assertion about it.
Where to start if you are new to this
Low-cost entry points are the two swim programs, since a first Boulder Aquatic Masters workout is free and LOCO asks only for pool admission. If you already train and want to know whether you are training in the right places, physiological testing costs less than a season of guessing. And if you are returning to competition after a decade away, the Wroblewski finding is the one to hold onto: the muscle loss most people assume is inevitable showed up as disuse rather than age in athletes who kept training four or five times a week. That is not a promise about your knees. It is a reason to start.
Featured image: “Lane Lines 2” by brianc — CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/). Source: https://www.flickr.com/photos/51035606497@N01/4679568335
