Lower-limb fitness predicts arterial shear in aging commercial diver fishermen: a detailed look at vascular health, strength and screening opportunities

Table of Contents

1. Key Highlights:
2. Introduction
3. Who are commercial diver fishermen and why their physiology matters
4. Study design and what was measured
5. Vascular structure and stiffness: similar profiles despite two-decade age gap
6. Muscle strength and functional capacity: clear age-related decline
7. Shear rate links lower-limb functional performance to arterial hemodynamics
8. Why handgrip strength did not predict shear rate
9. Body composition and lifestyle: similar but not reassuring
10. Occupational implications: screening, prevention and realistic interventions
11. Interpreting shear rate changes: why they matter for vascular health
12. Limitations that frame interpretation and planning
13. Research and practice priorities going forward
14. Practical recommendations for divers, employers and clinicians
15. Final reflections on occupational health and preventive potential
16. FAQ

Key Highlights:

• Middle-aged and older commercial diver fishermen showed similar vascular structure and stiffness measures, but middle-aged divers had substantially better upper- and lower-limb physical fitness.
• Lower-limb performance on the Ruffier test correlated strongly with arterial shear rate in both the brachial and common carotid arteries, independently of age and blood pressure.
• Pulse wave velocity values above 10 m·s−1 in both groups indicate elevated arterial stiffness and cardiovascular risk, pointing to the need for targeted workplace screening and fitness interventions.

Introduction

Commercial diving for shellfish and mollusks is a physically demanding occupation that often spans decades. This work keeps divers active well into older ages, yet it exposes them to unique physiological stresses: repeated pressure changes, intermittent heavy upper-limb activity at depth, and long periods where buoyancy reduces load on the skeleton and lower limbs. A pilot study of 22 Chilean diver fishermen compared middle-aged (mean 48 years) and older (mean 66 years) workers to characterize vascular status, body composition, lifestyle and physical fitness. The study reveals a striking pattern: despite broadly similar vascular measures and body composition across age groups, older divers show clear declines in muscle strength and lower-limb functional capacity. Those declines, measured with a simple field test, map onto hemodynamic markers—specifically arterial shear rate—in both peripheral and central arteries. The findings suggest both a practical screening route for cardiovascular health in this population and an actionable target for workplace prevention: improving lower-limb functional fitness.

The analysis that follows unpacks the study design, details the key vascular and fitness metrics, interprets the clinical and occupational implications, and outlines practical responses that employers, health services and divers themselves can adopt.

Who are commercial diver fishermen and why their physiology matters

Commercial diver fishermen—commonly called shellfish or mollusk divers in Chile—perform prolonged underwater harvesting at depths that often reach 20–36 meters. Their daily work emphasizes repetitive upper-limb activity (collecting and handling catch) while buoyancy reduces load on the lower limbs and skeleton. That occupational profile creates two competing physiological influences:

• Hyperbaric exposures and repeated deep dives can impair endothelial function, increase oxidative stress and alter arterial hemodynamics, especially after successive deep exposures.
• Sustained muscular work—if present—promotes muscle mass and strength and can protect vascular health and bone density.

Diver fishermen therefore occupy a mixed-risk niche. National surveillance in Chile has flagged high rates of musculoskeletal disorders, hypertension and overweight among divers. SUSESO (the Chilean Superintendence of Social Security) estimated that roughly one-third of divers smoke and that nearly 87% present overweight or obesity—factors that further increase cardiovascular risk. The demographic reality that many divers continue working past 60 years of age makes understanding age-associated vascular and musculoskeletal changes in this occupational group especially important.

Study design and what was measured

Researchers recruited 22 active male diver fishermen from southern Chile and grouped them into middle-aged (MA-DF, n = 11; mean age 48.0 ± 8.5 years) and older adult (OA-DF, n = 11; mean age 66.0 ± 5.9 years). The investigation combined vascular ultrasound, arterial stiffness testing, body composition by dual-energy X-ray absorptiometry (iDXA), standardized fitness tests and lifestyle questionnaires. Key measurements included:

• Brachial artery (BA) and common carotid artery (CCA) diameter and Doppler flow velocities: peak systolic velocity (PSV), end-diastolic velocity (EDV). From these values shear rate (SR), resistivity index (RI), pulsatility index (PI) and Reynolds number (Re) were computed.
• Pulse wave velocity (PWV) and augmentation index measured by validated oscillometric devices; PWV >10 m·s−1 used as a clinical threshold for elevated arterial stiffness.
• Carotid intima–media thickness average and maximum (cIMTavg, cIMTmax).
• Handgrip strength (HGS) for right and left hands using a Jamar dynamometer; average HGS (HGSAV) used in analyses.
• Ruffier–Dickson test for lower-limb functional fitness: heart rate responses and number of squat repetitions in 45 seconds used to compute the Ruffier index and capture squat repetitions as a simple measure of lower-limb functional capacity.
• Full-body and segmental body composition by iDXA: percent body fat, fat-free mass (FFM), and bone mineral content (BMC) for arms, legs and trunk.
• Lifestyle: physical activity using GPAQ, sedentary time and smoking status.

Analytical approach combined group comparisons and multivariable linear regression models adjusted for age and mean arterial pressure (MAP) to probe associations between vascular outcomes (structure and function) and fitness markers (HGSAV and Ruffier test repetitions).

Vascular structure and stiffness: similar profiles despite two-decade age gap

Comparing the two groups revealed no statistically significant differences in most vascular structural and flow parameters. Specific observations include:

• Brachial artery diameter (DBA), PSVBA, EDVBA, shear rate (SRBA), RI, PI and Reynolds number did not differ significantly between MA-DF and OA-DF.
• Common carotid artery diameter (DCCA), PSVCCA, EDVCCA and derived indices (SRCCA, RICCA, PICCA, ReCCA) also showed no significant group differences.
• Carotid intima–media thickness (cIMTavg and cIMTmax), ankle–brachial index (ABI), augmentation index (AIxBA) and pulse wave velocity (PWV) did not differ between groups.

Two clinically relevant points emerge from these results. First, the absence of clear structural differences across a roughly 18-year mean age gap suggests some preservation of vascular structure in elder divers who remain occupationally active. Second, PWV values in both groups averaged above 10 m·s−1, a threshold commonly used to flag elevated arterial stiffness and higher cardiovascular disease (CVD) risk. An elevated PWV across both groups signals that, even though older divers do not present worse vascular measures than younger counterparts in this small sample, overall arterial stiffness may be an occupational-health concern for the cohort as a whole.

Taken together, these data support a nuanced interpretation: occupational activity may help preserve some vascular parameters across age, but baseline arterial stiffness and other risk factors remain a pressing issue requiring intervention.

Muscle strength and functional capacity: clear age-related decline

Physical fitness diverged markedly between groups:

• Handgrip strength: right-hand mean 48.1 ± 6.2 kg (MA-DF) vs 39.8 ± 6.4 kg (OA-DF), p = 0.029. Left-hand mean 46.7 ± 5.9 kg vs 39.5 ± 6.3 kg, p = 0.042.
• Ruffier squat repetitions (45 s): MA-DF averaged 23.2 ± 5.3 repetitions, whereas OA-DF performed 15.5 ± 2.4 repetitions, p = 0.0006.

Despite similar physical activity self-reports across groups (total minutes per week of vigorous, moderate and light activity and sedentary time did not differ significantly), objective measures of muscle strength and lower-limb functional capacity were lower in older divers. That pattern aligns with well-established age-related sarcopenic trends: muscle strength and power decline faster than body mass alone would suggest. The occupational environment—a setting where upper-limb repetitive tasks dominate while buoyancy reduces lower-limb loading—likely compounds lower-limb functional loss with age.

Real-world relevance: older divers who remain active at sea may mask declines in leg function because routine tasks emphasize arm use; nevertheless, lower-limb deficits undermine balance, recovery after strenuous work and long-term mobility. The difference in Ruffier repetitions—more than seven repetitions on average—translates into measurable declines in functional capacity with potential implications for fall risk and capacity to perform rescue or emergency tasks.

Shear rate links lower-limb functional performance to arterial hemodynamics

The study’s most striking finding concerns the association between lower-limb functional capacity and arterial shear rate. In multivariable regression models adjusted for age and MAP:

• Ruffier test repetitions were strongly and positively associated with brachial artery shear rate (SRBA): B = 88.7 s−1 per repetition, p = 0.003 (95% CI: 35.8 to 141.9).
• Ruffier test repetitions were also positively associated with common carotid artery shear rate (SRCCA): B = 38.7 s−1 per repetition, p = 0.042 (95% CI: 1.5 to 75.8).
• Average handgrip strength (HGSAV) did not show significant associations with shear rates in BA or CCA.

Physiological interpretation: shear rate represents the velocity gradient of blood flow along the vessel wall and is a major determinant of endothelial shear stress. Higher shear rates during rest are typically associated with healthier endothelial function and nitric oxide bioavailability. Lower-limb muscular activity engages a large mass of muscle and provokes systemic circulatory adjustments—enhancing venous return, increasing cardiac output during activity and promoting favorable flow patterns. The Ruffier squat test captures a brief but intense activation of large lower-limb muscle groups; better performance likely reflects superior muscular oxidative capacity and cardiovascular responsiveness. The observed correlations indicate that greater lower-limb fitness corresponds with more favorable central and peripheral flow dynamics even at rest.

Clinical implication: a simple, inexpensive field test—Ruffier squat repetitions—may provide insight into vascular flow characteristics that usually require Doppler ultrasound to measure. That opens possibilities for initial workplace screening and targeted referrals.

Why handgrip strength did not predict shear rate

Handgrip strength remains a robust marker of global muscle strength and a predictor of morbidity and mortality in many cohorts. Yet in this study HGSAV was not associated with BA or CCA shear rates. Several plausible explanations exist:

• Handgrip tests target relatively small upper-limb muscles. Their hemodynamic footprint is more regional than systemic when compared with large lower-limb exercises that recruit greater muscle mass and induce larger circulatory responses.
• The occupational tasks of divers emphasize upper-limb endurance and repetitive patterns; such adaptation might preserve HGS but not translate into systemic hemodynamic changes observable at rest.
• The sample size limits statistical power to detect modest associations.

Taken together, the data suggest lower-limb fitness, not upper-limb strength, is the more relevant functional correlate of arterial flow dynamics in this occupational cohort.

Body composition and lifestyle: similar but not reassuring

Precision body-composition measures by iDXA revealed no statistically significant differences across groups in percent body fat, fat-free mass or bone mineral content—either regionally or in total. Nevertheless, trends included slightly higher body fat percentages and marginally lower FFM and BMC among older divers. Segmental analysis suggested a near-significant reduction in leg BMC for older divers (p = 0.088), which could be meaningful for mobility and fracture risk if confirmed in larger samples.

Lifestyle self-reports using GPAQ indicated no significant differences in weekly moderate-to-vigorous physical activity or sedentary time between groups. That finding underscores the limitations of self-reported activity measures in detecting differences in exercise type and mechanical loading. Two groups reporting similar overall activity can nonetheless diverge in the nature of activity (for example, upper-body dominated occupational work vs structured resistance or weight-bearing training).

Public-health context from prior reporting: SUSESO data place this workforce at elevated risk—high prevalence of overweight/obesity and a substantive smoking rate. Those factors, combined with PWV levels above the clinical threshold, argue for workplace-focused cardiovascular risk reduction strategies.

Occupational implications: screening, prevention and realistic interventions

The study highlights several actionable routes for improving diver health:

1. Screening with field tests that inform vascular risk
   • Ruffier squat performance correlated with arterial shear rate. Worksite health programs could adopt the Ruffier test or comparable 45-second squat tests for routine screening. Divers who perform poorly would be prioritized for Doppler assessment (shear rate, cIMT) and arterial stiffness testing (PWV).
   • HGS remains useful as a sarcopenia marker; incorporate it into broader surveillance but prioritize lower-limb evaluations for vascular relevance.
2. Strength and functional training as a health intervention
   • Resistance training, particularly exercises that load the legs (squats, step-ups, deadlifts) improves muscle mass, bone density and functional capacity. Trials in older adults show measurable gains in Ruffier-like performance after relatively short interventions (e.g., 6 weeks).
   • For divers, training plans must account for schedules, diving safety considerations and access to equipment. Short, frequent sessions—"exercise snacks" or brief high-intensity resistance sets—can be practical. (A randomized trial in older adults showed that intermittent endurance training reduces PWV; short resistance programs produce clinically meaningful increases in muscle size.)
3. Targeted cardiovascular risk reduction
   • Given PWV >10 m·s−1 in both groups, immediate attention to blood pressure control, weight management, tobacco cessation and aerobic conditioning is warranted. Exercise prescriptions that combine aerobic and resistance elements reduce arterial stiffness and improve endothelial function.
   • Occupational health services should screen for hypertension and support medical management alongside exercise programs.
4. Policy and workplace implementation
   • Divers are a hard-to-reach occupational group. Health interventions should be coordinated with divers’ organizations and the maritime authority to align with work cycles and ensure access. Preventive programs become sustainable when integrated into obligatory or incentivized medical surveillance offered by employers or social security systems.
   • Practical steps include periodic on-site screenings (Ruffier, HGS, blood pressure), referral pathways for vascular imaging when indicated, and training modules adaptable to remote coastal communities.

Real-world example: an employer in a coastal fishing community could implement quarterly screenings. Divers performing fewer than a pre-specified number of Ruffier repetitions—set relative to age- and sex-matched norms—would be offered a six-week supervised leg-focused strength program and re-tested for both functional gains and, when available, PWV reduction.

Interpreting shear rate changes: why they matter for vascular health

Shear rate is a surrogate for endothelial shear stress, a biomechanical signal that regulates the endothelial release of nitric oxide and other vasoactive substances. Sustained low or oscillatory shear stress favors endothelial dysfunction and atherogenic signaling; steady, higher laminar shear stress supports anti-inflammatory and vasoprotective pathways. The association between better Ruffier performance and higher resting shear rates suggests that habitual capacity for rapid lower-limb muscular activation supports more favorable flow patterns even at rest. That has two implications:

• Functional capacity is not an isolated muscular trait; it reflects cardio-circulatory conditioning that influences arterial biology.
• Interventions that enhance leg muscle capacity and functional power may shift shear patterns towards protective states and thus translate to vascular benefit beyond muscular advantages.

Linking field tests to endothelial markers transforms workplace fitness from a performance target into a vascular-health intervention.

Limitations that frame interpretation and planning

The study is a pilot and offers preliminary, hypothesis-generating evidence rather than conclusive proof. Important limitations include:

• Small sample size (n = 22) and voluntary recruitment limit generalizability and raise possible selection bias.
• Cross-sectional design prevents causal inference (better Ruffier performance could reflect healthier vasculature rather than cause it).
• Manual measurement of heart rate during the Ruffier protocol introduces variability; future studies should use heart-rate monitors for greater precision.
• Seasonal and environmental diving variables (number of dives, depth exposure patterns, water temperature) were not quantified; these factors could influence vascular measures.
• The cohort included only male diver fishermen from southern Chile. Broader demographic representation, including women and divers from other regions, would strengthen external validity.

Despite these limits, the combination of gold-standard iDXA body composition, vascular imaging and practical fitness measures is a notable strength. The findings justify larger longitudinal studies and pilot interventional trials in the occupational setting.

Research and practice priorities going forward

To translate these findings into improved diver health, research and practice should focus on:

• Larger, longitudinal cohort studies in diverse diving populations to determine whether changes in lower-limb fitness predict future vascular change or CVD events.
• Randomized workplace trials testing leg-focused resistance training programs for their effects on Ruffier scores, shear rate, PWV and clinical outcomes.
• Implementation research to design feasible screening and training programs adapted to the rhythms and constraints of commercial diving (e.g., modular exercises that require minimal equipment and short time commitments).
• Integration of diving-specific exposure metrics (hours underwater, decompression profiles, repetitive deep exposures) to parse how hyperbaric stress interacts with fitness to affect vascular health.
• Cost-effectiveness analyses to prioritize interventions in resource-constrained coastal communities.

The evidence supports a pragmatic hypothesis: improving lower-limb functional capacity in diver fishermen will lead to measurable improvements in arterial flow patterns and, potentially, reduced long-term cardiovascular risk.

Practical recommendations for divers, employers and clinicians

For occupational health teams and clinicians who assess or manage diver fishermen, the study suggests immediate, low-cost steps:

• Incorporate the Ruffier squat test (45 s) and handgrip dynamometry into routine medical surveillance. These tests are quick, portable and informative.
• Flag divers with poor Ruffier performance for further vascular evaluation, especially if blood pressure is elevated or other risk factors (smoking, obesity) are present.
• Prescribe leg-focused resistance training for older divers and those with low Ruffier scores. Programs can begin with bodyweight squats, step-ups and progressive loading over 6–12 weeks. Supervision and education reduce injury risk and improve adherence.
• Address traditional cardiovascular risk factors: measure and manage blood pressure, promote tobacco cessation and dietary support for weight control.
• Coordinate interventions with diving schedules and local leaders to ensure access, uptake and cultural fit.

Employers will find that brief, targeted programs can be integrated into shore-based time and will yield benefits in worker safety, functional capacity and potentially reduced medical costs.

Final reflections on occupational health and preventive potential

Diver fishermen sit at the intersection of occupational exposure and aging physiology. This pilot study shows that a simple, repeatable test of lower-limb function maps onto arterial hemodynamics that are otherwise only measurable with ultrasound. That linkage creates an opening for large-scale, low-cost screening and for targeted, feasible interventions that address both functional decline and vascular risk. While more definitive trials are required, the pragmatic message for coastal communities is clear: assessing and strengthening leg function offers a direct route to better vascular health in a workforce that remains active into older age yet faces elevated background CVD risk.

FAQ

Q: What is arterial shear rate and why is it important? A: Arterial shear rate is a measure of how rapidly blood velocity changes across the vessel lumen near the wall. It serves as a proxy for endothelial shear stress, a mechanical stimulus that governs endothelial function. Higher, steady shear rates tend to promote nitric oxide release, vasodilation and anti-inflammatory signaling, while low or oscillatory shear is associated with endothelial dysfunction and atherosclerosis. In this study, higher shear rates in the brachial and carotid arteries were associated with better lower-limb functional performance.

Q: What exactly is the Ruffier test and how was it used? A: The Ruffier–Dickson test evaluates cardiovascular response and functional capacity using heart rates measured before, immediately after and one minute after a 45-second squat test. In this study, the number of squat repetitions during the 45-second interval was also recorded and used as a practical index of lower-limb functional capacity. That repetition count showed the strongest association with arterial shear rates.

Q: How large were the differences in strength and functional capacity between middle-aged and older divers? A: Middle-aged divers had higher handgrip strength by approximately 8–9 kg in both hands. For the Ruffier squat repetitions, middle-aged divers averaged 23.2 repetitions versus 15.5 in older divers—a difference of about 7.7 repetitions, statistically highly significant.

Q: Why didn’t handgrip strength predict arterial shear rates? A: Handgrip strength targets smaller upper-limb muscles and may reflect regional muscular capacity rather than systemic cardiovascular conditioning. Lower-limb exercises recruit much larger muscle mass and provoke greater systemic hemodynamic responses; therefore, lower-limb fitness is more likely to influence central blood flow and shear patterns transferable to larger arteries.

Q: What does PWV >10 m·s−1 mean for these divers? A: Pulse wave velocity quantifies arterial stiffness. Values above 10 m·s−1 are commonly used to indicate elevated arterial stiffness and higher cardiovascular risk. Both groups in the study averaged PWV above this threshold, signaling that arterial stiffness—and corresponding cardiovascular risk—may be a concern across the diver population studied.

Q: Can a simple exercise program change shear rates or PWV? A: Controlled trials in non-diver populations have shown that short-term aerobic and resistance programs can reduce PWV and improve endothelial function. The magnitude and timing of change depend on baseline health, program intensity and duration. The pilot data here justify trials to test whether strengthening lower-limb capacity in divers reduces arterial stiffness and improves shear metrics.

Q: Should diver health surveillance change based on this study? A: The findings support adding simple functional tests—Ruffier squat repetitions and handgrip strength—to routine surveillance, and using poor performance as a trigger for more detailed vascular assessment and targeted training interventions. Surveillance should also continue to include blood pressure, weight, smoking status and, where feasible, PWV screening.

Q: Are the results definitive and applicable everywhere? A: No. This is a small pilot study of male divers in southern Chile. Results are hypothesis-generating and indicate directions for intervention and larger studies. Generalization to other diving populations, including recreational divers, women, or divers with different exposure patterns, will require further research.

Q: How should diving organizations implement practical fitness programs? A: Start with low-cost, short-duration programs focused on leg strength and functional tasks—bodyweight squats, step-ups, lunges and progressive resistance exercises. Programs should be scheduled during non-diving periods, supervised initially to ensure safe technique, and followed by re-assessment with Ruffier and HGS. Coordination with local health services and worker representatives enhances uptake.

Q: What are the next research steps? A: Larger, prospective studies should test whether improving lower-limb function causes favorable changes in shear rate and PWV, and whether those vascular changes translate into lower incidence of clinically important cardiovascular events. Interventional trials adapted to the practical constraints of diving work are a priority.