Four Weeks In. Still Rowing.

Team Nautilus are now four weeks into their 2,000-mile row around Great Britain. The challenge is no longer a shock to the system — it has become the system. Two hours on. Two hours off. Day after day, mile after mile.

The Week Four data tells a story of a crew operating in a sustained ultra-endurance state. Strain remains extremely high. Energy demands are enormous. And for some crew members, the body is beginning to show the physiological signs of prolonged deficit.

This is Week Four.

A Note on This Week's Data

As with Week Three, sleep and recovery metrics — including recovery score, HRV and resting heart rate — remain unavailable due to limitations in data collection while at sea. This week's report focuses on workload, strain and energy expenditure.

Week Four Key Findings (June 23rd – June 29th)

Strain

Average daily strain across the crew was 18.0 — a slight reduction of 3.7% on Week Three, but still firmly in the WHOOP "All Out" category (18–21). This is not a sign of reduced effort. It reflects the body operating at the upper limit of sustainable output, week after week.

Several crew members continued to record strain scores of 20+ — among the highest values on the scale — consistent with elite ultra-endurance rowing demands.

Energy Expenditure

Average calories burned dropped to 2,616 kcal per day — down 13.4% on Week Three. Individual expenditure ranged significantly across the crew, reflecting differences in shift patterns, body mass and rowing output.

This reduction in average calorie burn, combined with sustained high strain, raises an important question: are the crew fuelling enough to match what they are putting out?

Workout Volume

Average recorded workouts fell to 26.3 per week — down 19.6% — though this reflects fewer sessions rather than lower intensity. Those who did row, rowed hard.

The Bigger Picture: Energy Balance at Sea

At Week Four, our performance team has identified energy balance as the primary focus for the remainder of the expedition.

In ultra-endurance settings like the GB Row Challenge, it is common — and expected — for crew members to enter a state of negative energy balance. When calorie output consistently exceeds calorie intake, the body begins to draw on stored energy reserves. At a deficit of 500–1,000 kcal per day, a crew member may lose approximately 0.5–1.0 kg of body mass per week. In the short term, this is a normal physiological response to prolonged endurance work.

Over time, however, sustained energy deficit carries real performance risks:

• Reduced power output during high-intensity rowing efforts
• Slower recovery between shifts
• Increased perception of fatigue across the day
• Greater reliance on fat as a fuel source, reducing the ability to sustain peak effort

Managing this is not simply a matter of eating more. At sea, appetite suppression under high physiological load is common. The challenge is maintaining consistent, structured fuelling even when hunger signals are absent — because by the time fatigue sets in, the deficit has already compounded.

Individual Highlights

• Highest strain this week: 20.7 daily average — up 15.6% on the previous week — despite completing fewer sessions. Each effort is now costing more.
• Highest energy output: 3,154 kcal/day, alongside 40 recorded workouts — the highest session count in the crew this week — reflecting back-to-back effort cycles with minimal gaps.
• Notable variation: Two crew members recorded significantly reduced workloads this week, with one individual logging just 6 sessions (down 78.6%) and a strain score of 9.9. Whether due to illness, injury or planned rest, the body's response to lower load in an ultra-endurance environment still requires careful nutritional management to stay ready for the next high-demand block.

Week Four Focus: Fuelling the Final Miles

With the crew now deep into the expedition, the performance priorities are clear:

• Maintain consistent energy intake aligned to daily expenditure — even when appetite is suppressed.
• Prioritise carbohydrate availability before, during and between every rowing shift to sustain power output and delay fatigue.
• Avoid prolonged low-fuel gaps across the 2-hours-on/2-hours-off cycle. The body cannot afford to be underfuelled heading into a shift.
• Refuel rapidly after every session — carbohydrate-focused recovery intake in the first 30 minutes after a shift is one of the most impactful interventions available at sea.
• Stay on top of hydration and electrolytes regardless of workload level. Even reduced-output days carry a significant fluid demand in the expedition environment.

Follow the PEAK4 x Team Nautilus performance tracker for weekly updates throughout the GB Row Challenge 2026. The crew continue their circumnavigation of Great Britain — fuelling hard, resting smart and rowing on.