Swim Fitness Training Plan: Weekly Ratios for Aerobic Endurance, Anaerobic Threshold, and Speed Workouts

Introduction

One of the core challenges in swim training is “what intensity should I train at today?” Too many beginner and intermediate swimmers only have two training modes: easy slow swimming, or all-out sprinting. Neither extreme effectively improves swimming fitness—the former provides insufficient stimulus, while the latter causes excessive fatigue.

Scientific swim fitness training requires consciously distributing training volume across three intensity domains: Aerobic Endurance, Anaerobic Threshold, and Speed/Power. Each of these three domains offers distinct physiological benefits, and all are indispensable.

Physiological Benefits of the Three Intensity Domains

Aerobic Endurance Training (Z1–Z2, approximately 60–75% max heart rate)

The physiological benefits of aerobic endurance training include:

• Increasing the volume of blood pumped per heartbeat (stroke volume), improving cardiac efficiency
• Increasing capillary density in muscles, improving oxygen delivery
• Enhancing fat metabolism ratio, extending endurance performance duration
• Accelerating lactate clearance rate, improving sustained capacity at higher intensities

Characteristics: Benefits are slow to accrue but long-lasting, forming the foundation for all other training. Swimmers with too low a proportion of this training will struggle to maintain quality in higher-intensity sessions.

Anaerobic Threshold Training (Z3–Z4, approximately 75–90% max heart rate)

The physiological benefits of anaerobic threshold training include:

• Raising lactate threshold speed (i.e., the fastest speed maintainable before lactate begins to accumulate significantly)
• Increasing the activity of muscle lactate-clearing enzymes
• Improving the ability to sustain an “uncomfortable but controllable” pace
• Providing the most direct benefit to race-pace improvement

Characteristics: Training benefits appear quickly, but require longer recovery time (24–48 hours). Should not exceed 2 sessions per week.

Speed Training (Z5–Z6, approximately 90%+ max heart rate)

The physiological benefits of speed training include:

• Increasing maximum stroke rate and muscular power
• Improving neuromuscular coordination, making movements more automatic at high swimming speeds
• Enhancing muscle fiber recruitment capacity, particularly the activation of fast-twitch fibers
• Improving race-start and sprint-segment capabilities

Characteristics: Training volume is small, but the impact on race performance is significant. Each session’s volume should not exceed 10–15% of total volume.

Recommended Ratios by Swimmer Level

Important note: These ratios are for the “maintenance/base-building” phase of training. During the “peak phase” 4–6 weeks before a race, the proportion of threshold and speed training can be temporarily increased to 30–35%.

Sample Weekly Training Plan (Intermediate Swimmer)

Using an intermediate swimmer (3 sessions per week, approximately 12,000m weekly) as an example:

Monday: Aerobic Endurance Day (4000m)

• Warm-up: Mixed swimming 600m (Z1)
• Main set: 1×2500m continuous swimming (Z2, steady pace)
• Supplemental: 6×100m (Z2, set departure intervals)
• Cool-down: 300m breaststroke (Z1)
• Intensity ratio: Aerobic 100%

Wednesday: Threshold Day (3500m)

• Warm-up: Mixed swimming 500m (Z1)
• Activation: 4×100m progressive acceleration (Z2→Z3)
• Main set: 4×500m (Z3–Z4), 90 seconds rest between reps
• Cool-down: 300m easy swimming (Z1)
• Intensity ratio: Aerobic 30%, Threshold 55%, Speed 15%

Saturday: Speed + Mixed Day (4500m)

• Warm-up: 600m mixed swimming
• Technique set: 4×50m high-elbow catch drills
• Speed set: 10×50m Z5 sprints, 60 seconds rest between reps
• Aerobic set: 1×2000m continuous swimming (Z2)
• Cool-down: 300m breaststroke
• Intensity ratio: Aerobic 55%, Threshold 15%, Speed 30%

Seasonal Adjustments

The intensity ratios of swim fitness training should be adjusted according to the training cycle:

Base Phase (16–12 weeks before race)

• Aerobic endurance 80%, threshold 15%, speed 5%
• Focus: Build aerobic foundation, increase training volume

Development Phase (12–6 weeks before race)

• Aerobic endurance 65%, threshold 25%, speed 10%
• Focus: Raise threshold speed, increase training intensity

Peak Phase (6–2 weeks before race)

• Aerobic endurance 55%, threshold 25%, speed 20%
• Focus: Maintain and enhance race-pace feel

Taper Phase (2 weeks before race)

• Training volume reduced to 50%, but maintain frequency of speed training
• Focus: Allow full recovery to arrive at the race in optimal condition

Practical Recommendations

• You don’t need to include all three intensities every week—design a “microcycle” instead: focus on aerobic work one week, threshold work the next, ensuring adequate recovery
• Heart rate recovery after training is an indicator of appropriate intensity: after aerobic training, heart rate should drop below 120bpm within 3 minutes
• Use a swim heart rate watch or ear-clip heart rate monitor to track intensity—perceived effort is often underestimated in the water
• Feeling “too easy” on aerobic endurance days is correct—most people’s aerobic training pace should be 10–15% slower than what they “think” their aerobic pace is

Conclusion

The base of the swimming fitness pyramid is a large volume of solid aerobic endurance training; the middle layer is threshold training that lets you swim faster; the top layer is the speed capacity that lets you break away in races. All three are indispensable, but the foundation is always the most important. Many amateur swimmers in Taiwan rush to pursue speed at the outset, skipping the aerobic foundation, only to see progress stall or even suffer injuries. Patiently building a properly proportioned fitness structure is the correct path to sustained improvement.

Related Reading

• Swimming Dual-Energy System Training: Scientific Weekly Scheduling of Aerobic and Anaerobic Workouts
• Building Your Swimming Aerobic Foundation: Weekly Scheduling and Monitoring of Low-Intensity Swimming
• Building Your Swimming Aerobic Foundation: Setting Weekly Training Volume for Low-Intensity Long-Distance
• 4-Week Anaerobic Interval Strengthening for Swimming: Breaking Through Your Speed Ceiling