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The evaluation of critical speed (Vcrit) in high-performance swimmers is a widely used method to assess aerobic and anaerobic capacities, as well as to establish personalized training zones. Below, I provide a detailed explanation based on the knowledge available to date, including its definition, assessment methods, practical applications, and its relationship with aerobic and anaerobic zones.

What is Critical Speed (Vcrit)?

Critical swimming speed (Vcrit, or CSS for Critical Swimming Speed) is defined as the theoretical maximum speed a swimmer can maintain over an extended period without reaching exhaustion. It is a practical indicator of aerobic capacity and is closely related to the lactate threshold or the maximal lactate steady state (MLSS), though it may slightly overestimate it if not properly adjusted.

Origin: The concept stems from the critical power model developed by Monod and Scherrer (1965) and was adapted to swimming by Wakayoshi et al. (1992). It is based on the linear relationship between the distance swum and the time taken, where the slope of this line represents Vcrit, and the y-intercept reflects the anaerobic reserve capacity.

Physiological Significance: It represents a balance between lactate production and clearance, making it useful for evaluating sustained aerobic performance.

Methods for Assessing Critical Speed

Vcrit is calculated from maximum-intensity swimming tests over different distances. Several protocols exist, but the most common are:

1. Two-Distance Protocol:
   • Typical Distances: 50 m and 400 m, or 200 m and 400 m.
   • Procedure: The swimmer performs both tests at maximum intensity with sufficient rest between them (ideally on separate days to avoid fatigue). The time for each distance is recorded.
   • Calculation: A line is plotted between the points (distance, time), and the slope of this line is the Vcrit (in m/s). For example:
     • Simplified formula: Vcrit = (D2 - D1) / (T2 - T1), where D1 and D2 are the distances (in meters) and T1 and T2 are the times (in seconds).
   • Advantage: Practical and less time-consuming.
   • Limitation: May overestimate Vcrit in sprinters due to a greater anaerobic contribution in short distances.

1. Three- or Four-Distance Protocol:
   • Typical Distances: 50 m, 100 m, 200 m, and 400 m.
   • Procedure: Similar to the previous protocol but with more data points for greater accuracy.
   • Calculation: Linear regression is used to determine the slope (Vcrit) and anaerobic capacity (y-intercept).
   • Advantage: Higher precision and better representation of the aerobic-anaerobic balance.
   • Limitation: Requires more time and effort from the swimmer.

1. Practical Considerations:
   • Warm-Up: Must be standardized (e.g., 800-1200 m of easy swimming plus progressive drills).
   • Conditions: Conduct tests in the same pool, using the same stroke (typically freestyle), and without significant changes in the swimmer’s physical condition.
   • Correction: Some authors, such as Maglischo (2009), suggest adding 2-3 seconds per 100 m to the Vcrit-derived time to align it with the actual lactate threshold and avoid overestimation.

Relationship with Aerobic and Anaerobic Zones

Vcrit serves as a key reference point for delineating aerobic and anaerobic training zones in high-performance swimmers. These zones are established by adjusting the speed based on Vcrit and the swimmer’s individual characteristics (age, sex, specialty). Below are the typical zones:

1. Aerobic Zones:
   • Light Aerobic (Zone 1):
     • Intensity: 70-85% of Vcrit.
     • Purpose: Improves basic aerobic endurance, fat oxidation efficiency, and active recovery.
     • Example: If Vcrit = 1.4 m/s (equivalent to 71.4 s/100 m), the pace would be ~83-90 s/100 m.
   • Moderate Aerobic (Zone 2):
     • Intensity: 85-95% of Vcrit.
     • Purpose: Develops aerobic capacity and muscular endurance.
     • Example: Pace of ~75-80 s/100 m.
   • Intense Aerobic (Zone 3 or Threshold):
     • Intensity: 95-100% of Vcrit (approximately MLSS).
     • Purpose: Enhances aerobic power and lactate tolerance.
     • Example: Pace of ~71-74 s/100 m.
     • Note: This zone typically aligns with the lactate threshold speed (4 mmol/L), though Vcrit may be slightly higher.

1. Anaerobic Zones:
   • Anaerobic Threshold (Zone 4):
     • Intensity: 100-110% of Vcrit.
     • Purpose: Builds lactate tolerance and prepares for medium-duration efforts (200-400 m).
     • Example: Pace of ~65-70 s/100 m.
   • Maximum Anaerobic (Zone 5):
     • Intensity: >110% of Vcrit.
     • Purpose: Develops anaerobic capacity and maximum power (50-100 m).
     • Example: Pace of <65 s/100 m.

• Adjustments: Maglischo (2009) recommends adding 3-6 seconds per 100 m to Vcrit for basic endurance work and adjusting based on specialty (sprinters require higher zones, distance swimmers lower ones).

Applications in High-Performance Swimmers

1. Assessment of Aerobic Capacity:
   • Vcrit shows a high correlation with physiological parameters such as speed at 4 mmol/L lactate (r=0.95) and ventilatory threshold (r=0.82), per studies like Wakayoshi et al. (1992).
   • It allows monitoring of improvements after aerobic training periods (MacLaren and Coulson, 1999).

1. Assessment of Anaerobic Capacity:
   • The y-intercept in the Vcrit calculation represents the anaerobic reserve (distance swimmable using pure anaerobic energy). This is useful for sprinters and short events.

1. Training Programming:
   • Coaches use Vcrit to set specific paces in training sets. For example:
     • Basic endurance: 10x400 m at 90% of Vcrit.
     • Threshold: 6x200 m at 100% of Vcrit with short rests.
     • Anaerobic power: 8x50 m at 120% of Vcrit.

1. Advantages:
   • Non-invasive, cost-effective, and easy to implement (requires only a stopwatch and pool).
   • Applicable to large groups and swimmers of varying levels.

Scientific Evidence and Correlations

• Wakayoshi et al. (1992): Found that Vcrit correlates with VO2 max (r=0.818), speed at the onset of lactate accumulation (r=0.949), and 400 m freestyle performance (r=0.864), validating it as an endurance index.
• Pelayo et al. (2000): Highlighted its utility as a physiological and technical criterion for monitoring performance in competitive swimmers.
• Maglischo (2009): Proposed practical adjustments to align it with the lactate threshold and optimize its use in training.

Limitations

• Overestimation: In tests with short distances (50 m), anaerobic contribution can inflate Vcrit, making it less representative of MLSS.
• Specificity: Vcrit varies by stroke and requires adjustments for styles other than freestyle.
• Fatigue: If tests are not conducted with adequate rest, results may be inaccurate.

Practical Example

Suppose a high-performance swimmer has the following times:

• 200 m: 2:00 (120 s)
• 400 m: 4:10 (250 s)

Vcrit Calculation:

• Vcrit = (400 - 200) / (250 - 120) = 200 / 130 = 1.54 m/s.
• Pace per 100 m = 100 / 1.54 = 64.9 s/100 m.

Training Zones:

• Light Aerobic: ~75-80 s/100 m.
• Intense Aerobic: ~65-68 s/100 m.
• Maximum Anaerobic: <60 s/100 m.

Conclusion

Critical speed assessment is a powerful tool for high-performance swimmers, enabling simple and effective measurement of aerobic and anaerobic capacities. Its primary strength lies in its practical applicability for defining training zones, tracking progress, and personalizing plans based on an athlete’s needs. However, it requires careful execution and specific adjustments to accurately reflect each swimmer’s physiological demands.

Protocols for Evaluating Critical Speed

1. Two-Distance Protocol (200 m and 400 m)  
   • Objective: Assess Vcrit quickly and practically.  
   • Equipment: Pool (25 m or 50 m), stopwatch, coach or assistant.  
   • Procedure:  
     1. Warm-Up: 800-1000 m of easy swimming (e.g., 400 m easy freestyle, 200 m technique, 200 m progressive, 100 m controlled sprint).  
     2. Test 1: 200 m at maximum intensity from a standing start (no dive platform push-off if possible). Record the exact time (e.g., 2:00 minutes = 120 seconds).  
     3. Rest: Minimum 30 minutes (ideally performed on separate days to avoid fatigue).  
     4. Test 2: 400 m at maximum intensity from a standing start. Record the time (e.g., 4:10 minutes = 250 seconds).
   • Calculation:  
     1. Formula: Vcrit = (D2 - D1) / (T2 - T1), where D1 and D2 are distances (m) and T1 and T2 are times (s).  
     2. Example: Vcrit = (400 - 200) / (250 - 120) = 200 / 130 = 1.54 m/s.  
     3. Pace per 100 m: 100 / 1.54 = 64.9 s/100 m.
   • Note: Adjust by +2-3 s/100 m to align with the lactate threshold (real pace ~67-68 s/100 m).

1. Three-Distance Protocol (50 m, 200 m, 400 m)  
   • Objective: Greater precision by including a broader range of efforts.  
   • Equipment: Same as above.  
   • Procedure:  
     1. Warm-Up: 1000 m (e.g., 500 m easy, 300 m technique, 200 m progressive).  
     2. Test 1: 50 m at maximum intensity (e.g., 25 s).  
     3. Rest: 15-20 minutes.  
     4. Test 2: 200 m at maximum intensity (e.g., 120 s).  
     5. Rest: 30-45 minutes (or the next day).  
     6. Test 3: 400 m at maximum intensity (e.g., 250 s).
   • Calculation:  
     1. Use linear regression with points (50, 25), (200, 120), (400, 250).  
     2. Approximate result: Vcrit ≈ 1.55 m/s (slope of the line).  
     3. Pace per 100 m: 100 / 1.55 = 64.5 s/100 m.
   • Advantage: Reduces anaerobic bias from short distances by including more data.

1. Four-Distance Protocol (50 m, 100 m, 200 m, 400 m)  
   • Objective: Maximum precision for specialized swimmers.  
   • Procedure:  
     1. Warm-Up: 1200 m (600 m easy, 400 m technique, 200 m sprint).  
     2. Tests: 50 m (24 s), 100 m (55 s), 200 m (120 s), 400 m (250 s), with rests of 15-45 minutes between tests or on separate days.
   • Calculation:  
     1. Linear regression: Vcrit ≈ 1.56 m/s.  
     2. Pace per 100 m: 100 / 1.56 = 64.1 s/100 m.
   • Note: The y-intercept (~10-15 m) indicates anaerobic reserve.

Practical Examples

Example 1: Middle-Distance Swimmer (200 m - 400 m)  

• Protocol Data (2 distances):  
  • 200 m: 2:00 (120 s).  
  • 400 m: 4:10 (250 s).
• Calculation:  
  • Vcrit = (400 - 200) / (250 - 120) = 1.54 m/s.  
  • Pace per 100 m = 64.9 s/100 m.  
  • Threshold adjustment: ~67 s/100 m (+2 s).

Training Zones:  

1. Light Aerobic (Z1): 75-80 s/100 m.  
   • Set: 12x100 m at 1:18 with 15 s rest.

1. Moderate Aerobic (Z2): 70-75 s/100 m.  
   • Set: 8x200 m at 2:22 with 20 s rest.

1. Intense Aerobic (Z3): 67-70 s/100 m.  
   • Set: 6x300 m at 3:27 with 30 s rest.

1. Anaerobic Threshold (Z4): 62-65 s/100 m.  
   • Set: 10x50 m at 32 s with 1:00 rest.

1. Maximum Anaerobic (Z5): <62 s/100 m.  
   • Set: 6x50 m at 30 s with 2:00 rest.

Example 2: Sprint Swimmer (50 m - 100 m)  

• Protocol Data (3 distances):  
  1. 50 m: 24 s.  
  2. 200 m: 118 s.  
  3. 400 m: 248 s.

• Calculation:  
  1. Vcrit ≈ 1.60 m/s (linear regression).  
  2. Pace per 100 m = 62.5 s/100 m.  
  3. Threshold adjustment: ~65 s/100 m.

• Training Zones:  
  1. Light Aerobic (Z1): 72-78 s/100 m.  
     • Set: 10x100 m at 1:15 with 20 s rest.
  2. Intense Aerobic (Z3): 65-68 s/100 m.  
     • Set: 5x200 m at 2:14 with 30 s rest.
  3. Anaerobic Threshold (Z4): 60-63 s/100 m.  
     • Set: 8x50 m at 31 s with 1:30 rest.
  4. Maximum Anaerobic (Z5): <58 s/100 m.  
     • Set: 6x25 m at 13 s with 2:00 rest.

Example 3: Distance Swimmer (800 m - 1500 m)  

• Protocol Data (4 distances):  
  1. 50 m: 26 s.  
  2. 100 m: 58 s.  
  3. 200 m: 122 s.  
  4. 400 m: 255 s.

• Calculation:  
  1. Vcrit ≈ 1.52 m/s.  
  2. Pace per 100 m = 65.8 s/100 m.  
  3. Threshold adjustment: ~68 s/100 m.

• Training Zones:  
  1. Light Aerobic (Z1): 76-82 s/100 m.  
     • Set: 20x100 m at 1:20 with 10 s rest.
  2. Moderate Aerobic (Z2): 72-76 s/100 m.  
     • Set: 10x400 m at 4:48 with 15 s rest.
  3. Intense Aerobic (Z3): 68-71 s/100 m.  
     • Set: 8x500 m at 5:40 with 20 s rest.
  4. Anaerobic Threshold (Z4): 64-67 s/100 m.  
     • Set: 6x200 m at 2:10 with 30 s rest.

Practical Applications in Training

1. Monitoring:  
   • Repeat the protocol every 4-6 weeks to assess improvements in Vcrit (an increase indicates better aerobic capacity).  
   • Compare with competition times to adjust paces.

1. Specific Sets:  
   • Aerobic Endurance: 16x100 m at 90% of Vcrit (e.g., 1:12 with 15 s rest).  
   • Threshold: 5x400 m at 100% of Vcrit (e.g., 4:20 with 30 s rest).  
   • Anaerobic Power: 8x50 m at 120% of Vcrit (e.g., 30 s with 2:00 rest).

1. Personalization:  
   • Sprinters: Greater emphasis on Z4-Z5 with long rests.  
   • Distance Swimmers: Higher volume in Z1-Z3 with short rests.

Implementation Tips

• Conditions: Maintain consistency in pool depth, temperature, and stroke (freestyle is standard).  
• Correction: If the swimmer uses fins or paddles in training, adjust paces accordingly.  
• Fatigue: Avoid testing after intense sessions to prevent underestimating Vcrit.

The Relationship Between Critical Speed (Vcrit) and Lactate in High-Performance Swimmers

The relationship between critical speed (Vcrit) and lactate is a key aspect for understanding how these tests reflect physiological performance and how they can be optimized to define aerobic and anaerobic training zones. Below, I delve into this connection, explaining lactate dynamics, its interaction with Vcrit, advanced assessment methods, and specific practical applications.

Lactate Dynamics and Its Relationship with Critical Speed

Lactate is a byproduct of anaerobic glycolytic metabolism that accumulates in the blood and muscles during intense exercise. Its concentration depends on the balance between production (via anaerobic metabolism) and clearance (oxidation in mitochondria or conversion to glucose via gluconeogenesis).

• Lactate Threshold (LT): The point where lactate production begins to exceed clearance, typically between 2-4 mmol/L, depending on the individual. In swimming, it’s associated with an intensity sustainable for 30-60 minutes.  
• Maximal Lactate Steady State (MLSS): The maximum intensity where lactate concentration remains stable (typically 3-6 mmol/L in trained swimmers) during prolonged efforts (20-30 minutes). It represents the upper limit of the intense aerobic domain.  
• Vcrit and Lactate: Vcrit approximates MLSS but tends to overestimate it slightly (5-10%) due to residual anaerobic contribution, especially in tests with short distances (50-200 m).

Scientific Evidence

• Wakayoshi et al. (1992): Found that Vcrit is highly correlated with the speed at the onset of blood lactate accumulation (OBLA, 4 mmol/L) (r=0.949).  
• Toussaint and Hollander (1994): Suggest that the difference between Vcrit and MLSS is due to anaerobic capacity (y-intercept in the model), which provides additional energy in short tests.  
• Olbrecht (2000): Indicates that Vcrit can be adjusted to MLSS by adding 2-5 s/100 m to the pace, depending on training level and specialty.

Lactate Tests and Integration with Vcrit

To more precisely relate Vcrit to lactate, critical speed protocols can be combined with direct lactate measurements. Below are advanced methods:

1. Incremental Lactate Test  
   • Objective: Determine speed at lactate threshold (LT) and MLSS for comparison with Vcrit.  
   • Procedure:  
     1. Warm-Up: 800-1000 m easy.  
     2. Stages: Swim 5-7 sets of 200 m or 400 m at progressive intensities (e.g., 80%, 85%, 90%, 95%, 100%, 105% of an estimated pace).  
     3. Rest: 30-60 s between stages to take blood samples (typically from finger or earlobe).  
     4. Measurement: Analyze lactate with a portable lactate meter (e.g., Lactate Pro).
   • Results:  
     1. LT: Speed where lactate exceeds 2 mmol/L (e.g., 1.45 m/s, 69 s/100 m).  
     2. MLSS: Speed where lactate stabilizes (e.g., 1.50 m/s, 66.7 s/100 m).
   • Integration with Vcrit:  
     1. Compare with a 2-distance test (200 m and 400 m). If Vcrit = 1.54 m/s (64.9 s/100 m), it’s ~3-5% above MLSS, which is typical.
2. Direct MLSS Test  
   • Objective: Confirm the exact MLSS speed and adjust it to Vcrit.  
   • Procedure:  
     1. Swim 30 minutes at a constant speed near the estimated Vcrit (e.g., 65 s/100 m).  
     2. Measure lactate every 5-10 minutes (minimum 3 samples).  
     3. If lactate increases <1 mmol/L between minutes 10 and 30, that speed is the MLSS.
   • Example:  
     1. Speed: 1.52 m/s (65.8 s/100 m).  
     2. Initial lactate (min 10): 4.2 mmol/L.  
     3. Final lactate (min 30): 4.5 mmol/L.  
     4. Conclusion: 65.8 s/100 m is the real MLSS.
3. Combined Vcrit + Lactate Test  
   • Objective: Validate Vcrit with real-time lactate data.  
   • Procedure:  
     1. Perform a 3-distance test (50 m, 200 m, 400 m).  
     2. Measure lactate immediately after each test.
   • Example:  
     1. 50 m: 24 s, lactate = 10 mmol/L (anaerobic domain).  
     2. 200 m: 120 s, lactate = 6 mmol/L (anaerobic transition).  
     3. 400 m: 250 s, lactate = 4.8 mmol/L (near MLSS).  
     4. Calculated Vcrit: 1.55 m/s (64.5 s/100 m).  
     5. Adjustment: MLSS estimated at ~67 s/100 m (lactate ~4-5 mmol/L).

Physiological Interpretation

• Aerobic Zones:  
  • Z1 (Light Aerobic): Lactate <2 mmol/L. Predominantly fat metabolism and aerobic oxidation.  
  • Z2 (Moderate Aerobic): Lactate 2-3 mmol/L. Increased glycolytic contribution, still sustainable.  
  • Z3 (Intense Aerobic): Lactate 3-5 mmol/L (MLSS). Maximum aerobic capacity without significant accumulation.
• Anaerobic Zones:  
  • Z4 (Anaerobic Threshold): Lactate 5-8 mmol/L. Lactate tolerance, transition to anaerobic domain.  
  • Z5 (Maximum Anaerobic): Lactate >8 mmol/L. Maximum anaerobic production, rapid exhaustion.

Correlation with Vcrit

• If Vcrit = 1.54 m/s (64.9 s/100 m):  
  • Z1: ~75-80 s/100 m (lactate ~1.5-2 mmol/L).  
  • Z3: ~65-68 s/100 m (lactate ~4-5 mmol/L, MLSS).  
  • Z5: <60 s/100 m (lactate >10 mmol/L).

Advanced Practical Example

Swimmer: 400 m freestyle specialist.  

• Vcrit Test (2 distances):  
  1. 200 m: 120 s.  
  2. 400 m: 250 s.  
  3. Vcrit = 1.54 m/s (64.9 s/100 m).

• Incremental Lactate Test:  
  1. 200 m at 80 s/100 m: 1.8 mmol/L.  
  2. 200 m at 74 s/100 m: 2.5 mmol/L.  
  3. 200 m at 68 s/100 m: 4.2 mmol/L.  
  4. 200 m at 66 s/100 m: 4.5 mmol/L (MLSS).  
  5. 200 m at 62 s/100 m: 7.8 mmol/L.

• Adjustment:  
  1. Real MLSS = 66 s/100 m (1.52 m/s), ~2 s/100 m slower than Vcrit.
     Adjusted Zones:
  2. Z1: 76-80 s/100 m (lactate <2 mmol/L).  
     • Set: 15x100 m at 1:18 with 15 s rest.
  3. Z3: 66-68 s/100 m (lactate 4-5 mmol/L).  
     • Set: 6x400 m at 4:24 with 20 s rest.
  4. Z5: <62 s/100 m (lactate >8 mmol/L).  
     • Set: 8x50 m at 30 s with 2:00 rest.

Practical Applications with Lactate

1. Vcrit Validation:  
   • Use MLSS as a reference to adjust Vcrit (add 2-5 s/100 m if needed).  
   • Example: If Vcrit = 64 s/100 m but MLSS = 67 s/100 m, train Z3 at 67-70 s/100 m.

1. Specific Training:  
   • Improve MLSS: Long sets at 95-100% of MLSS (e.g., 10x200 m at 2:14 with 15 s rest).  
   • Lactate Tolerance: Short sets at 110-120% of Vcrit (e.g., 12x50 m at 30 s with 1:30 rest).

1. Monitoring:  
   • Measure post-training lactate to verify the worked zone (e.g., 4-5 mmol/L after Z3 confirms threshold).

Limitations and Considerations

• Individual Variability: Swimmers with greater anaerobic capacity (sprinters) show a Vcrit further from MLSS.  
• Fatigue: Accumulated lactate from prior tests can underestimate MLSS.  
• Equipment: Lactate meters are accurate but require calibration and practice.

Conclusion

Integrating lactate measurements with Vcrit allows for a more precise assessment of aerobic and anaerobic capacities. While Vcrit provides a practical, non-invasive starting point, lactate offers specific physiological data to refine zones and optimize performance. For a high-level swimmer, combining both approaches (Vcrit test + lactate test) is ideal for personalizing training and monitoring progress.