Copenhagen Adductor Exercise: Groin Injury Prevention

A landmark 2019 randomized controlled trial by Harøy et al. found that male soccer players who performed the Copenhagen adductor exercise throughout a season experienced a 41% reduction in groin injury incidence compared to controls. Despite this striking evidence, surveys consistently show fewer than 30% of team-sport programs include systematic adductor loading — leaving one of the most preventable injury categories essentially unaddressed. This guide explains how to implement, progress, and monitor the Copenhagen adductor exercise correctly so that the injury-prevention benefit translates into real competitive availability.

Why Adductor Strength Matters

Groin and hip adductor strains account for 8-18% of all injuries in soccer, ice hockey, and Australian Rules football — sports characterized by explosive direction changes and scissor-kick loading patterns. The primary injury mechanism is an eccentric overload of the adductor longus during the late swing phase of sprinting, when the hip is abducted past 25° and the adductors must decelerate the limb.

Jacobsen et al. (2020) demonstrated that a hip adduction-to-abduction strength ratio below 0.80 (measured isometrically on a dynamometer) multiplies groin injury risk by a factor of 3.5. The Copenhagen adductor exercise is one of the few exercises capable of eliciting high adductor longus EMG amplitudes (70-80% of MVIC) through a functional range without specialist equipment.

Biomechanics and Muscle Activation

In the Copenhagen adductor exercise, the top leg is supported on a bench at knee or ankle level while the athlete raises and lowers the bottom leg or holds an isometric position. The adductor longus acts eccentrically as the bottom leg descends toward the floor, exactly replicating the injury-relevant loading pattern.

EMG Activation Hierarchy

Ishøi et al. (2016) measured muscle activation across common adductor exercises using fine-wire and surface EMG:

Bench placement at the knee creates the longest external moment arm, maximizing eccentric demand on the adductor longus. Athletes with existing adductor sensitivity should start with the ankle-level variation before progressing to knee-level support.

Three-Stage Progression Protocol

The Copenhagen exercise generates high eccentric stress even with bodyweight. A staged progression is essential to avoid the DOMS-driven dropout seen in unstructured implementations.

Stage 1 — Isometric Introduction (Weeks 1-2)

Anchor the top leg at ankle level. Hold a 3-second isometric contraction with the bottom leg raised, lower for 3 seconds, rest 2 seconds between reps. Begin with 3 sets × 6 reps. Eccentric-only DOMS peaks at 48 hours; inform athletes and schedule Stage 1 at least 72 hours before match day.

Stage 2 — Dynamic Short-Lever (Weeks 3-5)

Advance to a full range-of-motion repetition with the bench at ankle level: 3-second eccentric descent, brief pause, 2-second concentric. Volume: 3-4 sets × 8-10 reps. Target a load-adjusted RPE of 7/10 on the last set.

Stage 3 — Long-Lever and Loaded Variations (Week 6+)

Move the bench contact point to the knee, extending the moment arm by approximately 40%. Once 4×12 is achievable, introduce ankle weights (2-5 kg) or use a cable pulley for external loading. Maintain the 3-second eccentric tempo throughout — time under tension, not speed, drives tendon adaptation.

In-Season and Off-Season Programming

The evidence from Harøy et al. (2019) was generated with a twice-weekly in-season protocol. The following structure replicates those conditions while integrating with common team-sport weekly structures.

Off-Season Block (12 Weeks)

Sessions: 3 per week, non-consecutive days. Weeks 1-3: Stage 1 protocol. Weeks 4-7: Stage 2 protocol, add 1 set per week up to 5 sets. Weeks 8-11: Stage 3 protocol with progressive loading. Week 12: deload — reduce volume by 50%, maintain eccentric tempo. Pair with Copenhagen in a hip-health superset: adductor exercise then hip abductor band walk (2×15 each direction) for balanced hip musculature.

In-Season Maintenance (Playing Season)

Reduce to 2 sessions per week, scheduled on training days at least 48 hours before match. Hold 3-4 sets × 8 reps at Stage 2-3 level. Do not drop below 2 weekly sessions — Harøy et al. found the protective effect attenuates when frequency falls to once weekly.

Load Monitoring with Jump Symmetry

The Copenhagen exercise is inherently unilateral and eccentric-dominant, making it one of the harder exercises to auto-regulate by feel. Two objective indicators help confirm appropriate loading:

Single-Leg CMJ Symmetry Index

Perform 3 single-leg countermovement jumps per side before each session. Calculate the Limb Symmetry Index (LSI = weaker side / stronger side × 100). An LSI below 90% on the adductor side suggests residual fatigue or inhibition — reduce that day's volume by 30% and monitor over 72 hours. LSI above 95% green-lights full prescribed load.

Soreness-Adjusted Volume

Rate adductor soreness on a 0-10 scale before each session. Score 0-2: proceed as planned. Score 3-5: reduce sets by one, maintain reps. Score 6+: substitute with isometric holds only. This graded approach maintains training frequency — the single most important variable for injury prevention — without accumulating harmful eccentric stress.

Common Errors and Cues

• Error — Pelvis drop: Athletes allow the pelvis to sag toward the floor during the eccentric phase, shifting load to the hip flexors. Cue: "Keep your hip bone in line with your shoulder from the side view."
• Error — Rushing the eccentric: The protective effect of the exercise lives in the slow eccentric phase. Counting aloud "one-two-three" during the descent ensures compliance.
• Error — Gripping with the top knee: Athletes squeeze the bench with the top knee, creating knee valgus stress. The top leg should simply rest, not grip. Place a foam pad between bench and knee as a tactile cue.
• Error — Starting at Stage 3: Athletes and coaches unfamiliar with the exercise's eccentric intensity frequently start at the long-lever variation, producing severe 5-7-day DOMS that disrupts subsequent training. Always start at Stage 1 regardless of fitness level.
• Programming tip: Place Copenhagen at the end of the main training block but before conditioning work. Post-fatigue execution does not reduce EMG amplitude for this exercise (Ishøi et al., 2016) but placing it after conditioning increases DOMS risk without benefit.