Walk into any sportswear store or browse an online retailer, and you'll immediately encounter sports bras labelled as "low impact," "medium impact," or "high impact." These classifications are fundamental to finding the right support for your needs, yet many women don't fully understand what they mean or how to determine which level they need. This guide breaks down the science behind impact levels and helps you make informed decisions about your sports bra choices.
What "Impact" Actually Means
The term "impact" refers to how much vertical and multi-directional movement your breasts experience during a particular activity. During exercise, breasts don't just bounce up and down—they move in a complex three-dimensional figure-eight pattern that varies depending on the type of movement you're doing.
Research from the Research Group in Breast Health at the University of Portsmouth has mapped this movement extensively. Their findings show that without any support, breasts can move up to 15 centimetres in any direction during high-impact activities like running. Even during walking, movement of 3-4 centimetres is common. This movement creates strain on the Cooper's ligaments—the internal connective tissue that gives breasts their shape and position.
Impact level isn't just about your activity—it's also about your cup size. Larger breasts experience more movement and momentum during any given activity, which is why cup size must factor into your support level decision.
Low Impact Support
What It Provides
Low-impact sports bras offer light compression and gentle support. They prioritise comfort, breathability, and freedom of movement over maximum control. These bras typically feature stretchy, lightweight fabrics, simple pullover designs without hooks or adjustable straps, and minimal structure.
Activities Suited for Low Impact
- Yoga (especially slower-paced styles like Yin or Restorative)
- Pilates
- Walking at a moderate pace
- Stretching and flexibility work
- Light strength training with minimal dynamic movement
- Barre classes (though some prefer medium support)
- Casual everyday wear for active lifestyles
Who Should Choose Low Impact
Low-impact bras work best for women with smaller cup sizes (typically A-B cups) doing activities with minimal bouncing. They're also excellent as comfortable everyday options for active women who want more support than a regular bra but don't need full athletic compression. If you have a larger cup size, low-impact bras may not provide adequate support even for these gentler activities—you may need to move up to medium impact.
Medium Impact Support
What It Provides
Medium-impact sports bras bridge the gap between comfort and control. They typically feature more substantial fabric, wider straps and bands, and often include light padding or lining. Some may have adjustable straps or back closures for a more customised fit. The construction provides more bounce control than low-impact options while maintaining reasonable breathability and flexibility.
Activities Suited for Medium Impact
- Cycling (road or spin classes)
- Hiking
- Power walking or speed walking
- Weight training with compound movements
- Dance classes (depending on intensity)
- Skiing and snowboarding
- Rowing
- Golf
- Vinyasa or power yoga
Who Should Choose Medium Impact
Medium-impact support works well for women with A-C cups during moderate activities, or for women with smaller cups doing more vigorous exercise. It's a versatile choice for gym sessions that combine different types of exercise. However, if you have a D cup or larger, you may find that medium impact isn't sufficient for activities on this list—particularly cycling or power walking.
When you're between support levels, always choose the higher option. You can comfortably wear high-impact support for yoga, but you can't safely wear low-impact support for running.
High Impact Support
What It Provides
High-impact sports bras are engineered for maximum support and bounce control. They use firmer, more structured fabrics and often incorporate multiple support mechanisms. Many high-impact bras combine compression (pressing breasts against the chest) with encapsulation (individually supporting each breast in a moulded cup). Features commonly include underwire, moulded cups, adjustable straps, and hook-and-eye back closures.
Activities That Require High Impact
- Running and jogging
- HIIT (High-Intensity Interval Training)
- CrossFit
- Aerobics and step classes
- Tennis, squash, and racquet sports
- Basketball, netball, and court sports
- Jumping rope or skipping
- Kickboxing and martial arts
- Horseback riding
- Any activity involving jumping, sprinting, or rapid direction changes
Who Should Choose High Impact
Anyone doing high-impact activities should be wearing high-impact support, regardless of cup size. Additionally, women with larger cup sizes (D cup and above) often benefit from high-impact bras even for activities that might be classified as medium impact. The extra breast tissue means more momentum during movement, requiring more robust support to adequately protect the Cooper's ligaments.
If you have a larger cup size and frequently do high-impact activities, look for sports bras specifically designed for your size range. Brands that specialise in D+ cups often provide better support than extended size ranges from brands primarily focused on smaller cups.
The Cup Size Factor
Your cup size significantly affects how much support you need. Here's a general guideline, though individual needs may vary:
A-B Cups
Women with smaller cup sizes have more flexibility in their support choices. A low-impact bra may suffice for moderate activities, and medium-impact bras often provide adequate support even for running. However, proper fit is still essential—a loose-fitting low-impact bra won't protect you regardless of cup size.
C-D Cups
The "middle ground" cup sizes often require moving up a support level from what the activity alone might suggest. If an activity is typically medium impact, consider high impact. For activities listed as low impact, medium support is often more appropriate.
DD/E+ Cups
Women with larger cup sizes generally need high-impact support for any activity beyond gentle yoga or walking. The additional breast tissue creates significantly more momentum and force during movement, placing greater strain on the Cooper's ligaments. Encapsulated bras (with separate cups) typically provide better support than compression-only styles for larger busts.
Signs You're Wearing the Wrong Support Level
Your body will tell you if your sports bra isn't providing enough support. Watch for these warning signs:
- Bouncing during exercise: The most obvious sign. If you can see or feel significant breast movement, you need more support.
- Breast pain or soreness: Pain during or after exercise indicates inadequate support and potential tissue strain.
- Chafing under or around the bust: Excessive movement causes friction against skin and fabric.
- Adjusting your bra constantly: If you're pulling at straps or tugging down the band during exercise, the fit or support level isn't right.
- Red marks or indentations: While some marking is normal, deep grooves or lasting redness suggest the straps are compensating for inadequate band support.
Building Your Sports Bra Collection
Most active women benefit from owning sports bras at multiple support levels. Consider building a collection that includes:
- At least one high-impact bra for your most demanding activities
- One or two medium-impact bras for versatile gym use
- A comfortable low-impact option for yoga, stretching, or rest days
Having options appropriate for different activities means you're never over-compressed when doing gentle movement, yet always adequately supported when pushing hard. Think of it like shoes—you wouldn't wear running shoes for yoga or sandals for a hike. Your sports bra deserves the same activity-specific consideration.
Understanding support levels is just part of the equation. Learn how to measure yourself correctly and discover which specific bra features matter for different workouts.