Your Weaker Side — Week 20

Hey {{first name | reader}},

It’s Tuesday, which means your weekly fitness check-in. Welcome to Week #20. I've been doing single-leg curls for about two weeks now and the discovery was humbling. My left hamstring is noticeably weaker than my right — not a little weaker, meaningfully weaker. I've been training seriously for decades and somehow missed this entirely. The bilateral leg curl machine had been covering for my left leg the whole time, letting my right side quietly do the majority of the work while my left coasted. This is, apparently, extremely common. It is also, apparently, something I should have been checking.

We all have a dominant side the way we have a dominant hand, and minor strength differences between left and right are normal and expected. Studies show the dominant hand can be approximately 10% stronger than the non-dominant hand — and interestingly, left-handed people tend to show less difference between sides, likely because they've spent their lives adapting to a right-handed world and end up using both hands more.

The problem isn't the minor difference. The problem is when the difference becomes significant — and when bilateral exercises (the kind where both sides work together) quietly allow the stronger side to compensate without you ever noticing. During bilateral movements, your dominant side may be doing 55% of the work while your weaker side coasts at 45% — which is why people can train for years without fixing imbalances they don't even know they have.

Beyond aesthetics, significant imbalances carry real risk. Muscle imbalances place greater stress on joints and force other muscle groups to do more work than they normally would — and can decrease performance because the body isn't working efficiently. In my case, a weaker left hamstring means my right leg has been absorbing more load on deadlifts, squats, and every hill on the Saturday hike. That's also a plausible contributing factor to the kinds of injuries I've written about in this newsletter — my chronic achilles issues, for instance, are on the left.¹

The fix is straightforward even if it takes time: unilateral work. Exercises that work one side at a time — single-leg deadlifts, Bulgarian split squats, single-arm rows — strengthen weaker areas without allowing the dominant side to compensate. Start with the weaker side first and match reps on the stronger side. Do not let the stronger side do extra reps to "make up" for the difference — that just widens the gap. Most mild to moderate imbalances improve within 6–12 weeks of consistent targeted training.

The grip strength differential I mentioned — my left hand significantly weaker than my right — affects both my deadlifts and my pullups in ways I've been working around rather than addressing. That stops now too.²

Question: How do I know if my muscle imbalance is bad enough to worry about?

Answer: A small difference — 10% or less between sides — is normal and not worth losing sleep over. The threshold to pay attention is when the imbalance affects your movement: if your barbell tilts during a squat, if you feel one side working noticeably harder than the other, or if you keep getting injured on the same side. That last one is the tell. Recurring injuries on one side are often the body's way of reporting an imbalance you haven't addressed. The good news is that unilateral work — single-leg and single-arm exercises — both reveals and fixes the problem at the same time. Start there.³

Myth: Bilateral exercises will build equal strength on both sides.

Reality: Not if one side is already stronger. Barbell work and bilateral machines allow the dominant side to quietly take over — you may feel like you're working both sides equally when you're not. The bar stays level, the machine moves smoothly, and your weaker side is coasting. The only way to know what each side is actually doing is to isolate it. Unilateral exercises are diagnostic as much as they are corrective — the single-leg curl that revealed my hamstring imbalance taught me more in one set than months of bilateral leg curls.

Recovery weeks call for anti-inflammatory eating, which mostly means not overthinking it. Current staple: smoked salmon on rye crispbread with thinly sliced red onion, a few capers, and a squeeze of lemon. Firm textures, no cooking, takes three minutes. High protein, omega-3s, and the kind of meal that makes you feel like you have your life together even when your left hamstring has been quietly freeloading for years.⁴^^[4]

The GoodRx breakdown of muscle imbalances is practical and well-sourced — it covers causes, the research on dominant-side strength differentials, and correction strategies without veering into physical therapy jargon. Worth a read before your next unilateral session.

Run a Bilateral Audit Pick three exercises you do regularly with both sides at once — leg curl, bicep curl, shoulder press, whatever's in your rotation. Do them one side at a time this week. Note whether one side feels harder, shakier, or gives out sooner. That's your imbalance map. Then for any exercise where you find a gap: start with the weaker side, match reps on the stronger side, and don't add weight to the stronger side until both sides can handle it.

Stay strong,
{{first name | reader}}

P.S. My left hamstring and I are having a serious conversation. It has been getting a free ride for years. That ends now.