As the name suggests, there are 250 potential stocks to buy in the UK’s FTSE 250. And because global investors continue to shun the mid-cap index, there are plenty of quality shares trading at reasonable valuations.

Here are a pair of mid-cap stocks that I think are worth considering in September.

Fuelling athletes and, erm, me

Starting with perhaps my favourite FTSE 250 growth company right now, we have Applied Nutrition (LSE:APN). This is a leading sports nutrition company that continues to grow quickly as people prioritise the gym and healthier lifestyles.

For the 12 months to 31 July, revenue’s expected to have grown at least 50% to £160m. Management sees this figure growing to around £205m this fiscal year as Applied Nutrition launches further products and expands overseas.

The firm’s edge lies in its innovative formulas, flavours and high product quality. It’s trusted by athletes as well as casual gym goers, and it works with professional football teams such as Bolton Wanderers, Preston North End, and Wigan Athletic.

Brand ambassadors include Coleen Rooney, whose co-developed wellness range is in Holland & Barrett, and UFC fighter Paddy ‘The Baddy’ Pimblett. I’m no athlete, but I got my latest batch of supplements from the firm this week.

The biggest risk I see is a further spike in inflation. Because Applied Nutrition’s products are premium, some cash-strapped gym bunnies may start trading down to cheaper gear.

Despite this risk, and the fact the stock’s already doubled in 12 months, I’m bullish moving forward. The profitable firm is very ambitious and sees its biggest opportunity across the pond, particularly in the much larger wellness market.

The icing on the cake? Growth at a reasonable price, with the stock trading at around 21 times next year’s forecast earnings.

Hunting for exceptional growth

The second FTSE 250 stock I want to flag is Schiehallion Fund (LSE:MNTN), an investment trust focused on private companies that have transformative growth potential.

When imagining such firms, what names spring to mind? SpaceX perhaps? Or AI lab Anthropic, the fastest growing company ever? Well, Schiehallion saw the potential in both, with SpaceX held since 2019.

Another top find was Italian tech start-up Bending Spoons, which now has a $26bn market-cap on the Nasdaq. By my calculation, this represents an increase of at least 12 times the trust’s original investment.

But that’s not all. Elsewhere in the portfolio, there are exceptional growth firms I’m also excited about. These include Revolut, which now serves more customers than HSBC, and Anduril, a leading supplier of autonomous defence technology.

Meanwhile, ByteDance, the owner of TikTok, has developed the leading AI chatbot in China (Doubao). The list goes on… Databricks, Stripe, Vinted, quantum computing start-up PsiQuantum, and UK self-driving software firm Wayve.

I expect most of these companies to go public at higher valuations over the next couple of years, potentially driving attractive returns for Schiehallion shareholders.

In the meantime though, the stock could bomb if the US tech sector sells off. Also, there’s no guarantee that its top holdings (SpaceX, Bending Spoons, Anthropic, etc) will continue to drive returns as public companies.

But on balance, I think the stock’s worth considering. Especially with Anthropic gearing up for a potentially record-breaking IPO later this year.

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Ben McPoland owns shares in Applied Nutrition, HSBC, and SpaceX.