If you look at the returns your stocks and exchange-traded funds (ETFs) have produced over the past year or so, you may be inclined to think your retirement savings portfolio is in trouble. But it is important not to dwell on the current volatility or even check your balances very often because the fluctuations are short-term, and they will pass.

That said, these types of markets are not a bad time to revisit your retirement investment strategy to make sure it is still on track to meet your goals. With growth stocks and ETFs down so sharply, it might be worth considering picking up some growth-oriented investments at lower valuations to supercharge your portfolio when the market turns. Here are two growth ETFs with lower valuations, slightly less risk, and robust growth potential.

1. Invesco S&P MidCap Momentum ETF

The Invesco S&P MidCap Momentum ETF (XMMO -0.29%) is an overlooked gem among ETFs. It tracks the S&P Midcap 400 Momentum Index, which is made up of approximately 80 mid-cap stocks that have the highest momentum scores or upward price movements as compared to other stocks within the larger S&P Midcap 400 Index. It is rebalanced twice a year, in March and September. They are weighted by their momentum score and market cap.

So, this seeks to ensure that the fastest-growing mid-caps are included in the portfolio at any given period. At present, as would be expected, energy makes up the bulk of the portfolio -- about 23% -- given that energy stocks have outperformed all others. Industrials at 21% and financials at 12% are the next two largest sectors represented in the fund. The three largest positions are EQT, Targa Resources, and Carlisle Companies. The first two are energy companies, and the last makes various building products and equipment for industrial use.

The performance has been excellent over time. The fund is down 10.5% over the past 12 months as of Aug. 31. However, its long-term five- and 10-year annualized returns are strong at 16.1% and 14.2%, respectively. These returns far outperform the S&P MidCap 400, which has five- and 10-year annualized returns of 8.7% and 11.3%, respectively.

The ETF is also very cheap right now, with a price-to-earnings ratio of 14.7, which is far below the category average for mid-cap growth funds – which is roughly 38. With a below-average valuation, it may be less risky than a similar ETF with a higher price-to-earnings (P/E) ratio, particularly in this uncertain market.

2. Invesco S&P 500 Equal Weight Technology ETF

Staying within the Invesco fund family, there is another fund, the Invesco S&P 500 Equal Weight Technology ETF (RSPT 0.15%), that doesn't get the attention that other technology ETFs get. But this ETF has outstanding performance and is built to be less volatile than many of its competitors.

This ETF tracks the S&P 500 Equal Weight Information Technology Index, which includes stocks within the S&P 500 that are considered technology stocks. Yet, unlike most, the stocks are equally weighted, which reduces volatility, yet still produces the type of alpha to beat the S&P 500 over the long term.

The ETF currently holds 77 stocks, with the largest segment, 26%, coming from the semiconductor industry. Information technology services is next with 25%, while software represents 24% of the portfolio. No one position is larger than 1.47% -- so Apple and Microsoft have roughly the same weight as Citrix Systems or Visa.

The ETF's performance has been stellar, as it has beaten the S&P 500 over time. Over the past year, it is down roughly 16.5% as of Aug. 31. But it has an annualized return of 15.2% over the past five years and 17.8% over the past 10 years, through Aug. 31. In comparison, the S&P 500 has a five-year annualized return of 11.8% and a 10-year year average return of 13.1% over the same period.

This ETF also has a P/E ratio of 23, which is lower than the average technology fund, which is about 27. But the fact that it is equal-weighted provides a little more stability, with a lower standard deviation, than some of its peers.

These two ETFs may be good options for investors who are looking for long-term growth with slightly less risk than others in their class.